Spring实战——通过Java代码装配bean
上篇说的是无需半行xml配置完成bean的自动化注入。这篇仍然不要任何xml配置,通过Java代码也能达到同样的效果。
这么说,是要把上篇的料拿出来再煮一遍? 当然不是,上篇我们几乎都在用注解的方式如@ComponentScan @Component等就完成了自动化注入,但是这些注解不是无所不能的,有些地方它也是望尘莫及的,比如第三方类库,你总不能跑到人家jar包或者库里面悄悄的加上这些注解再伪装成原来的样子用吧,太丑了! 所以,Spring可以通过显示配置的方式来解决,第一种前面有介绍过,就是通过xml来显示声明bean,第二种就是这里要介绍的基于Java代码方式装配bean。
基于注解的自动化注入固然优雅,但是它也有鞭长莫及的时候,这时候就来看看Java代码如何装配bean的。
还记的上篇的配置类CDPlayerConfig是长这样的
@Configuration @ComponentScan public class CDPlayerConfig { }
有了这个万能的组件扫描注解,一切都是那么只能,只需要在bean类上加上如@Component注解,Spring就会自动为该类创建相应的bean类。
但是现在因为我们有一些第三方类库,我们没办法去深入类中加上这些标记了,所以@ComponentScan就失去了威力和意义。
这篇的CDPlayerConfig应该长这样
@Configuration public class CDPlayerConfig { }
@Configuration注解表示该类是一个配置类。显然要创建的bean的信息是要放到这个类中的。
基于其他类以及类中的方法不变比如CompactDisc, CDPlayer, SgtPeppers等。编写测试方法如下
@RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration(classes=CDPlayerConfig.class) public class CDPlayerTest { @Rule public final StandardOutputStreamLog log = new StandardOutputStreamLog(); @Autowired private MediaPlayer player; @Autowired private CompactDisc cd; @Test public void cdShouldNotBeNull() { assertNotNull(cd); } @Test public void play() { player.play(); assertEquals( "Playing Sgt. Pepper's Lonely Hearts Club Band by The Beatles\r\n", log.getLog()); } }
首先从代码来看就会出现如下的注入错误
这里显示MediaPlayer无法注入。同时运行程序得到结果如下
Testing started at 0:20 ... 0:20:03: Executing external tasks 'cleanTest test'... :cleanTest :compileJava :processResources UP-TO-DATE :classes :compileTestJava :processTestResources UP-TO-DATE :testClasses :test 一月 15, 2017 12:20:06 上午 org.springframework.test.context.TestContextManager retrieveTestExecutionListeners 信息: Could not instantiate TestExecutionListener [org.springframework.test.context.web.ServletTestExecutionListener]. Specify custom listener classes or make the default listener classes (and their required dependencies) available. Offending class: [javax/servlet/ServletContext] 一月 15, 2017 12:20:06 上午 org.springframework.test.context.TestContextManager retrieveTestExecutionListeners 信息: Could not instantiate TestExecutionListener [org.springframework.test.context.transaction.TransactionalTestExecutionListener]. Specify custom listener classes or make the default listener classes (and their required dependencies) available. Offending class: [org/springframework/transaction/interceptor/TransactionAttributeSource] 一月 15, 2017 12:20:06 上午 org.springframework.context.support.GenericApplicationContext prepareRefresh 信息: Refreshing org.springframework.context.support.GenericApplicationContext@6adf0b01: startup date [Sun Jan 15 00:20:06 CST 2017]; root of context hierarchy 一月 15, 2017 12:20:06 上午 org.springframework.test.context.TestContextManager prepareTestInstance 严重: Caught exception while allowing TestExecutionListener [org.springframework.test.context.support.DependencyInjectionTestExecutionListener@61c715e8] to prepare test instance [soundsystem.CDPlayerTest@1081b08c] org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'soundsystem.CDPlayerTest': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private soundsystem.MediaPlayer soundsystem.CDPlayerTest.player; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [soundsystem.MediaPlayer] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)} at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:293) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1186) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireBeanProperties(AbstractAutowireCapableBeanFactory.java:384) at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.injectDependencies(DependencyInjectionTestExecutionListener.java:110) at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.prepareTestInstance(DependencyInjectionTestExecutionListener.java:75) at org.springframework.test.context.TestContextManager.prepareTestInstance(TestContextManager.java:331) at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.createTest(SpringJUnit4ClassRunner.java:213) at org.springframework.test.context.junit4.SpringJUnit4ClassRunner$1.runReflectiveCall(SpringJUnit4ClassRunner.java:290) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.methodBlock(SpringJUnit4ClassRunner.java:292) at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:233) at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:87) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229) at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61) at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:71) at org.junit.runners.ParentRunner.run(ParentRunner.java:309) at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:176) at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecuter.runTestClass(JUnitTestClassExecuter.java:105) at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecuter.execute(JUnitTestClassExecuter.java:56) at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassProcessor.processTestClass(JUnitTestClassProcessor.java:64) at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.processTestClass(SuiteTestClassProcessor.java:50) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:497) at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:35) at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24) at org.gradle.messaging.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:32) at org.gradle.messaging.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:93) at com.sun.proxy.$Proxy2.processTestClass(Unknown Source) at org.gradle.api.internal.tasks.testing.worker.TestWorker.processTestClass(TestWorker.java:106) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:497) at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:35) at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24) at org.gradle.messaging.remote.internal.hub.MessageHub$Handler.run(MessageHub.java:360) at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:54) at org.gradle.internal.concurrent.StoppableExecutorImpl$1.run(StoppableExecutorImpl.java:40) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:745) Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: private soundsystem.MediaPlayer soundsystem.CDPlayerTest.player; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [soundsystem.MediaPlayer] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)} at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:509) at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:87) at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:290) ... 46 more Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [soundsystem.MediaPlayer] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)} at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoSuchBeanDefinitionException(DefaultListableBeanFactory.java:1118) at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:967) at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:862) at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:481) ... 