Bean后置处理器 - MergedBeanDefinitionPostProcessor
创建完对象之后, 接下来, 就应该想办法对属性进行注入了, 其中就包括 @Autowired 注入
但是在注入之前, 貌似 还没有对 @Autowired 进行扫描和解析.
代码块:
if (instanceWrapper == null) { /** * 创建 bean 实例，并将实例包裹在 BeanWrapper 实现类对象中返回。 * createBeanInstance中包含三种创建 bean 实例的方式： * 1. 通过工厂方法创建 bean 实例 * 2. 通过构造方法自动注入（autowire by constructor）的方式创建 bean 实例 * 3. 通过无参构造方法方法创建 bean 实例 * * 若 bean 的配置信息中配置了 lookup-method 和 replace-method，则会使用 CGLIB 增强 bean 实例。 */ instanceWrapper = createBeanInstance(beanName, mbd, args); } final Object bean = instanceWrapper.getWrappedInstance(); Class<?> beanType = instanceWrapper.getWrappedClass(); if (beanType != NullBean.class) { mbd.resolvedTargetType = beanType; } // Allow post-processors to modify the merged bean definition. synchronized (mbd.postProcessingLock) { if (!mbd.postProcessed) { try { //调用属性合并后置处理器, 进行属性合并 //这里会进行 一些注解 的扫描 //CommonAnnotationBeanPostProcessor -> @PostConstruct @PreDestroy @Resource //AutowiredAnnotationBeanPostProcessor -> @Autowired @Value applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName); } catch (Throwable ex) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Post-processing of merged bean definition failed", ex); } mbd.postProcessed = true; } }
接着看里面的内容
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); } } }
通过调试, 可以获取, 这里满足条件的, 有三个后置处理器, 按照调用先后顺序为:
接下来看看里面都干了啥
CommonAnnotationBeanPostProcessor
这一步, 主要是扫描作用.
1. 扫描 @PostConstruct 和 @PreDestroy (这个很直观的能看到, 其无参构造函数中, 出现了这两个注解)
2. 扫描 @Resource , 这个需要到 findResourceMetadata 中, 才能看到
public CommonAnnotationBeanPostProcessor() { setOrder(Ordered.LOWEST_PRECEDENCE - 3); setInitAnnotationType(PostConstruct.class); setDestroyAnnotationType(PreDestroy.class); ignoreResourceType("javax.xml.ws.WebServiceContext"); } /** * 1.遍历扫描方法上标注了 @PostConstruct 和 @PreDestroy 注解的类 * 2.遍历扫描方法上标注了 @Resource 注解的类 * @param beanDefinition * @param beanType * @param beanName */ @Override public void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName) { super.postProcessMergedBeanDefinition(beanDefinition, beanType, beanName); InjectionMetadata metadata = findResourceMetadata(beanName, beanType, null); metadata.checkConfigMembers(beanDefinition); }
1. 调用父类方法, 进行@PostConstruct 和 @PreDestroy 扫描
org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor#postProcessMergedBeanDefinition
@Override public void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName) { LifecycleMetadata metadata = findLifecycleMetadata(beanType); metadata.checkConfigMembers(beanDefinition); }
findLifecycleMetadata最终会调用 org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor#buildLifecycleMetadata 方法
private LifecycleMetadata buildLifecycleMetadata(final Class<?> clazz) { 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<>(); ReflectionUtils.doWithLocalMethods(targetClass, method -> { 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); } } 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); } } }); initMethods.addAll(0, currInitMethods); destroyMethods.addAll(currDestroyMethods); //当前类解析完后, 拿到父类继续进行解析, 直到父类为 Object targetClass = targetClass.getSuperclass(); } while (targetClass != null && targetClass != Object.class); return new LifecycleMetadata(clazz, initMethods, destroyMethods); }
这里就是遍历类和其父类, 进行查找的.
