【Spring源码分析】16-AutowiredAnnotationBeanPostProcessor

AutowiredAnnotationBeanPostProcessor继承了InstantiationAwareBeanPostProcessorAdapter间接实现了SmartInstantiationAwareBeanPostProcessor接口覆盖了determineCandidateConstructors()方法,此方法在实例化bean前选取一个构造方法数组,请参考bean创建的流程https://blog.csdn.net/shenchaohao12321/article/details/80441204https://blog.csdn.net/shenchaohao12321/article/details/80535708

先看determineCandidateConstructors()方法的前一小段是处理@Lookup注解的。

if (!this.lookupMethodsChecked.contains(beanName)) {
   try {
      ReflectionUtils.doWithMethods(beanClass, method -> {
         Lookup lookup = method.getAnnotation(Lookup.class);
         if (lookup != null) {
            Assert.state(beanFactory != null, "No BeanFactory available");
            LookupOverride override = new LookupOverride(method, lookup.value());
            try {
               RootBeanDefinition mbd = (RootBeanDefinition) beanFactory.getMergedBeanDefinition(beanName);
               mbd.getMethodOverrides().addOverride(override);
            }
            catch (NoSuchBeanDefinitionException ex) {
               throw new BeanCreationException(beanName,
                  "Cannot apply @Lookup to beans without corresponding bean definition");
            }
         }
      });
   }
   catch (IllegalStateException ex) {
      throw new BeanCreationException(beanName, "Lookup method resolution failed", ex);
   }
   this.lookupMethodsChecked.add(beanName);
}

将beanClass被@Lookup标记的方法封装到LookupOverride中,通过mbd.getMethodOverrides().addOverride(override)加入到BeanDefinition中,后面会在AbstractAutowireCapableBeanFactory的instantiateBean()方法中,会使用CglibSubclassingInstantiationStrategy的instantiate()方法创建bean对象。

@Override
public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner) {
   // Don't override the class with CGLIB if no overrides.
   if (!bd.hasMethodOverrides()) {
      Constructor<?> constructorToUse;
      synchronized (bd.constructorArgumentLock) {
         constructorToUse = (Constructor<?>) bd.resolvedConstructorOrFactoryMethod;
         if (constructorToUse == null) {
            final Class<?> clazz = bd.getBeanClass();
            if (clazz.isInterface()) {
               throw new BeanInstantiationException(clazz, "Specified class is an interface");
            }
            try {
               if (System.getSecurityManager() != null) {
                  constructorToUse = AccessController.doPrivileged(
                        (PrivilegedExceptionAction<Constructor<?>>) clazz::getDeclaredConstructor);
               }
               else {
                  constructorToUse = clazz.getDeclaredConstructor();
               }
               bd.resolvedConstructorOrFactoryMethod = constructorToUse;
            }
            catch (Throwable ex) {
               throw new BeanInstantiationException(clazz, "No default constructor found", ex);
            }
         }
      }
      return BeanUtils.instantiateClass(constructorToUse);
   }
   else {
      // Must generate CGLIB subclass.
      return instantiateWithMethodInjection(bd, beanName, owner);
   }
}

可以看到如果!bd.hasMethodOverrides()则走instantiateWithMethodInjection()方法,这个方法内使用了CglibSubclassingInstantiationStrategy内部类CglibSubclassCreator来创建cglib的代理对象。CglibSubclassCreator使用的callback拦截器就包含LookupOverrideMethodInterceptor。

private static class LookupOverrideMethodInterceptor extends CglibIdentitySupport implements MethodInterceptor {

   private final BeanFactory owner;

   public LookupOverrideMethodInterceptor(RootBeanDefinition beanDefinition, BeanFactory owner) {
      super(beanDefinition);
      this.owner = owner;
   }

   @Override
   public Object intercept(Object obj, Method method, Object[] args, MethodProxy mp) throws Throwable {
      // Cast is safe, as CallbackFilter filters are used selectively.
      LookupOverride lo = (LookupOverride) getBeanDefinition().getMethodOverrides().getOverride(method);
      Assert.state(lo != null, "LookupOverride not found");
      Object[] argsToUse = (args.length > 0 ? args : null);  // if no-arg, don't insist on args at all
      if (StringUtils.hasText(lo.getBeanName())) {
         return (argsToUse != null ? this.owner.getBean(lo.getBeanName(), argsToUse) :
               this.owner.getBean(lo.getBeanName()));
      }
      else {
         return (argsToUse != null ? this.owner.getBean(method.getReturnType(), argsToUse) :
               this.owner.getBean(method.getReturnType()));
      }
   }
}

如果调用的方法是被标记的,如果配置了@Lookup的value属性则从BeanFactory中取出bean name为@Lookup的value属性的bean对象返回,否则根据方法的返回类型从BeanFactory中取出相应的bean对象。

以上就是@Lookup的处理过程。

determineCandidateConstructors()方法的剩余部分就是挑选出候选的构造方法,从所有声明的构造方法选取带有@Autowired注解的,但是@Autowired的required==true的只能有一个,如果还有无参构造方法,再加上无参构造方法。

