spring源码之注解收集

实例化完成后接下来就需要对类中的属性进行依赖注入操作，类里面属性和方法的依赖注入一般用@Autowired或者@Resource 注解，核心方法为applyMergedBeanDefinitionPostProcessors

protected void applyMergedBeanDefinitionPostProcessors(RootBeanDefinition mbd, Class<?> beanType, String beanName) {
	for (BeanPostProcessor bp : getBeanPostProcessors()) {
		if (bp instanceof MergedBeanDefinitionPostProcessor) {
			MergedBeanDefinitionPostProcessor bdp = (MergedBeanDefinitionPostProcessor) bp;
			bdp.postProcessMergedBeanDefinition(mbd, beanType, beanName);
		}
	}
}

也是beanPostProcessor接口的典型运用

CommonAnnotationBeanPostProcessor：
支持了@PostConstruct@PreDestroy,@Resource注解

AutowiredAnnotationBeanPostProcessor：
支持 @Autowired,@Value注解

一、CommonAnnotationBeanPostProcessor注解的收集

//到父类中取标记这两个注解的类
public CommonAnnotationBeanPostProcessor() {
		setOrder(Ordered.LOWEST_PRECEDENCE - 3);
		setInitAnnotationType(PostConstruct.class);
		setDestroyAnnotationType(PreDestroy.class);
		ignoreResourceType("javax.xml.ws.WebServiceContext");
}


@Override
public void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName) {
	//扫描@PostConstruct@PreDestroy
	super.postProcessMergedBeanDefinition(beanDefinition, beanType, beanName);
	//扫描方法或属性上是否有@Resource注解，有就收集起来封装成对象
	InjectionMetadata metadata = findResourceMetadata(beanName, beanType, null);
	metadata.checkConfigMembers(beanDefinition);
}

//扫描@PostConstruct@PreDestroy，如果缓存为空，则走此方法
private LifecycleMetadata buildLifecycleMetadata(final Class<?> clazz) {
		if (!AnnotationUtils.isCandidateClass(clazz, Arrays.asList(this.initAnnotationType, this.destroyAnnotationType))) {
			return this.emptyLifecycleMetadata;
		}

		List<LifecycleElement> initMethods = new ArrayList<>();
		List<LifecycleElement> destroyMethods = new ArrayList<>();
		Class<?> targetClass = clazz;

		do {
			final List<LifecycleElement> currInitMethods = new ArrayList<>();
			final List<LifecycleElement> currDestroyMethods = new ArrayList<>();
			//遍历类中所有的方法
			ReflectionUtils.doWithLocalMethods(targetClass, method -> {
				//判断有没有@PostConstruct，有则加入到集合中
				if (this.initAnnotationType != null && method.isAnnotationPresent(this.initAnnotationType)) {
					LifecycleElement element = new LifecycleElement(method);
					currInitMethods.add(element);
					if (logger.isTraceEnabled()) {
						logger.trace("Found init method on class [" + clazz.getName() + "]: " + method);
					}
				}
				//判断有没有@PreDestroy，有则加入到集合中
				if (this.destroyAnnotationType != null && method.isAnnotationPresent(this.destroyAnnotationType)) {
					currDestroyMethods.add(new LifecycleElement(method));
					if (logger.isTraceEnabled()) {
						logger.trace("Found destroy method on class [" + clazz.getName() + "]: " + method);
					}
				}
			});
			//加入初始化和销毁方法
			initMethods.addAll(0, currInitMethods);
			destroyMethods.addAll(currDestroyMethods);
			targetClass = targetClass.getSuperclass();
		}
		while (targetClass != null && targetClass != Object.class);

		return (initMethods.isEmpty() && destroyMethods.isEmpty() ? this.emptyLifecycleMetadata :
				new LifecycleMetadata(clazz, initMethods, destroyMethods));
}

获取@Resource注解的逻辑和上面差不多，从类中获取所有 Field 对象，循环 field 对象，判断 field 有没有@Resource 注解，如果有注解封装
成 ResourceElement，获取Method对象一样，最终把两个 field 和 Method 封装的对象集合封装到 InjectionMetadata 对象的injectedElements属性中。

二、AutowiredAnnotationBeanPostProcessor注解的收集：

//定义收集的注解@Autowired和@Value
public AutowiredAnnotationBeanPostProcessor() {
		this.autowiredAnnotationTypes.add(Autowired.class);
		this.autowiredAnnotationTypes.add(Value.class);
		try {
			this.autowiredAnnotationTypes.add((Class<? extends Annotation>)
					ClassUtils.forName("javax.inject.Inject", AutowiredAnnotationBeanPostProcessor.class.getClassLoader()));
			logger.trace("JSR-330 'javax.inject.Inject' annotation found and supported for autowiring");
		}
		catch (ClassNotFoundException ex) {
			// JSR-330 API not available - simply skip.
		}
	}