Google 开源的这个库，性能快到让程序员飞起来！

                <div><div><p></p><p><span><strong><span>来自|&nbsp;</span></strong><strong><span>开发者技术前线&nbsp; 编辑 |&nbsp;</span></strong></span><strong><span>可可</span></strong></p></div></div><div><div><div><div><div><div><blockquote><div><div><p><span><span>作者：</span></span><span>GinoBeFunny</span><span><span><span></span></span><span></span></span></p><p><span>来源：</span><span>https://url.cn/5cb6Lkw</span></p></div></div></blockquote></div></div></div></div></div></div><p></p><p>Google开源的一个依赖注入类库<strong><span>Guice</span></strong>，相比于Spring IoC 来说更小更快。Elasticsearch大量使用了Guice，本文简单的介绍下Guice的基本概念和使用方式。</p><h2><a name="t0"></a><a name="t0"></a>学习目标</h2><ul class="list-paddingleft-2"><li><p><span><span>概述：了解Guice是什么，有什么特点；</span></span></p></li><li><p><span><span>快速开始：通过实例了解Guice；</span></span></p></li><li><p><span><span>核心概念：了解Guice涉及的核心概念，如绑定（Binding）、范围（Scope）和注入（Injection）；</span></span></p></li><li><p><span><span>最佳实践：官方推荐的最佳实践；</span></span></p></li></ul><h2><a name="t1"></a><a name="t1"></a>Guice概述</h2><ul class="list-paddingleft-2"><li><p><span><span>Guice是Google开源的依赖注入类库，通过Guice减少了对工厂方法和new的使用，使得代码更易交付、测试和重用；</span></span></p></li><li><p><span><span>Guice可以帮助我们更好地设计API，它是个轻量级非侵入式的类库；</span></span></p></li><li><p><span><span>Guice对开发友好，当有异常发生时能提供更多有用的信息用于分析；</span></span></p></li></ul><h2><a name="t2"></a><a name="t2"></a>快速开始</h2><p>假设一个在线预订Pizza的网站，其有一个计费服务接口：</p><pre class="has" name="code"><code class="language-javascript hljs"><ol class="hljs-ln"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">public interface BillingService {  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-comment"><span class="hljs-comment"><span class="hljs-comment">/**   </span></span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="3"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"><span class="hljs-comment">  * 通过信用卡支付。无论支付成功与否都需要记录交易信息。  </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="4"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"><span class="hljs-comment">  *    </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="5"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"><span class="hljs-comment">  * @return 交易回执。支付成功时返回成功信息，否则记录失败原因。 </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="6"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"><span class="hljs-comment">  */</span></span>    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="7"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  Receipt chargeOrder(PizzaOrder order, CreditCard creditCard);  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="8"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">}</div></div></li></ol></code><div class="hljs-button signin" data-title="登录后复制" onclick="hljs.signin(event)"></div></pre><p>使用new的方式获取信用卡支付处理器和数据库交易日志记录器：</p><pre class="has" name="code"><code class="language-javascript hljs"><ol class="hljs-ln"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">public <span class="hljs-class"><span class="hljs-keyword"><span class="hljs-class"><span class="hljs-keyword">class</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">RealBillingService</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">implements</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">BillingService</span></span></span><span class="hljs-class"> </span></span>{   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  public Receipt chargeOrder(PizzaOrder order, CreditCard creditCard) {  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="3"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    CreditCardProcessor processor = <span class="hljs-keyword"><span class="hljs-keyword">new</span></span> PaypalCreditCardProcessor();   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="4"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    TransactionLog transactionLog = <span class="hljs-keyword"><span class="hljs-keyword">new</span></span> DatabaseTransactionLog();  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="5"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    <span class="hljs-keyword"><span class="hljs-keyword">try</span></span> {  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="6"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">      ChargeResult result = processor.charge(creditCard, order.getAmount()); </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="7"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">      transactionLog.logChargeResult(result);    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="8"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">      <span class="hljs-keyword"><span class="hljs-keyword">return</span></span> result.wasSuccessful()    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="9"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">          ? Receipt.forSuccessfulCharge(order.getAmount())   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="10"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">          : Receipt.forDeclinedCharge(result.getDeclineMessage());  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="11"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">     } <span class="hljs-keyword"><span class="hljs-keyword">catch</span></span> (UnreachableException e) {   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="12"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">      transactionLog.logConnectException(e);    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="13"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">      <span class="hljs-keyword"><span class="hljs-keyword">return</span></span> Receipt.forSystemFailure(e.getMessage());    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="14"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    }   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="15"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  } </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="16"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">}</div></div></li></ol></code><div class="hljs-button signin" data-title="登录后复制" onclick="hljs.signin(event)"></div></pre><p>使用new的问题是使得代码耦合，不易维护和测试。比如在UT里不可能直接用真实的信用卡支付，需要Mock一个CreditCardProcessor。相比于new，更容易想到的改进是使用工厂方法，但是工厂方法在测试中仍存在问题（因为通常使用全局变量来保存实例，如果在用例中未重置可能会影响其他用例）。更好的方式是通过构造方法注入依赖：</p><pre class="has" name="code"><code class="language-javascript hljs"><ol class="hljs-ln"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">public <span class="hljs-class"><span class="hljs-keyword"><span class="hljs-class"><span class="hljs-keyword">class</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">RealBillingService</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">implements</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">BillingService</span></span></span><span class="hljs-class"> </span></span>{   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  private final CreditCardProcessor processor;   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="3"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  private final TransactionLog transactionLog;   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="4"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  public RealBillingService(CreditCardProcessor processor,   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="5"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">      TransactionLog transactionLog) {   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="6"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    <span class="hljs-keyword"><span class="hljs-keyword">this</span></span>.processor = processor;    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="7"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    <span class="hljs-keyword"><span class="hljs-keyword">this</span></span>.transactionLog = transactionLog;  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="8"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  }  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="9"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  public Receipt chargeOrder(PizzaOrder order, CreditCard creditCard) {  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="10"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    <span class="hljs-keyword"><span