[Spring Framework]学习笔记--Dependency injection(DI)
1. 通过构造函数实现DI
简单类型实例
package examples; public class ExampleBean { // Number of years to calculate the Ultimate Answer private int years; // The Answer to Life, the Universe, and Everything private String ultimateAnswer;
//如果不能在debug模式下进行编译,必须要加下面一行。针对下面的方式3,通过参数名字。
@ConstructorProperties({"years", "ultimateAnswer"})
public ExampleBean(int years, String ultimateAnswer) { this.years = years; this.ultimateAnswer = ultimateAnswer; } }
相应的xml配置为
<bean id="exampleBean" class="examples.ExampleBean">
//方式1,通过类型,如果存在两个参数同类型的话,不行。 <constructor-arg type="int" value="7500000"/> <constructor-arg type="java.lang.String" value="42"/>
//方式2,通过参数位置。
<constructor-arg index="0" value="7500000"/>
<constructor-arg index="1" value="42"/>
//方式3,通过参数名字。
<constructor-arg name="years" value="7500000"/>
<constructor-arg name="ultimateAnswer" value="42"/>
</bean>
对象类型实例
package x.y; public class Foo { public Foo(Bar bar, Baz baz) { // ... } }
xml配置
<beans> <bean id="foo" class="x.y.Foo"> <constructor-arg ref="bar"/>
<constructor-arg ref="baz"/> </bean> <bean id="bar" class="x.y.Bar"/> <bean id="baz" class="x.y.Baz"/> </beans>
参数也可以像下面这样指定
<constructor-arg> <ref bean="bar"/> </constructor-arg>
如果是通过工厂模式,可以采用下面的方式
<bean id="exampleBean" class="examples.ExampleBean" factory-method="createInstance"> <constructor-arg ref="anotherExampleBean"/> <constructor-arg ref="yetAnotherBean"/> <constructor-arg value="1"/> </bean> <bean id="anotherExampleBean" class="examples.AnotherBean"/> <bean id="yetAnotherBean" class="examples.YetAnotherBean"/>
public class ExampleBean { // a private constructor private ExampleBean(...) { ... } // a static factory method; the arguments to this method can be // considered the dependencies of the bean that is returned, // regardless of how those arguments are actually used. public static ExampleBean createInstance ( AnotherBean anotherBean, YetAnotherBean yetAnotherBean, int i) { ExampleBean eb = new ExampleBean (...); // some other operations... return eb; } }
2. 通过set方法来实现DI
<bean id="exampleBean" class="examples.ExampleBean"> <!-- setter injection using the nested ref element --> <property name="beanOne"> <ref bean="anotherExampleBean"/> </property> <!-- setter injection using the neater ref attribute --> <property name="beanTwo" ref="yetAnotherBean"/> <property name="integerProperty" value="1"/> </bean> <bean id="anotherExampleBean" class="examples.AnotherBean"/> <bean id="yetAnotherBean" class="examples.YetAnotherBean"/>
注:property的name是和set方法中的名字一致的。
public class ExampleBean { private AnotherBean beanOne; private YetAnotherBean beanTwo; private int i; public void setBeanOne(AnotherBean beanOne) { this.beanOne = beanOne; } public void setBeanTwo(YetAnotherBean beanTwo) { this.beanTwo = beanTwo; } public void setIntegerProperty(int i) { this.i = i; } }
总结:在我们日常的工程中,上面两种方式如何使用呢?
可以从需要来看,如果这个属性是必须的,那就放在构造函数中;如果是可选的,那就用set的方式好了。