2. 进行 @Resource 扫描
Resource 扫描, 是在本类中完成的.
org.springframework.context.annotation.CommonAnnotationBeanPostProcessor#findResourceMetadata
private InjectionMetadata findResourceMetadata(String beanName, final Class<?> clazz, @Nullable PropertyValues pvs) { // Fall back to class name as cache key, for backwards compatibility with custom callers. String cacheKey = (StringUtils.hasLength(beanName) ? beanName : clazz.getName()); // Quick check on the concurrent map first, with minimal locking. InjectionMetadata metadata = this.injectionMetadataCache.get(cacheKey); if (InjectionMetadata.needsRefresh(metadata, clazz)) { synchronized (this.injectionMetadataCache) { metadata = this.injectionMetadataCache.get(cacheKey); if (InjectionMetadata.needsRefresh(metadata, clazz)) { if (metadata != null) { metadata.clear(pvs); } metadata = buildResourceMetadata(clazz); this.injectionMetadataCache.put(cacheKey, metadata); } } } return metadata; }
这里主要看 buildResourceMetadata( ) 方法.
private InjectionMetadata buildResourceMetadata(final Class<?> clazz) { List<InjectionMetadata.InjectedElement> elements = new ArrayList<>(); Class<?> targetClass = clazz; do { final List<InjectionMetadata.InjectedElement> currElements = new ArrayList<>(); //扫描字段 ReflectionUtils.doWithLocalFields(targetClass, field -> { if (webServiceRefClass != null && field.isAnnotationPresent(webServiceRefClass)) { if (Modifier.isStatic(field.getModifiers())) { throw new IllegalStateException("@WebServiceRef annotation is not supported on static fields"); } currElements.add(new WebServiceRefElement(field, field, null)); } else if (ejbRefClass != null && field.isAnnotationPresent(ejbRefClass)) { if (Modifier.isStatic(field.getModifiers())) { throw new IllegalStateException("@EJB annotation is not supported on static fields"); } currElements.add(new EjbRefElement(field, field, null)); } else if (field.isAnnotationPresent(Resource.class)) { //静态字段上标注 @Resource , 会抛异常 if (Modifier.isStatic(field.getModifiers())) { throw new IllegalStateException("@Resource annotation is not supported on static fields"); } if (!this.ignoredResourceTypes.contains(field.getType().getName())) { currElements.add(new ResourceElement(field, field, null)); } } }); //扫描方法 ReflectionUtils.doWithLocalMethods(targetClass, method -> { Method bridgedMethod = BridgeMethodResolver.findBridgedMethod(method); if (!BridgeMethodResolver.isVisibilityBridgeMethodPair(method, bridgedMethod)) { return; } if (method.equals(ClassUtils.getMostSpecificMethod(method, clazz))) { if (webServiceRefClass != null && bridgedMethod.isAnnotationPresent(webServiceRefClass)) { if (Modifier.isStatic(method.getModifiers())) { throw new IllegalStateException("@WebServiceRef annotation is not supported on static methods"); } if (method.getParameterCount() != 1) { throw new IllegalStateException("@WebServiceRef annotation requires a single-arg method: " + method); } PropertyDescriptor pd = BeanUtils.findPropertyForMethod(bridgedMethod, clazz); currElements.add(new WebServiceRefElement(method, bridgedMethod, pd)); } else if (ejbRefClass != null && bridgedMethod.isAnnotationPresent(ejbRefClass)) { if (Modifier.isStatic(method.getModifiers())) { throw new IllegalStateException("@EJB annotation is not supported on static methods"); } if (method.getParameterCount() != 1) { throw new IllegalStateException("@EJB annotation requires a single-arg method: " + method); } PropertyDescriptor pd = BeanUtils.findPropertyForMethod(bridgedMethod, clazz); currElements.add(new EjbRefElement(method, bridgedMethod, pd)); } else if (bridgedMethod.isAnnotationPresent(Resource.class)) { if (Modifier.isStatic(method.getModifiers())) { throw new IllegalStateException("@Resource annotation is not supported on static methods"); } Class<?>[] paramTypes = method.getParameterTypes(); //如果目标方法, 没有参数, 或者有多个参数, 则抛出异常 if (paramTypes.length != 1) { throw new IllegalStateException("@Resource annotation requires a single-arg method: " + method); } if (!this.ignoredResourceTypes.contains(paramTypes[0].getName())) { //这里拿到方法名, 会去跟类中的属性进行匹配 //匹配的规则是: method.equals(pd.getReadMethod()) || method.equals(pd.getWriteMethod()) //这个 readMethod 就是 getXXX 或 isXXX, writeMethod 就是 setXXX //如果匹配不上, pd = null PropertyDescriptor pd = BeanUtils.findPropertyForMethod(bridgedMethod, clazz); currElements.add(new ResourceElement(method, bridgedMethod, pd)); } } } }); elements.addAll(0, currElements); targetClass = targetClass.getSuperclass(); } while (targetClass != null && targetClass != Object.class); return new InjectionMetadata(clazz, elements); }
注意到, 这里只进行了扫描转换工作, 并没有进行属性注入工作.