class="hljs-keyword">try</span></span> { </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="11"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">      ChargeResult result = processor.charge(creditCard, order.getAmount());    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="12"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">      transactionLog.logChargeResult(result);   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="13"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">      <span class="hljs-keyword"><span class="hljs-keyword">return</span></span> result.wasSuccessful()   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="14"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">          ? Receipt.forSuccessfulCharge(order.getAmount())  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="15"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">          : Receipt.forDeclinedCharge(result.getDeclineMessage());  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="16"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">     } <span class="hljs-keyword"><span class="hljs-keyword">catch</span></span> (UnreachableException e) {   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="17"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">      transactionLog.logConnectException(e);    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="18"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">      <span class="hljs-keyword"><span class="hljs-keyword">return</span></span> Receipt.forSystemFailure(e.getMessage());    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="19"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    }   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="20"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  } </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="21"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">}</div></div></li></ol></code><div class="hljs-button signin" data-title="登录后复制" onclick="hljs.signin(event)"></div></pre><p>对于真实的网站应用可以注入真正的业务处理服务类：</p><pre class="has" name="code"><code class="language-javascript hljs"><ol class="hljs-ln"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">public <span class="hljs-keyword"><span class="hljs-keyword">static</span></span> <span class="hljs-keyword"><span class="hljs-keyword">void</span></span> main(<span class="hljs-built_in"><span class="hljs-built_in">String</span></span>[] args) {  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    CreditCardProcessor processor = <span class="hljs-keyword"><span class="hljs-keyword">new</span></span> PaypalCreditCardProcessor();   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="3"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    TransactionLog transactionLog = <span class="hljs-keyword"><span class="hljs-keyword">new</span></span> DatabaseTransactionLog();  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="4"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    BillingService billingService    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="5"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">        = <span class="hljs-keyword"><span class="hljs-keyword">new</span></span> RealBillingService(processor, transactionLog);   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="6"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    ...  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="7"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  }</div></div></li></ol></code><div class="hljs-button signin" data-title="登录后复制" onclick="hljs.signin(event)"></div></pre><p>而在测试用例中可以注入Mock类：</p><pre class="has" name="code"><code class="language-javascript hljs"><ol class="hljs-ln"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">public <span class="hljs-class"><span class="hljs-keyword"><span class="hljs-class"><span class="hljs-keyword">class</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">RealBillingServiceTest</span></span></span><span class="hljs-class"> </span><span class="hljs-keyword"><span class="hljs-class"><span class="hljs-keyword">extends</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">TestCase</span></span></span><span class="hljs-class"> </span></span>{ </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  private final PizzaOrder order = <span class="hljs-keyword"><span class="hljs-keyword">new</span></span> PizzaOrder(<span class="hljs-number"><span class="hljs-number">100</span></span>);   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="3"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  private final CreditCard creditCard = <span class="hljs-keyword"><span class="hljs-keyword">new</span></span> CreditCard(<span class="hljs-string"><span class="hljs-string">"1234"</span></span>, <span class="hljs-number"><span class="hljs-number">11</span></span>, <span class="hljs-number"><span class="hljs-number">2010</span></span>);   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="4"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  private final InMemoryTransactionLog transactionLog = <span class="hljs-keyword"><span class="hljs-keyword">new</span></span> InMemoryTransactionLog();  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="5"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  private final FakeCreditCardProcessor processor = <span class="hljs-keyword"><span class="hljs-keyword">new</span></span> FakeCreditCardProcessor(); </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="6"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  public <span class="hljs-keyword"><span class="hljs-keyword">void</span></span> testSuccessfulCharge() { </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="7"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    RealBillingService billingService    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="8"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">        = <span class="hljs-keyword"><span class="hljs-keyword">new</span></span> RealBillingService(processor, transactionLog);   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="9"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    Receipt receipt = billingService.chargeOrder(order, creditCard); </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="10"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    assertTrue(receipt.hasSuccessfulCharge());  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="11"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    assertEquals(<span class="hljs-number"><span class="hljs-number">100</span></span>, receipt.getAmountOfCharge());    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="12"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    assertEquals(creditCard, processor.getCardOfOnlyCharge());  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="13"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    assertEquals(<span class="hljs-number"><span class="hljs-number">100</span></span>, processor.getAmountOfOnlyCharge());  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="14"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    assertTrue(transactionLog.wasSuccessLogged());  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="15"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  } </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="16"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">}</div></div></li></ol></code><div class="hljs-button signin" data-title="登录后复制" onclick="hljs.signin(event)"></div></pre><p>那通过Guice怎么实现依赖注入呢？