48 more Error creating bean with name 'soundsystem.CDPlayerTest': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private soundsystem.MediaPlayer soundsystem.CDPlayerTest.player; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [soundsystem.MediaPlayer] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)} org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'soundsystem.CDPlayerTest': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private soundsystem.MediaPlayer soundsystem.CDPlayerTest.player; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [soundsystem.MediaPlayer] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)} at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:293) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1186) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireBeanProperties(AbstractAutowireCapableBeanFactory.java:384) at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.injectDependencies(DependencyInjectionTestExecutionListener.java:110) at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.prepareTestInstance(DependencyInjectionTestExecutionListener.java:75) at org.springframework.test.context.TestContextManager.prepareTestInstance(TestContextManager.java:331) at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.createTest(SpringJUnit4ClassRunner.java:213) at org.springframework.test.context.junit4.SpringJUnit4ClassRunner$1.runReflectiveCall(SpringJUnit4ClassRunner.java:290) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.methodBlock(SpringJUnit4ClassRunner.java:292) at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:233) at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:87) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229) at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61) at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:71) at org.junit.runners.ParentRunner.run(ParentRunner.java:309) at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:176) at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecuter.runTestClass(JUnitTestClassExecuter.java:105) at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecuter.execute(JUnitTestClassExecuter.java:56) at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassProcessor.processTestClass(JUnitTestClassProcessor.java:64) at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.processTestClass(SuiteTestClassProcessor.java:50) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:497) at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:35) at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24) at org.gradle.messaging.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:32) at org.gradle.messaging.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:93) at com.sun.proxy.$Proxy2.processTestClass(Unknown Source) at org.gradle.api.internal.tasks.testing.worker.TestWorker.processTestClass(TestWorker.java:106) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:497) at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:35) at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24) at org.gradle.messaging.remote.internal.hub.MessageHub$Handler.run(MessageHub.java:360) at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:54) at org.gradle.internal.concurrent.StoppableExecutorImpl$1.run(StoppableExecutorImpl.java:40) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:745) Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: private soundsystem.MediaPlayer soundsystem.CDPlayerTest.player; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [soundsystem.MediaPlayer] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)} at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:509) at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:87) at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:290) ... 46 more Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [soundsystem.MediaPlayer] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)} at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoSuchBeanDefinitionException(DefaultListableBeanFactory.java:1118) at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:967) at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:862) at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:481) ... 48 more soundsystem.CDPlayerTest > play FAILED org.springframework.beans.factory.BeanCreationException Caused by: org.springframework.beans.factory.BeanCreationException Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException 1 test completed, 1 failed :test FAILED FAILURE: Build failed with an exception. * What went wrong: Execution failed for task ':test'. > There were failing tests. See the report at: file:///C:/Users/Administrator/Desktop/spring_video/SpringiA4_SourceCode/Chapter_02/stereo-javaconfig/build/reports/tests/index.html * Try: Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. BUILD FAILED Total time: 4.59 secs There were failing tests. See the report at: file:///C:/Users/Administrator/Desktop/spring_video/SpringiA4_SourceCode/Chapter_02/stereo-javaconfig/build/reports/tests/index.html
究其原因,主要是既没有在xml中没有声明相应的bean,也没有添加@ComponentScan启动自动扫描组件机制。
所以这里还是需要在CDPlayerConfig配置类中做文章。
声明bean
通过注解@Bean声明一个bean对象。
@Bean public CompactDisc compactDisc() { return new SgtPeppers(); }
该声明好比在xml中添加
<bean id="sgtPeppers" class="soundsystem.SgtPeppers"/>
通过这种方式,Spring会默认为SgtPeppers创建一个名为sgtPeppers的bean,如果你想换个名字,只需要在@Bean后面加上类似(name="lonelyHeartClubBand")这样的属性即可。
如果你的野心远不止满足于通过Java代码创建一个bean的话,其实你还试试如何在CDPlayer中播放CompactDisc,那就需要在CDPlayer中注入CompactDisc的bean了。于是我们可以这样声明
@Bean public CDPlayer cdPlayer(CompactDisc compactDisc) { return new CDPlayer(compactDisc); }
加上@Bean注解,表明cdPlayer()方法会创建一个bean实例并将其注册到Spring的应用上下文中,显然bean的名字默认就是cdPlayer。在执行这个方法的时候,Spring会拦截所有对方法的调用,当然这里会传入Spring注册好的CompactDisc的实例bean给cdPlayer方法来确保返回的是创建好的cdPlayer的bean。注意这里的bean是单例的,其实在xml中配置的bean如果没有特殊声明,默认也是单例的。也就是说即使这里创建了多个类似cdPlayer的方法,得到的仍然是同一个cdPlayer的bean。
这时候运行测试类CDPlayerTest
@RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration(classes=CDPlayerConfig.class) public class CDPlayerTest { @Rule public final StandardOutputStreamLog log = new StandardOutputStreamLog(); @Autowired private MediaPlayer player; @Test public void play() { player.play(); assertEquals( "Playing Sgt. Pepper's Lonely Hearts Club Band by The Beatles\r\n", log.getLog()); } }
测试通过。
表明CDPlayer注入成功。前面通过Java代码注册的Bean有效。
如果您觉得阅读本文对您有帮助,请点一下“推荐”按钮,您的“推荐”将是我最大的写作动力!如果您想持续关注我的文章,请扫描二维码,关注JackieZheng的微信公众号,我会将我的文章推送给您,并和您一起分享我日常阅读过的优质文章。