AutowiredAnnotationBeanPostProcessor
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. } } @Override public void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName) { InjectionMetadata metadata = findAutowiringMetadata(beanName, beanType, null); metadata.checkConfigMembers(beanDefinition); }
从这段代码, 可以猜测, 自动注入的类型, 是个集合, 这里有两个
1. @Autowired
2. @Value
findAutowiringMetadata() 最终会调用本类方法:
org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor#buildAutowiringMetadata
private InjectionMetadata buildAutowiringMetadata(final Class<?> clazz) { List<InjectionMetadata.InjectedElement> elements = new ArrayList<>(); //需要处理的目标类 Class<?> targetClass = clazz; do { final List<InjectionMetadata.InjectedElement> currElements = new ArrayList<>(); // 通过反射获取该类所有的字段，并遍历每一个字段，通过方法 findAutowiredAnnotation 遍历每一个字段的所用注解， // 如果用autowired修饰了，则返回 auotowired 相关属性 ReflectionUtils.doWithLocalFields(targetClass, field -> { AnnotationAttributes ann = findAutowiredAnnotation(field); if (ann != null) { // 校验autowired注解是否用在了static方法上 if (Modifier.isStatic(field.getModifiers())) { if (logger.isInfoEnabled()) { logger.info("Autowired annotation is not supported on static fields: " + field); } return; } boolean required = determineRequiredStatus(ann); currElements.add(new AutowiredFieldElement(field, required)); } }); //通过反射处理类的method ReflectionUtils.doWithLocalMethods(targetClass, method -> { Method bridgedMethod = BridgeMethodResolver.findBridgedMethod(method); if (!BridgeMethodResolver.isVisibilityBridgeMethodPair(method, bridgedMethod)) { return; } AnnotationAttributes ann = findAutowiredAnnotation(bridgedMethod); if (ann != null && method.equals(ClassUtils.getMostSpecificMethod(method, clazz))) { if (Modifier.isStatic(method.getModifiers())) { if (logger.isInfoEnabled()) { logger.info("Autowired annotation is not supported on static methods: " + method); } return; } if (method.getParameterCount() == 0) { if (logger.isInfoEnabled()) { logger.info("Autowired annotation should only be used on methods with parameters: " + method); } } boolean required = determineRequiredStatus(ann); //这里也会进行属性的匹配, 按照规则 : method.equals(pd.getReadMethod()) || method.equals(pd.getWriteMethod()) //如果匹配不上, pd = null PropertyDescriptor pd = BeanUtils.findPropertyForMethod(bridgedMethod, clazz); currElements.add(new AutowiredMethodElement(method, required, pd)); } }); //用@Autowired修饰的注解可能不止一个，因此都加在 elements 这个容器里面，一起处理 elements.addAll(0, currElements); targetClass = targetClass.getSuperclass(); } while (targetClass != null && targetClass != Object.class); return new InjectionMetadata(clazz, elements); }
这里也只是进行了扫描, 没有进行属性注入工作.
ApplicationListenerDetector
@Override public void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName) { this.singletonNames.put(beanName, beanDefinition.isSingleton()); }
这个类也是挺能凑热闹的. 这里没有进行任何扫描工作. 只是记录了容器中的 bean 是否是单例模式.
这里记录这个标志, 是为了后面用的. 对监听器进行过滤用的.