首先我们需要告诉Guice如果找到接口对应的实现类，这个可以通过<strong>模块</strong>来实现：</p><pre class="has" name="code"><code class="language-javascript hljs"><ol class="hljs-ln"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">public <span class="hljs-class"><span class="hljs-keyword"><span class="hljs-class"><span class="hljs-keyword">class</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">BillingModule</span></span></span><span class="hljs-class"> </span><span class="hljs-keyword"><span class="hljs-class"><span class="hljs-keyword">extends</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">AbstractModule</span></span></span><span class="hljs-class"> </span></span>{ </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  @Override  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="3"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  protected <span class="hljs-keyword"><span class="hljs-keyword">void</span></span> configure() { </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="4"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    bind(TransactionLog.class).to(DatabaseTransactionLog.class); </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="5"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    bind(CreditCardProcessor.class).to(PaypalCreditCardProcessor.class); </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="6"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    bind(BillingService.class).to(RealBillingService.class); </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="7"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  }  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="8"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">}</div></div></li></ol></code><div class="hljs-button signin" data-title="登录后复制" onclick="hljs.signin(event)"></div></pre><p>这里的模块只需要实现Module接口或继承自AbstractModule，然后在configure方法中设置<strong>绑定</strong>（后面会继续介绍）即可。然后只需在原有的构造方法中增加@Inject注解即可<strong>注入</strong>：</p><pre class="has" name="code"><code class="language-javascript hljs"><ol class="hljs-ln"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">public <span class="hljs-class"><span class="hljs-keyword"><span class="hljs-class"><span class="hljs-keyword">class</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">RealBillingService</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">implements</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">BillingService</span></span></span><span class="hljs-class"> </span></span>{  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  private final CreditCardProcessor processor;   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="3"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  private final TransactionLog transactionLog;   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="4"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  @Inject    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="5"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  public RealBillingService(CreditCardProcessor processor,   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="6"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">      TransactionLog transactionLog) {   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="7"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    <span class="hljs-keyword"><span class="hljs-keyword">this</span></span>.processor = processor;    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="8"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    <span class="hljs-keyword"><span class="hljs-keyword">this</span></span>.transactionLog = transactionLog;  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="9"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  }  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="10"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  public Receipt chargeOrder(PizzaOrder order, CreditCard creditCard) { </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="11"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    <span class="hljs-keyword"><span class="hljs-keyword">try</span></span> { </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="12"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">      ChargeResult result = processor.charge(creditCard, order.getAmount());    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="13"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">      transactionLog.logChargeResult(result);   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="14"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">      <span class="hljs-keyword"><span class="hljs-keyword">return</span></span> result.wasSuccessful()   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="15"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">          ? Receipt.forSuccessfulCharge(order.getAmount())  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="16"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">          : Receipt.forDeclinedCharge(result.getDeclineMessage());  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="17"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">     } <span class="hljs-keyword"><span class="hljs-keyword">catch</span></span> (UnreachableException e) {   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="18"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">      transactionLog.logConnectException(e);    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="19"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">      <span class="hljs-keyword"><span class="hljs-keyword">return</span></span> Receipt.forSystemFailure(e.getMessage());    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="20"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    }   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="21"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  } </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="22"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">}</div></div></li></ol></code><div class="hljs-button signin" data-title="登录后复制" onclick="hljs.signin(event)"></div></pre><p>最后，再看看main方法中是如何调用的：</p><pre class="has" name="code"><code class="language-javascript hljs"><ol class="hljs-ln"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">public <span class="hljs-keyword"><span class="hljs-keyword">static</span></span> <span class="hljs-keyword"><span class="hljs-keyword">void</span></span> main(<span class="hljs-built_in"><span class="hljs-built_in">String</span></span>[] args) {  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    Injector injector = Guice.createInjector(<span class="hljs-keyword"><span class="hljs-keyword">new</span></span> BillingModule()); </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="3"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    BillingService billingService = injector.getInstance(BillingService.class);  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="4"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    ...  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="5"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  }</div></div></li></ol></code><div class="hljs-button signin" data-title="登录后复制" onclick="hljs.signin(event)"></div></pre><h2><a name="t3"></a><a name="t3"></a>绑定</h2><h3><a name="t4"></a><a name="t4"></a>连接绑定</h3><p>连接绑定是最常用的绑定方式，它将一个类型和它的实现进行映射。下面的例子中将TransactionLog接口映射到它的实现类DatabaseTransactionLog。</p><pre class="has" name="code"><code class="language-javascript hljs"><ol class="hljs-ln"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">public <span class="hljs-class"><span class="hljs-keyword"><span class="hljs-class"><span class="hljs-keyword">class</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">BillingModule</span></span></span><span class="hljs-class"> </span><span class="hljs-keyword"><span class="hljs-class"><span class="hljs-keyword">extends</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">AbstractModule</span></span></span><span class="hljs-class"> </span></span>{ </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  @Override  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="3"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  protected <span class="hljs-keyword"><span class="hljs-keyword">void</span></span> configure() { </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="4"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    bind(TransactionLog.class).to(DatabaseTransactionLog.class); </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="5"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  }  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="6"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">}</div></div></li></ol></code><div class="hljs-button signin" data-title="登录后复制" onclick="hljs.signin(event)"></div></pre><p>连接绑定还支持链式，比如下面的例子最终将TransactionLog接口映射到实现类MySqlDatabaseTransactionLog。