一个bean实例创建之后但此时还没有调用populateBean()方法完成属性的填充时,会经历MergedBeanDefinitionPostProcessor的postProcessMergedBeanDefinition()方法。

@Override
public void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName) {
   InjectionMetadata metadata = findAutowiringMetadata(beanName, beanType, null);
   metadata.checkConfigMembers(beanDefinition);
}
private InjectionMetadata findAutowiringMetadata(String beanName, 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 = buildAutowiringMetadata(clazz);
            this.injectionMetadataCache.put(cacheKey, metadata);
         }
      }
   }
   return metadata;
}

injectionMetadataCache是一个Map对象,缓存beanName与InjectionMetadata。InjectionMetadata对象通过buildAutowiringMetadata()方法来创建的。

private InjectionMetadata buildAutowiringMetadata(final Class<?> clazz) {
   LinkedList<InjectionMetadata.InjectedElement> elements = new LinkedList<>();
   Class<?> targetClass = clazz;
   do {
      final LinkedList<InjectionMetadata.InjectedElement> currElements = new LinkedList<>();
      ReflectionUtils.doWithLocalFields(targetClass, field -> {
         AnnotationAttributes ann = findAutowiredAnnotation(field);
         if (ann != null) {
            if (Modifier.isStatic(field.getModifiers())) {
               if (logger.isWarnEnabled()) {
                  logger.warn("Autowired annotation is not supported on static fields: " + field);
               }
               return;
            }
            boolean required = determineRequiredStatus(ann);
            currElements.add(new AutowiredFieldElement(field, required));
         }
      });

      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.isWarnEnabled()) {
                  logger.warn("Autowired annotation is not supported on static methods: " + method);
               }
               return;
            }
            if (method.getParameterCount() == 0) {
               if (logger.isWarnEnabled()) {
                  logger.warn("Autowired annotation should only be used on methods with parameters: " +
                        method);
               }
            }
            boolean required = determineRequiredStatus(ann);
            PropertyDescriptor pd = BeanUtils.findPropertyForMethod(bridgedMethod, clazz);
            currElements.add(new AutowiredMethodElement(method, required, pd));
         }
      });
      elements.addAll(0, currElements);
      targetClass = targetClass.getSuperclass();
   }
   while (targetClass != null && targetClass != Object.class);

   return new InjectionMetadata(clazz, elements);
}

buildAutowiringMetadata()方法分为对字段与方法的@Autowired(@Value,@Inject)注解处理。将标记@Autowired的字段封装为AutowiredFieldElement对象,将标记@Autowired的方法并且此方法是字段的getter或writter方法封装到AutowiredMethodElement对象然后都加入到InjectionMetadata中,此过程是一个循环过程此类处理完会沿着父类继续向上处理。AutowiredFieldElement与AutowiredMethodElement都是InjectionMetadata.InjectedElement的子类,都覆盖了父类的inject()方法这个下面会介绍。

通过findAutowiringMetadata()方法得到了InjectionMetadata对象之后调用了给对象的checkConfigMembers()方法。这个方法就是将上面保存的InjectedElement对象筛选出那些不存在于beanDefinition中的赋值给checkedElements。

public void checkConfigMembers(RootBeanDefinition beanDefinition) {
   Set<InjectedElement> checkedElements = new LinkedHashSet<>(this.injectedElements.size());
   for (InjectedElement element : this.injectedElements) {
      Member member = element.getMember();
      if (!beanDefinition.isExternallyManagedConfigMember(member)) {
         beanDefinition.registerExternallyManagedConfigMember(member);
         checkedElements.add(element);
         if (logger.isDebugEnabled()) {
            logger.debug("Registered injected element on class [" + this.targetClass.getName() + "]: " + element);
         }
      }
   }
   this.checkedElements = checkedElements;
}

到这为止就是postProcessMergedBeanDefinition()方法的全部实现逻辑并没有做什么实际事情,其实是为了后面的行为做铺垫,请看postProcessPropertyValues()方法,此方法是在属性填充阶段被调用的。

@Override
public PropertyValues postProcessPropertyValues(
      PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeanCreationException {

   InjectionMetadata metadata = findAutowiringMetadata(beanName, bean.getClass(), pvs);
   try {
      metadata.inject(bean, beanName, pvs);
   }
   catch (BeanCreationException ex) {
      throw ex;
   }
   catch (Throwable ex) {
      throw new BeanCreationException(beanName, "Injection of autowired dependencies failed", ex);
   }
   return pvs;
}

首先调用 findAutowiringMetadata()方法从缓存中再次取到InjectionMetadata对象,调用inject()方法完成autowired注入。

public void inject(Object target, @Nullable String beanName, @Nullable PropertyValues pvs) throws Throwable {
   Collection<InjectedElement> checkedElements = this.checkedElements;
   Collection<InjectedElement> elementsToIterate =
         (checkedElements != null ? checkedElements : this.injectedElements);
   if (!elementsToIterate.isEmpty()) {
      boolean debug = logger.isDebugEnabled();
      for (InjectedElement element : elementsToIterate) {
         if (debug) {
            logger.debug("Processing injected element of bean '" + beanName + "': " + element);
         }
         element.inject(target, beanName, pvs);
      }
   }
}

