web九大组件之---RequestMappingHandlerAdapter详尽解析【享学Spring MVC】（上）

// @since 3.1 实现了InitializingBean接口和BeanFactoryAware
public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter implements BeanFactoryAware, InitializingBean {
  // 唯一构造方法：默认注册一些消息转换器。
  // 开启@EnableWebMvc后此默认行为会被setMessageConverters()方法覆盖
  public RequestMappingHandlerAdapter() {
    StringHttpMessageConverter stringHttpMessageConverter = new StringHttpMessageConverter();
    stringHttpMessageConverter.setWriteAcceptCharset(false);  // see SPR-7316
    this.messageConverters = new ArrayList<>(4);
    this.messageConverters.add(new ByteArrayHttpMessageConverter());
    this.messageConverters.add(stringHttpMessageConverter);
    try {
      this.messageConverters.add(new SourceHttpMessageConverter<>());
    } catch (Error err) {
      // Ignore when no TransformerFactory implementation is available
    }
    this.messageConverters.add(new AllEncompassingFormHttpMessageConverter());
  }
  // 此方法在此Bean初始化的时候会执行：扫描解析容器内的@ControllerAdvice...
  // 方法体看起来代码不多，但其实每个方法内部，都可谓是个庞然大物，请详细观察理解~~~~
  @Override
  public void afterPropertiesSet() {
    // Do this first, it may add ResponseBody advice beans
    // 详见下面的解释分析
    initControllerAdviceCache();
    // 这三大部分，可是 "参数自动组装" 相关的组件~~~~每一份都非常的重要
    if (this.argumentResolvers == null) {
      List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
      this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
    }
    if (this.initBinderArgumentResolvers == null) {
      List<HandlerMethodArgumentResolver> resolvers = getDefaultInitBinderArgumentResolvers();
      this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
    }
    if (this.returnValueHandlers == null) {
      List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
      this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
    }
  }
}

RequestMappingHandlerAdapter：
// ======================相关成员变量======================
// 装载RequestBodyAdvice和ResponseBodyAdvice的实现类们~
private List<Object> requestResponseBodyAdvice = new ArrayList<>();
// MethodIntrospector.selectMethods的过滤器。
// 这里意思是：含有@ModelAttribute，但是但是但是不含有@RequestMapping注解的方法~~~~~
public static final MethodFilter MODEL_ATTRIBUTE_METHODS = method -> (!AnnotatedElementUtils.hasAnnotation(method, RequestMapping.class) && AnnotatedElementUtils.hasAnnotation(method, ModelAttribute.class));
// 标注了注解@InitBinder的方法~~~
public static final MethodFilter INIT_BINDER_METHODS = method -> AnnotatedElementUtils.hasAnnotation(method, InitBinder.class);
// 存储标注了@ModelAttribute注解的方法的缓存~~~~
private final Map<ControllerAdviceBean, Set<Method>> modelAttributeAdviceCache = new LinkedHashMap<>();
// 存储标注了@InitBinder注解的方法的缓存~~~~
private final Map<ControllerAdviceBean, Set<Method>> initBinderAdviceCache = new LinkedHashMap<>();
  private void initControllerAdviceCache() {
    if (getApplicationContext() == null) {
      return;
    }
    // 拿到容器内所有的标注有@ControllerAdvice的组件们
    // BeanFactoryUtils.beanNamesForTypeIncludingAncestors(context, Object.class)
    // .filter(name -> context.findAnnotationOnBean(name, ControllerAdvice.class) != null)
    // .map(name -> new ControllerAdviceBean(name, context)) // 使用ControllerAdviceBean包装起来，持有name的引用（还木实例化哟）
    // .collect(Collectors.toList());
    // 因为@ControllerAdvice注解可以指定包名等属性，具体可参见HandlerTypePredicate的判断逻辑，是否生效
    // 注意：@RestControllerAdvice是@ControllerAdvice和@ResponseBody的结合体，所以此处也会被找出来
    // 最后Ordered排序
    List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());
    AnnotationAwareOrderComparator.sort(adviceBeans);
    // 临时存储RequestBodyAdvice和ResponseBodyAdvice的实现类
    // 它哥俩是必须配合@ControllerAdvice一起使用的~
    List<Object> requestResponseBodyAdviceBeans = new ArrayList<>();
    for (ControllerAdviceBean adviceBean : adviceBeans) {
      Class<?> beanType = adviceBean.getBeanType();
      if (beanType == null) {
        throw new IllegalStateException("Unresolvable type for ControllerAdviceBean: " + adviceBean);
      }
      // 又见到了这个熟悉的方法selectMethods~~~~过滤器请参照成员变量
      // 含有@ModelAttribute，但是但是但是不含有@RequestMapping注解的方法~~~~~  找到之后放在全局变量缓存起来
      // 简单的说就是找到@ControllerAdvice里面所有的@ModelAttribute方法们
      Set<Method> attrMethods = MethodIntrospector.selectMethods(beanType, MODEL_ATTRIBUTE_METHODS);
      if (!attrMethods.isEmpty()) {
        this.modelAttributeAdviceCache.put(adviceBean, attrMethods);
      }
      // 找标注了注解@InitBinder的方法~~~（和有没有@RequestMapping木有关系了~~~）
      // 找到@ControllerAdvice里面所有的@InitBinder方法们
      Set<Method> binderMethods = MethodIntrospector.selectMethods(beanType, INIT_BINDER_METHODS);
      if (!binderMethods.isEmpty()) {
        this.initBinderAdviceCache.put(adviceBean, binderMethods);
      }
      // 这两个接口是Spring4.1 4.2提供的，实现了这两个接口的 
      // 此处先放在requestResponseBodyAdviceBeans里面装着 最后放到全局缓存requestResponseBodyAdvice里面去
      if (RequestBodyAdvice.class.isAssignableFrom(beanType) || ResponseBodyAdvice.class.isAssignableFrom(beanType)) {
        requestResponseBodyAdviceBeans.add(adviceBean);
      }
    }
    // 这个意思是，放在该list的头部。
    // 因为requestResponseBodyAdvice有可能通过set方法进来已经有值了~~~所以此处放在头部
    if (!requestResponseBodyAdviceBeans.isEmpty()) {
      this.requestResponseBodyAdvice.addAll(0, requestResponseBodyAdviceBeans);
    }
    // 输出debug日志...略（debug日志哦~）
    if (logger.isDebugEnabled()) {
      ...
    }
  }

  @Override
  public void afterPropertiesSet() {
    ...
    // 初始化参数解析器
    if (this.argumentResolvers == null) {
      List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
      this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
    }
    // 初始化@InitBinder的参数解析器
    if (this.initBinderArgumentResolvers == null) {
      List<HandlerMethodArgumentResolver> resolvers = getDefaultInitBinderArgumentResolvers();
      this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
    }
    // 初始化返回值解析器
    if (this.returnValueHandlers == null) {
      List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
      this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
    }
  }