</p><pre class="has" name="code"><code class="language-javascript hljs"><ol class="hljs-ln"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">public <span class="hljs-class"><span class="hljs-keyword"><span class="hljs-class"><span class="hljs-keyword">class</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">BillingModule</span></span></span><span class="hljs-class"> </span><span class="hljs-keyword"><span class="hljs-class"><span class="hljs-keyword">extends</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">AbstractModule</span></span></span><span class="hljs-class"> </span></span>{ </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  @Override  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="3"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  protected <span class="hljs-keyword"><span class="hljs-keyword">void</span></span> configure() { </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="4"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    bind(TransactionLog.class).to(DatabaseTransactionLog.class); </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="5"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    bind(DatabaseTransactionLog.class).to(MySqlDatabaseTransactionLog.class);    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="6"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  }  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="7"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">}</div></div></li></ol></code><div class="hljs-button signin" data-title="登录后复制" onclick="hljs.signin(event)"></div></pre><h3><a name="t5"></a><a name="t5"></a>注解绑定</h3><p>通过一个类型可能存在多个实现，比如在信用卡支付处理器中存在PayPal的支付和Google支付，这样通过连接绑定就搞不定。这时我们可以通过注解绑定来实现：</p><pre class="has" name="code"><code class="language-javascript hljs"><ol class="hljs-ln"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">@BindingAnnotation    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">@Target({ FIELD, PARAMETER, METHOD })    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="3"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">@Retention(RUNTIME)  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="4"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">public @interface PayPal {}  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="5"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">public <span class="hljs-class"><span class="hljs-keyword"><span class="hljs-class"><span class="hljs-keyword">class</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">RealBillingService</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">implements</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">BillingService</span></span></span><span class="hljs-class"> </span></span>{    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="6"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  @Inject    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="7"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  public RealBillingService(@PayPal CreditCardProcessor processor,   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="8"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">      TransactionLog transactionLog) {   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="9"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    ...  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="10"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  } </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="11"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">}   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="12"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"><span class="hljs-comment">// 当注入的方法参数存在@PayPal注解时注入PayPalCreditCardProcessor实现 </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="13"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">bind(CreditCardProcessor.class).annotatedWith(PayPal.class).to(PayPalCreditCardProcessor.class);</span></div></div></li></ol></code><div class="hljs-button signin" data-title="登录后复制" onclick="hljs.signin(event)"></div></pre><p>可以看到在模块的绑定时用annotatedWith方法指定具体的注解来进行绑定，这种方式有一个问题就是我们必须增加自定义的注解来绑定，基于此Guice内置了一个@Named注解满足该场景：</p><pre class="has" name="code"><code class="language-javascript hljs"><ol class="hljs-ln" style="width:993px"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">public <span class="hljs-class"><span class="hljs-keyword"><span class="hljs-class"><span class="hljs-keyword">class</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">RealBillingService</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">implements</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">BillingService</span></span></span><span class="hljs-class"> </span></span>{    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  @Inject    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="3"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  public RealBillingService(@Named(<span class="hljs-string"><span class="hljs-string">"Checkout"</span></span>) CreditCardProcessor processor,   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="4"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">      TransactionLog transactionLog) {   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="5"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    ...  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="6"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  }  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="7"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">}    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="8"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"><span class="hljs-comment">// 当注入的方法参数存在@Named注解且值为Checkout时注入CheckoutCreditCardProcessor实现  </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="9"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">bind(CreditCardProcessor.class).annotatedWith(Names.named(</span><span class="hljs-string"><span class="hljs-comment">"Checkout"</span></span><span class="hljs-comment">)).to(CheckoutCreditCardProcessor.class);</span></div></div></li></ol></code><div class="hljs-button signin" data-title="登录后复制" onclick="hljs.signin(event)"></div></pre><h3><a name="t6"></a><a name="t6"></a>实例绑定</h3><p>将一个类型绑定到一个具体的实例而非实现类，这个通过是在无依赖的对象（比如值对象）中使用。如果toInstance包含复杂的逻辑会导致启动速度，此时应该通过@Provides方法绑定。</p><pre class="has" name="code"><code class="language-javascript hljs"><ol class="hljs-ln" style="width:951px"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">bind(<span class="hljs-built_in"><span class="hljs-built_in">String</span></span>.class).annotatedWith(Names.named(<span class="hljs-string"><span class="hljs-string">"JDBC URL"</span></span>)).toInstance(<span class="hljs-string"><span class="hljs-string">"jdbc:mysql://localhost/pizza"</span></span>);  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">bind(Integer.class).annotatedWith(Names.named(<span class="hljs-string"><span class="hljs-string">"login timeout seconds"</span></span>)).toInstance(<span class="hljs-number"><span class="hljs-number">10</span></span>);</div></div></li></ol></code><div class="hljs-button signin" data-title="登录后复制" onclick="hljs.signin(event)"></div></pre><h3><a name="t7"></a><a name="t7"></a>@Provides方法绑定</h3><p>模块中定义的、带有@Provides注解的、方法返回值即为绑定映射的类型。</p><pre class="has" name="code"><code class="language-javascript hljs"><ol class="hljs-ln" style="width:951px"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">public <span class="hljs-class"><span class="hljs-keyword"><span class="hljs-class"><span class="hljs-keyword">class</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">BillingModule</span></span></span><span class="hljs-class"> </span><span class="hljs-keyword"><span class="hljs-class"><span class="hljs-keyword">extends</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">AbstractModule</span></span></span><span class="hljs-class"> </span></span>{  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  @Override  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="3"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  protected <span class="hljs-keyword"><span class="hljs-keyword">void</span></span> configure() { </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="4"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    ...  