1. aware接口的作用
通过aware接口可以获取Spring容器相关信息，但这样会与Spring容器耦合。
2. 常用aware接口及作用
执行顺序从上到下。
| 类名 | 作用 |
|---|---|
| BeanNameAware | 获得容器中bean名称 |
| BeanClassLoaderAware | 获得类加载器 |
| BeanFactoryAware | 获得bean创建工厂 |
| EnvironmentAware | 获得环境变量 |
| EmbeddedValueResolverAware | 获取spring容器加载的properties文件属性值 |
| ResourceLoaderAware | 获得资源加载器 |
| ApplicationEventPublisherAware | 获得应用事件发布器 |
| MessageSourceAware | 获得文本信息 |
| ApplicationContextAware | 获得当前应用上下文 |
3. 使用样例：ApplicationContextAware 在Bean中获取上下文
@Component("springUtil")
public final class SpringUtil implements ApplicationContextAware {
private static ApplicationContext applicationContext;
@Override
public void setApplicationContext(@NonNull ApplicationContext applicationContext) {
synchronized (SpringUtil.class) {
if (null == SpringUtil.applicationContext) {
SpringUtil.applicationContext = applicationContext;
}
}
}
public static Object getBean(String name) {
return getApplicationContext().getBean(name);
}
private static ApplicationContext getApplicationContext() {
return applicationContext;
}
public static <T> T getBean(Class<T> clazz) {
return getApplicationContext().getBean(clazz);
}
public static <T> T getBean(String name, Class<T> clazz) {
return getApplicationContext().getBean(name, clazz);
}
}
4. 自定义aware的方式
先定义一个继承Aware的接口，然后注册一个实现BeanPostProcessor接口的Bean，在postProcessBeforeInitialization中处理Aware接口的逻辑。
举一个例子。获取调用自定义Aware接口方法的时间。
4.1 定义继承Aware的接口
public interface TimeAware extends Aware {
void setTriggerTime(Date date);
}4.2 注册实现BeanPostProcessor接口的Bean
@Component
public class AwarePostProcessor implements BeanPostProcessor {
private final ConfigurableApplicationContext applicationContext;
public AwarePostProcessor(ConfigurableApplicationContext applicationContext) {
this.applicationContext = applicationContext;
}
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
if (bean instanceof Aware) {
if (bean instanceof TimeAware) {
// 实现自定义Aware接口的逻辑，设置调用的时间
((TimeAware)bean).setTriggerTime(new Date());
}
}
return bean;
}
}
4.3 实现TimeAware接口，并测试
@Import(AwarePostProcessor.class)
public class Test implements TimeAware {
Date date;
@Override
public void setTriggerTime(Date date) {
this.date = date;
}
public static void main(String[] args) {
ApplicationContext context = new AnnotationConfigApplicationContext(Test.class);
Test bean = context.getBean(Test.class);
System.out.println(bean.date);
}
}
结果：
5. 源码处理方式
- Bean实例化->填充属性->初始化，在初始化阶段将实现aware接口的Bean的方法执行。
1.先执行实现了下面三个aware接口的方法
- BeanNameAware
- BeanClassLoaderAware
- BeanFactoryAware
2.调用初始化方法
3.执行实现剩下aware接口的方法
5.1 初始化阶段的源码逻辑
AbstractAutowireCapableBeanFactory#initializeBean
protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
invokeAwareMethods(beanName, bean);
return null;
}, getAccessControlContext());
}
else {
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
// 此处会调用ApplicationContextAwareProcessor执行其他的aware方法.
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
throw new BeanCreationException(
(mbd != null ? mbd.getResourceDescription() : null),
beanName, "Invocation of init method failed", ex);
}
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
5.2 实现前三个aware接口的处理
调用initializeBean =>invokeAwareMethods方法将前三个aware方法调用
AbstractAutowireCapableBeanFactory#invokeAwareMethods
private void invokeAwareMethods(String beanName, Object bean) {
if (bean instanceof Aware) {
if (bean instanceof BeanNameAware) {
((BeanNameAware) bean).setBeanName(beanName);
}
if (bean instanceof BeanClassLoaderAware) {
ClassLoader bcl = getBeanClassLoader();
if (bcl != null) {
((BeanClassLoaderAware) bean).setBeanClassLoader(bcl);
}
}
if (bean instanceof BeanFactoryAware) {
((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
}
}
}
5.3 剩余实现aware接口的Bean的处理
调用initializeBean =>applyBeanPostProcessorsBeforeInitialization=>BeanPostProcessor.postProcessBeforeInitialization
进入ApplicationContextAwareProcessor#postProcessBeforeInitialization=>invokeAwareInterfaces
private void invokeAwareInterfaces(Object bean) {
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);
}
}
因此可以自定义aware接口，并且注册一个实现BeanPostProcessor的postProcessBeforeInitialization方法的Bean，处理调用aware方法时的处理逻辑。
