2.spring源码-BeanPostProcessor后置处理之ApplicationContextAwareProcessor，实现spring容器中某一个类的bean对象在初始化时需要得到Spring容器内容。

需求：我们的需求是，在spring初始化完毕时，使我们自定义一个类Bird类可以得到spring容器内容。

实现步骤：

1.首先我们来看一下ApplicationContextAwareProcessor这个类，它是BeanPostProcessor(后置处理器)的一个实现类。所以ApplicationContextAwareProcessor里面也必定有后置处理器接口的两个前置和后置方法。

我们来看一下ApplicationContextAwareProcessor的前置方法：由前面讲解的后置处理器(链接：https://www.cnblogs.com/WNof11020520/p/10598745.html)可知，所有bean对象初始化前都会执行BeanPostProcessor接口实现类的前置方法postProcessBeforeInitialization，所以所有bean对象初始化前都会执行ApplicationContextAwareProcessor的postProcessBeforeInitialization方法。

 @Nullable
     public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
         AccessControlContext acc = null;
         if(System.getSecurityManager() != null && (bean instanceof EnvironmentAware ||
                                                     bean instanceof EmbeddedValueResolverAware ||
                                                     bean instanceof ResourceLoaderAware ||
                                                     bean instanceof ApplicationEventPublisherAware ||
                                                     bean instanceof MessageSourceAware ||
                                                     bean instanceof ApplicationContextAware)) {
             acc = this.applicationContext.getBeanFactory().getAccessControlContext();
         }

         if(acc != null) {
             AccessController.doPrivileged(() -> {
                 this.invokeAwareInterfaces(bean);
                 return null;
             }, acc);
         } else {
             this.invokeAwareInterfaces(bean);
         }

         return bean;
     }

     private void invokeAwareInterfaces(Object bean) {
         if(bean instanceof Aware) {
             if(bean instanceof EnvironmentAware) {
                 ((EnvironmentAware)bean).setEnvironment(this.applicationContext.getEnvironment());
             }

             if(bean instanceof EmbeddedValueResolverAware) {
                 ((EmbeddedValueResolverAware)bean).setEmbeddedValueResolver(this.embeddedValueResolver);
             }

             if(bean instanceof ResourceLoaderAware) {
                 ((ResourceLoaderAware)bean).setResourceLoader(this.applicationContext);
             }

             if(bean instanceof ApplicationEventPublisherAware) {
                 ((ApplicationEventPublisherAware)bean).setApplicationEventPublisher(this.applicationContext);
             }

             if(bean instanceof MessageSourceAware) {
                 ((MessageSourceAware)bean).setMessageSource(this.applicationContext);
             }

             if(bean instanceof ApplicationContextAware) {
                 ((ApplicationContextAware)bean).setApplicationContext(this.applicationContext);
             }
         }

     }

2.看以上代码第9、15、19、48行可知，假若bean对象的类是ApplicationContextAware类型的话，就会调用invokeAwareInterfaces方法，然后执行第48行，将spring容器赋值给bean对象的applicationContext属性。

所以重要的实现思路来了：

　　a.Bird类实现ApplicationContextAware接口，并添加一个ApplicationContext类型的属性context，并实现ApplicationContextAware接口的方法：

 @Component
 public class Bird implements ApplicationContextAware {
     //得到管理它的Spring容器
     private ApplicationContext context;

     @Override
     public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
         this.context = applicationContext;
     }

     @Override
     public String toString() {
         return "Bird [context=" + context + "]";
     }
 }

　　b.写一个测试类，测试结果：

 public class TestMain {

     public static void main(String[] args) {
         // 1.获得Spring容器对象
         AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(ApplicationConfig.class);
         System.out.println("Spring容器 " + context);
         Bird bird = (Bird) context.getBean("bird");
         System.out.println(bird);
     }
 }

　　c.查看测试输出的结果：输出结果显示，TestMain 类的main方法中new出来的context和Bird组件的bean对象的context属性地址相同，所以Bird的bean对象得到了spring容器内容。

 "C:\Program Files\Java\jdk1.8.0_25\bin\java" -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:52099,suspend=y,server=n -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_25\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_25\jre\lib\rt.jar;D:\kaikeba_java\2018-11-28-spring-beanpostprocessor\02-项目\11_Spring_BeanPostProcessor的实现类介绍\target\test-classes;D:\kaikeba_java\2018-11-28-spring-beanpostprocessor\02-项目\11_Spring_BeanPostProcessor的实现类介绍\target\classes;D:\caowenlong\javaDevelopTool\apache-maven-3.5.3-bin\repo\org\springframework\spring-context\5.0.5.RELEASE\spring-context-5.0.5.RELEASE.jar;D:\caowenlong\javaDevelopTool\apache-maven-3.5.3-bin\repo\org\springframework\spring-aop\5.0.5.RELEASE\spring-aop-5.0.5.RELEASE.jar;D:\caowenlong\javaDevelopTool\apache-maven-3.5.3-bin\repo\org\springframework\spring-beans\5.0.5.RELEASE\spring-beans-5.0.5.RELEASE.jar;D:\caowenlong\javaDevelopTool\apache-maven-3.5.3-bin\repo\org\springframework\spring-core\5.0.5.RELEASE\spring-core-5.0.5.RELEASE.jar;D:\caowenlong\javaDevelopTool\apache-maven-3.5.3-bin\repo\org\springframework\spring-jcl\5.0.5.RELEASE\spring-jcl-5.0.5.RELEASE.jar;D:\caowenlong\javaDevelopTool\apache-maven-3.5.3-bin\repo\org\springframework\spring-expression\5.0.5.RELEASE\spring-expression-5.0.5.RELEASE.jar;D:\caowenlong\javaDevelopTool\IntelliJ IDEA 2016.2\lib\idea_rt.jar" com.kkb.test.TestMain
 Connected to the target VM, address: '127.0.0.1:52099', transport: 'socket'
 三月 26, 2019 11:26:26 上午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
 信息: Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@2ed94a8b: startup date [Tue Mar 26 11:26:26 CST 2019]; root of context hierarchy
 Spring容器 org.springframework.context.annotation.AnnotationConfigApplicationContext@2ed94a8b: startup date [Tue Mar 26 11:26:26 CST 2019]; root of context hierarchy
 Bird [context=org.springframework.context.annotation.AnnotationConfigApplicationContext@2ed94a8b: startup date [Tue Mar 26 11:26:26 CST 2019]; root of context hierarchy]
 Disconnected from the target VM, address: '127.0.0.1:52099', transport: 'socket'

 Process finished with exit code 0