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="5"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  }  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="6"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  @Provides  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="7"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  TransactionLog provideTransactionLog() {   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="8"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    DatabaseTransactionLog transactionLog = <span class="hljs-keyword"><span class="hljs-keyword">new</span></span> DatabaseTransactionLog();  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="9"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    transactionLog.setJdbcUrl(<span class="hljs-string"><span class="hljs-string">"jdbc:mysql://localhost/pizza"</span></span>);  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="10"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    transactionLog.setThreadPoolSize(<span class="hljs-number"><span class="hljs-number">30</span></span>);  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="11"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    <span class="hljs-keyword"><span class="hljs-keyword">return</span></span> transactionLog;    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="12"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  } </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="13"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  @Provides @PayPal </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="14"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  CreditCardProcessor providePayPalCreditCardProcessor(@Named(<span class="hljs-string"><span class="hljs-string">"PayPal API key"</span></span>) <span class="hljs-built_in"><span class="hljs-built_in">String</span></span> apiKey) {    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="15"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    PayPalCreditCardProcessor processor = <span class="hljs-keyword"><span class="hljs-keyword">new</span></span> PayPalCreditCardProcessor();    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="16"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    processor.setApiKey(apiKey);    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="17"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    <span class="hljs-keyword"><span class="hljs-keyword">return</span></span> processor; </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="18"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  } </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="19"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">}</div></div></li></ol></code><div class="hljs-button signin" data-title="登录后复制" onclick="hljs.signin(event)"></div></pre><h3><a name="t8"></a><a name="t8"></a>Provider绑定</h3><p>如果使用@Provides方法绑定逻辑越来越复杂时就可以通过Provider绑定（一个实现了Provider接口的实现类）来实现。</p><pre class="has" name="code"><code class="language-javascript hljs"><ol class="hljs-ln"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">public interface Provider&lt;T&gt; {   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  T get();   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="3"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">}    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="4"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">public <span class="hljs-class"><span class="hljs-keyword"><span class="hljs-class"><span class="hljs-keyword">class</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">DatabaseTransactionLogProvider</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">implements</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">Provider</span></span></span><span class="hljs-class">&lt;</span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">TransactionLog</span></span></span><span class="hljs-class">&gt; </span></span>{    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="5"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  private final Connection connection;   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="6"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  @Inject    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="7"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  public DatabaseTransactionLogProvider(Connection connection) { </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="8"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    <span class="hljs-keyword"><span class="hljs-keyword">this</span></span>.connection = connection;  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="9"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  }  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="10"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  public TransactionLog get() { </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="11"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    DatabaseTransactionLog transactionLog = <span class="hljs-keyword"><span class="hljs-keyword">new</span></span> DatabaseTransactionLog(); </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="12"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    transactionLog.setConnection(connection);   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="13"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    <span class="hljs-keyword"><span class="hljs-keyword">return</span></span> transactionLog;    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="14"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  } </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="15"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">}   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="16"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">public <span class="hljs-class"><span class="hljs-keyword"><span class="hljs-class"><span class="hljs-keyword">class</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">BillingModule</span></span></span><span class="hljs-class"> </span><span class="hljs-keyword"><span class="hljs-class"><span class="hljs-keyword">extends</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">AbstractModule</span></span></span><span class="hljs-class"> </span></span>{ </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="17"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  @Override </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="18"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  protected <span class="hljs-keyword"><span class="hljs-keyword">void</span></span> configure() {    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="19"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    bind(TransactionLog.class).toProvider(DatabaseTransactionLogProvider.class);    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="20"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  } </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="21"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">}</div></div></li></ol></code><div class="hljs-button signin" data-title="登录后复制" onclick="hljs.signin(event)"></div></pre><h3><a name="t9"></a><a name="t9"></a>无目标绑定</h3><p>当我们想提供对一个具体的类给注入器时就可以采用无目标绑定。</p><pre class="has" name="code"><code class="language-javascript hljs"><ol class="hljs-ln"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">bind(MyConcreteClass.class);    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">bind(AnotherConcreteClass.class).in(Singleton.class);</div></div></li></ol></code><div class="hljs-button signin" data-title="登录后复制" onclick="hljs.signin(event)"></div></pre><h3><a name="t10"></a><a name="t10"></a>构造器绑定</h3><p>3.0新增的绑定，适用于第三方提供的类或者是有多个构造器参与依赖注入。通过@Provides方法可以显式调用构造器，但是这种方式有一个限制：无法给这些实例应用AOP。