因为之前已经把类@Autowired注解标记的字段或方法封装到了响应的InjectedElement子类中了,此时依次调用子类的inject()方法完成对象的注入,下面分别看一看这两种注入的实现。

AutowiredFieldElement,调用BeanFactory的resolveDependency()方法返回一个符合字段类型的bean对象设置到此bean上。

@Override
protected void inject(Object bean, @Nullable String beanName, @Nullable PropertyValues pvs) throws Throwable {
   Field field = (Field) this.member;
   Object value;
   if (this.cached) {
      value = resolvedCachedArgument(beanName, this.cachedFieldValue);
   }
   else {
      DependencyDescriptor desc = new DependencyDescriptor(field, this.required);
      desc.setContainingClass(bean.getClass());
      Set<String> autowiredBeanNames = new LinkedHashSet<>(1);
      Assert.state(beanFactory != null, "No BeanFactory available");
      TypeConverter typeConverter = beanFactory.getTypeConverter();
      try {
         value = beanFactory.resolveDependency(desc, beanName, autowiredBeanNames, typeConverter);
      }
      catch (BeansException ex) {
         throw new UnsatisfiedDependencyException(null, beanName, new InjectionPoint(field), ex);
      }
      synchronized (this) {
         if (!this.cached) {
            if (value != null || this.required) {
               this.cachedFieldValue = desc;
               registerDependentBeans(beanName, autowiredBeanNames);
               if (autowiredBeanNames.size() == 1) {
                  String autowiredBeanName = autowiredBeanNames.iterator().next();
                  if (beanFactory.containsBean(autowiredBeanName) &&
                        beanFactory.isTypeMatch(autowiredBeanName, field.getType())) {
                     this.cachedFieldValue = new ShortcutDependencyDescriptor(
                           desc, autowiredBeanName, field.getType());
                  }
               }
            }
            else {
               this.cachedFieldValue = null;
            }
            this.cached = true;
         }
      }
   }
   if (value != null) {
      ReflectionUtils.makeAccessible(field);
      field.set(bean, value);
   }
}

AutowiredMethodElement,类似通过setter方法完成属性的注入。

@Override
protected void inject(Object bean, @Nullable String beanName, @Nullable PropertyValues pvs) throws Throwable {
   if (checkPropertySkipping(pvs)) {
      return;
   }
   Method method = (Method) this.member;
   Object[] arguments;
   if (this.cached) {
      // Shortcut for avoiding synchronization...
      arguments = resolveCachedArguments(beanName);
   }
   else {
      Class<?>[] paramTypes = method.getParameterTypes();
      arguments = new Object[paramTypes.length];
      DependencyDescriptor[] descriptors = new DependencyDescriptor[paramTypes.length];
      Set<String> autowiredBeans = new LinkedHashSet<>(paramTypes.length);
      Assert.state(beanFactory != null, "No BeanFactory available");
      TypeConverter typeConverter = beanFactory.getTypeConverter();
      for (int i = 0; i < arguments.length; i++) {
         MethodParameter methodParam = new MethodParameter(method, i);
         DependencyDescriptor currDesc = new DependencyDescriptor(methodParam, this.required);
         currDesc.setContainingClass(bean.getClass());
         descriptors[i] = currDesc;
         try {
            Object arg = beanFactory.resolveDependency(currDesc, beanName, autowiredBeans, typeConverter);
            if (arg == null && !this.required) {
               arguments = null;
               break;
            }
            arguments[i] = arg;
         }
         catch (BeansException ex) {
            throw new UnsatisfiedDependencyException(null, beanName, new InjectionPoint(methodParam), ex);
         }
      }
      synchronized (this) {
         if (!this.cached) {
            if (arguments != null) {
               Object[] cachedMethodArguments = new Object[paramTypes.length];
               System.arraycopy(descriptors, 0, cachedMethodArguments, 0, arguments.length);
               registerDependentBeans(beanName, autowiredBeans);
               if (autowiredBeans.size() == paramTypes.length) {
                  Iterator<String> it = autowiredBeans.iterator();
                  for (int i = 0; i < paramTypes.length; i++) {
                     String autowiredBeanName = it.next();
                     if (beanFactory.containsBean(autowiredBeanName) &&
                           beanFactory.isTypeMatch(autowiredBeanName, paramTypes[i])) {
                        cachedMethodArguments[i] = new ShortcutDependencyDescriptor(
                              descriptors[i], autowiredBeanName, paramTypes[i]);
                     }
                  }
               }
               this.cachedMethodArguments = cachedMethodArguments;
            }
            else {
               this.cachedMethodArguments = null;
            }
            this.cached = true;
         }
      }
   }
   if (arguments != null) {
      try {
         ReflectionUtils.makeAccessible(method);
         method.invoke(bean, arguments);
      }
      catch (InvocationTargetException ex){
         throw ex.getTargetException();
      }
   }
}

 

    原文作者:Spring Boot
    原文地址: https://blog.csdn.net/shenchaohao12321/article/details/81018172
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