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 {@Rulepublic final StandardOutputStreamLog log = new StandardOutputStreamLog();@Autowiredprivate MediaPlayer player;@Autowiredprivate CompactDisc cd;@Testpublic void cdShouldNotBeNull() {assertNotNull(cd);}@Testpublic 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 moreError 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 moresoundsystem.CDPlayerTest > play FAILEDorg.springframework.beans.factory.BeanCreationExceptionCaused by: org.springframework.beans.factory.BeanCreationExceptionCaused 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。
@Beanpublic 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
@Beanpublic 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 {@Rulepublic final StandardOutputStreamLog log = new StandardOutputStreamLog();@Autowiredprivate MediaPlayer player;@Testpublic 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。
![org.jeecgframework.core.common.exception.MyExceptionHandler]java.lang.NullPointerException](https://images2015.cnblogs.com/blog/983815/201701/983815-20170119133730375-1432153666.png)