</p><pre class="has" name="code"><code class="language-javascript hljs"><ol class="hljs-ln" style="width:1085px"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">public <span class="hljs-class"><span class="hljs-keyword"><span class="hljs-class"><span class="hljs-keyword">class</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">BillingModule</span></span></span><span class="hljs-class"> </span><span class="hljs-keyword"><span class="hljs-class"><span class="hljs-keyword">extends</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">AbstractModule</span></span></span><span class="hljs-class"> </span></span>{ </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  @Override  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="3"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  protected <span class="hljs-keyword"><span class="hljs-keyword">void</span></span> configure() { </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="4"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    <span class="hljs-keyword"><span class="hljs-keyword">try</span></span> {  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="5"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">      bind(TransactionLog.class).toConstructor(DatabaseTransactionLog.class.getConstructor(DatabaseConnection.class));   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="6"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    } <span class="hljs-keyword"><span class="hljs-keyword">catch</span></span> (NoSuchMethodException e) {    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="7"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">      addError(e);   </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="8"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">    }    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="9"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  }  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="10"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">}</div></div></li></ol></code><div class="hljs-button signin" data-title="登录后复制" onclick="hljs.signin(event)"></div></pre><h2><a name="t11"></a><a name="t11"></a>范围</h2><p>默认情况下，Guice每次都会返回一个新的实例，这个可以通过范围（Scope）来配置。常见的范围有单例（@Singleton）、会话（@SessionScoped）和请求（@RequestScoped），另外还可以通过自定义的范围来扩展。</p><p>范围的注解可以应该在实现类、@Provides方法中，或在绑定的时候指定（优先级最高）：</p><pre class="has" name="code"><code class="language-javascript hljs"><ol class="hljs-ln"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">@Singleton  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">public <span class="hljs-class"><span class="hljs-keyword"><span class="hljs-class"><span class="hljs-keyword">class</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">InMemoryTransactionLog</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">implements</span></span></span><span class="hljs-class"> </span><span class="hljs-title"><span class="hljs-class"><span class="hljs-title">TransactionLog</span></span></span><span class="hljs-class"> </span></span>{    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="3"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">  <span class="hljs-comment"><span class="hljs-comment">/* everything here should be threadsafe! */</span></span>  </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="4"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">}    </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="5"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"><span class="hljs-comment">// scopes apply to the binding source, not the binding target </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="6"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">bind(TransactionLog.class).to(InMemoryTransactionLog.class).in(Singleton.class);  </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="7"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">@Provides @Singleton </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="8"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">TransactionLog provideTransactionLog() { </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="9"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">    ...  </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="10"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">}</span></div></div></li></ol></code><div class="hljs-button signin" data-title="登录后复制" onclick="hljs.signin(event)"></div></pre><p>另外，Guice还有一种特殊的单例模式叫饥饿单例（相对于懒加载单例来说）：</p><pre class="has" name="code"><code class="language-javascript hljs"><ol class="hljs-ln"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"><span class="hljs-comment">// Eager singletons reveal initialization problems sooner,   </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"><span class="hljs-comment">// and ensure end-users get a consistent, snappy experience.   </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="3"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">bind(TransactionLog.class).to(InMemoryTransactionLog.class).asEagerSingleton();</span></div></div></li></ol></code><div class="hljs-button signin" data-title="登录后复制" onclick="hljs.signin(event)"></div></pre><h2><a name="t12"></a><a name="t12"></a>注入</h2><p>依赖注入的要求就是将行为和依赖分离，它建议将依赖注入而非通过工厂类的方法去查找。注入的方式通常有构造器注入、方法注入、属性注入等。</p><pre class="has" name="code"><code class="language-javascript hljs"><ol class="hljs-ln"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"><span class="hljs-comment">// 构造器注入  </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">public </span><span class="hljs-class"><span class="hljs-keyword"><span class="hljs-comment">class</span></span><span class="hljs-comment"> </span><span class="hljs-title"><span class="hljs-comment">RealBillingService</span></span><span class="hljs-comment"> </span><span class="hljs-title"><span class="hljs-comment">implements</span></span><span class="hljs-comment"> </span><span class="hljs-title"><span class="hljs-comment">BillingService</span></span><span class="hljs-comment"> </span></span><span class="hljs-comment">{ </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="3"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  private final CreditCardProcessor processorProvider;   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="4"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  private final TransactionLog transactionLogProvider;   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="5"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  @Inject    </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="6"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  public RealBillingService(CreditCardProcessor processorProvider,   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="7"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">      TransactionLog transactionLogProvider) {   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="8"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">    </span><span class="hljs-keyword"><span class="hljs-comment">this</span></span><span class="hljs-comment">.processorProvider = processorProvider;    </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="9"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">    </span><span class="hljs-keyword"><span class="hljs-comment">this</span></span><span class="hljs-comment">.transactionLogProvider = transactionLogProvider;  </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="10"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  } </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="11"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">}   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="12"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"><span class="hljs-comment">// 方法注入  </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="13"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">public </span><span class="hljs-class"><span class="hljs-keyword"><span class="hljs-comment">class</span></span><span class="hljs-comment"> </span><span class="hljs-title"><span class="hljs-comment">PayPalCreditCardProcessor</span></span><span class="hljs-comment"> </span><span class="hljs-title"><span class="hljs-comment">implements</span></span><span class="hljs-comment"> </span><span class="hljs-title"><span class="hljs-comment">CreditCardProcessor</span></span><span class="hljs-comment"> </span></span><span class="hljs-comment">{    </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="14"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  private </span><span class="hljs-keyword"><span class="hljs-comment">static</span></span><span class="hljs-comment"> final </span><span class="hljs-built_in"><span class="hljs-comment">String</span></span><span class="hljs-comment"> DEFAULT_API_KEY = </span><span class="hljs-string"><span class="hljs-comment">"development-use-only"</span></span><span class="hljs-comment">;   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="15"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  private </span><span class="hljs-built_in"><span class="hljs-comment">String</span></span><span class="hljs-comment"> apiKey = DEFAULT_API_KEY;   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="16"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  @Inject   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="17"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  public </span><span class="hljs-keyword"><span class="hljs-comment">void</span></span><span class="hljs-comment"> setApiKey(@Named(</span><span class="hljs-string"><span class="hljs-comment">"PayPal API key"</span></span><span class="hljs-comment">) </span><span class="hljs-built_in"><span class="hljs-comment">String</span></span><span class="hljs-comment"> apiKey) { </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="18"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">    </span><span class="hljs-keyword"><span class="hljs-comment">this</span></span><span class="hljs-comment">.apiKey = apiKey; </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="19"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  } </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="20"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">}   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="21"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"><span class="hljs-comment">// 属性注入  </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="22"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">public </span><span class="hljs-class"><span class="hljs-keyword"><span class="hljs-comment">class</span></span><span class="hljs-comment"> </span><span class="hljs-title"><span class="hljs-comment">DatabaseTransactionLogProvider</span></span><span class="hljs-comment"> </span><span class="hljs-title"><span class="hljs-comment">implements</span></span><span class="hljs-comment"> </span><span class="hljs-title"><span class="hljs-comment">Provider</span></span><span class="hljs-comment">&lt;</span><span class="hljs-title"><span class="hljs-comment">TransactionLog</span></span><span class="hljs-comment">&gt; </span></span><span class="hljs-comment">{    </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="23"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  @Inject Connection connection;    </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="24"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  public TransactionLog get() { </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="25"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">    </span><span class="hljs-keyword"><span class="hljs-comment">return</span></span><span class="hljs-comment"> </span><span class="hljs-keyword"><span class="hljs-comment">new</span></span><span class="hljs-comment"> DatabaseTransactionLog(connection);  </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="26"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  } </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="27"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">}   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="28"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"><span class="hljs-comment">// 可选注入：当找不到映射时不报错   </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="29"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">public </span><span class="hljs-class"><span class="hljs-keyword"><span class="hljs-comment">class</span></span><span class="hljs-comment"> </span><span class="hljs-title"><span class="hljs-comment">PayPalCreditCardProcessor</span></span><span class="hljs-comment"> </span><span class="hljs-title"><span class="hljs-comment">implements</span></span><span class="hljs-comment"> </span><span class="hljs-title"><span class="hljs-comment">CreditCardProcessor</span></span><span class="hljs-comment"> </span></span><span class="hljs-comment">{    </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="30"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  private </span><span class="hljs-keyword"><span class="hljs-comment">static</span></span><span class="hljs-comment"> final </span><span class="hljs-built_in"><span class="hljs-comment">String</span></span><span class="hljs-comment"> SANDBOX_API_KEY = </span><span class="hljs-string"><span class="hljs-comment">"development-use-only"</span></span><span class="hljs-comment">;   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="31"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  private </span><span class="hljs-built_in"><span class="hljs-comment">String</span></span><span class="hljs-comment"> apiKey = SANDBOX_API_KEY;   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="32"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  @Inject(optional=</span><span class="hljs-literal"><span class="hljs-comment">true</span></span><span class="hljs-comment">)  </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="33"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  public </span><span class="hljs-keyword"><span class="hljs-comment">void</span></span><span class="hljs-comment"> setApiKey(@Named(</span><span class="hljs-string"><span class="hljs-comment">"PayPal API key"</span></span><span class="hljs-comment">) </span><span class="hljs-built_in"><span class="hljs-comment">String</span></span><span class="hljs-comment"> apiKey) { </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="34"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">    </span><span class="hljs-keyword"><span class="hljs-comment">this</span></span><span class="hljs-comment">.apiKey = apiKey; </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="35"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  } </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="36"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">}</span></div></div></li></ol></code><div class="hljs-button signin" data-title="登录后复制" onclick="hljs.signin(event)"></div></pre><h2><a name="t13"></a><a name="t13"></a>辅助注入</h2><p>辅助注入（Assisted Inject）属于Guice扩展的一部分，它通过@Assisted注解自动生成工厂来加强非注入参数的使用。</p><pre class="has" name="code"><code class="language-javascript hljs"><ol class="hljs-ln" style="width:1018px"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"><span class="hljs-comment">// RealPayment中有两个参数startDate和amount无法直接注入   </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">public </span><span class="hljs-class"><span class="hljs-keyword"><span class="hljs-comment">class</span></span><span class="hljs-comment"> </span><span class="hljs-title"><span class="hljs-comment">RealPayment</span></span><span class="hljs-comment"> </span><span class="hljs-title"><span class="hljs-comment">implements</span></span><span class="hljs-comment"> </span><span class="hljs-title"><span class="hljs-comment">Payment</span></span><span class="hljs-comment"> </span></span><span class="hljs-comment">{   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="3"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  public RealPayment(    </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="4"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">        CreditService creditService,  </span><span class="hljs-comment"><span class="hljs-comment">// from the Injector    </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="5"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">        AuthService authService,  </span><span class="hljs-comment"><span class="hljs-comment">// from the Injector </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="6"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">        </span><span class="hljs-built_in"><span class="hljs-comment">Date</span></span><span class="hljs-comment"> startDate, </span><span class="hljs-comment"><span class="hljs-comment">// from the instance's creator  </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="7"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">        Money amount); </span><span class="hljs-comment"><span class="hljs-comment">// from the instance's creator  </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="8"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  }   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="9"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  ...    </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="10"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">}   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="11"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"><span class="hljs-comment">// 一种方式是增加一个工厂来构造    </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="12"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">public interface PaymentFactory {    </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="13"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  public Payment create(</span><span class="hljs-built_in"><span class="hljs-comment">Date</span></span><span class="hljs-comment"> startDate, Money amount);   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="14"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">}   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="15"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">public </span><span class="hljs-class"><span class="hljs-keyword"><span class="hljs-comment">class</span></span><span class="hljs-comment"> </span><span class="hljs-title"><span class="hljs-comment">RealPaymentFactory</span></span><span class="hljs-comment"> </span><span class="hljs-title"><span class="hljs-comment">implements</span></span><span class="hljs-comment"> </span><span class="hljs-title"><span class="hljs-comment">PaymentFactory</span></span><span class="hljs-comment"> </span></span><span class="hljs-comment">{   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="16"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  private final Provider&lt;CreditService&gt; creditServiceProvider;    </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="17"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  private final Provider&lt;AuthService&gt; authServiceProvider;    </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="18"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  @Inject   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="19"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  public RealPaymentFactory(Provider&lt;CreditService&gt; creditServiceProvider,    </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="20"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">      Provider&lt;AuthService&gt; authServiceProvider) {    </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="21"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">    </span><span class="hljs-keyword"><span class="hljs-comment">this</span></span><span class="hljs-comment">.creditServiceProvider = creditServiceProvider;   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="22"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">    </span><span class="hljs-keyword"><span class="hljs-comment">this</span></span><span class="hljs-comment">.authServiceProvider = authServiceProvider;   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="23"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  } </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="24"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  public Payment create(</span><span class="hljs-built_in"><span class="hljs-comment">Date</span></span><span class="hljs-comment"> startDate, Money amount) {  </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="25"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">    </span><span class="hljs-keyword"><span class="hljs-comment">return</span></span><span class="hljs-comment"> </span><span class="hljs-keyword"><span class="hljs-comment">new</span></span><span class="hljs-comment"> RealPayment(creditServiceProvider.get(), </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="26"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">      authServiceProvider.get(), startDate, amount);    </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="27"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  } </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="28"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">}   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="29"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">bind(PaymentFactory.class).to(RealPaymentFactory.class);    </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="30"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"><span class="hljs-comment">// 通过@Assisted注解可以减少RealPaymentFactory   </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="31"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">public </span><span class="hljs-class"><span class="hljs-keyword"><span class="hljs-comment">class</span></span><span class="hljs-comment"> </span><span class="hljs-title"><span class="hljs-comment">RealPayment</span></span><span class="hljs-comment"> </span><span class="hljs-title"><span class="hljs-comment">implements</span></span><span class="hljs-comment"> </span><span class="hljs-title"><span class="hljs-comment">Payment</span></span><span class="hljs-comment"> </span></span><span class="hljs-comment">{  </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="32"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  @Inject   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="33"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  public RealPayment(   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="34"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">        CreditService creditService,    </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="35"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">        AuthService authService,    </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="36"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">        @Assisted </span><span class="hljs-built_in"><span class="hljs-comment">Date</span></span><span class="hljs-comment"> startDate,    </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="37"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">        @Assisted Money amount);    </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="38"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  } </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="39"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">  ...   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="40"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">}   </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="41"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"><span class="hljs-comment">// Guice 2.0 </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="42"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"><span class="hljs-comment">//bind(PaymentFactory.class).toProvider(FactoryProvider.newFactory(PaymentFactory.class, RealPayment.class)); </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="43"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"><span class="hljs-comment">// Guice 3.0  </span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="44"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">install(</span><span class="hljs-keyword"><span class="hljs-comment">new</span></span><span class="hljs-comment"> FactoryModuleBuilder().implement(Payment.class, RealPayment.class).build(PaymentFactory.class));</span></div></div></li></ol></code><div class="hljs-button signin" data-title="登录后复制" onclick="hljs.signin(event)"></div></pre><h2><a name="t14"></a><a name="t14"></a>最佳实践</h2><ul class="list-paddingleft-2"><li><p><span><span>最小化可变性：尽可能注入的是不可变对象；</span></span></p></li><li><p><span><span>只注入直接依赖：不用注入一个实例来获取真正需要的实例，增加复杂性且不易测试；</span></span></p></li><li><p><span><span>避免循环依赖</span></span></p></li><li><p><span><span>避免静态状态：静态状态和可测试性就是天敌；</span></span></p></li><li><p><span><span>采用@Nullable：Guice默认情况下禁止注入null对象；</span></span></p></li><li><p><span><span>模块的处理必须要快并且无副作用</span></span></p></li><li><p><span><span>在Providers绑定中当心IO问题：因为Provider不检查异常、不支持超时、不支持重试；</span></span></p></li><li><p><span><span>不用在模块中处理分支逻辑</span></span></p></li><li><p><span><span>尽可能不要暴露构造器</span></span></p></li></ul><div><div><div><div><div><div><div></div><div><div></div></div><div><span>END</span></div><div><div></div></div><div></div><br></div></div></div><div><div><div><div><div><div><div><div><div><div><div><div><div><div><div><div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div><div><div><div><div><div><div></div></div></div></div></div></div></div></div></div>
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