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spring MVC源码探索之AbstractHandlerMethodMapping
AbstractHandlerMethodMapping 是什么
解释是这样的。
/**

  • Abstract base class for {@link HandlerMapping} implementations that define
  • a mapping between a request and a {@link HandlerMethod}.
    *
  • <p>For each registered handler method, a unique mapping is maintained with
  • subclasses defining the details of the mapping type {@code <T>}.
  • @param <T> The mapping for a {@link HandlerMethod} containing the conditions
  • needed to match the handler method to incoming request.
    */

public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMapping implements InitializingBean
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我的理解为AbstractHandlerMethodMapping为每个注册的handler method，对于每个子类映射类型都保护着其唯一的一个映射，就是保护handler method 和URL的关系。次要用于@Controller,@RequestMapping 等注解
AbstractHandlerMethodMapping 实现了InitializingBean接口，InitializingBean是在程序启动的时候执行其唯一的afterPropertiesSet()方法，那咱们就先看一下启动时候的要做哪些操作。
initHandlerMethods()
/**

  在初始化的时候发现 handler methods* Detects handler methods at initialization. */@Overridepublic void afterPropertiesSet() {    initHandlerMethods();}

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在我的项目启动时会执行initHandlerMethods方法，它的次要功能是扫描利用上下文，发现并注册handler methods。
/**

  • Scan beans in the ApplicationContext, detect and register handler methods.
  • @see #isHandler(Class)
  • @see #getMappingForMethod(Method, Class)
  • @see #handlerMethodsInitialized(Map)
    */

protected void initHandlerMethods() {

    if (logger.isDebugEnabled()) {            logger.debug("Looking for request mappings in application context: " + getApplicationContext());    }    // 获取IOC容器中所有bean    String[] beanNames = (this.detectHandlerMethodsInAncestorContexts ?                    BeanFactoryUtils.beanNamesForTypeIncludingAncestors(obtainApplicationContext(), Object.class) :                    obtainApplicationContext().getBeanNamesForType(Object.class));    for (String beanName : beanNames) {            if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {                    Class<?> beanType = null;                    try {                            beanType = obtainApplicationContext().getType(beanName);                    }                    catch (Throwable ex) {                            // An unresolvable bean type, probably from a lazy bean - let's ignore it.                            if (logger.isDebugEnabled()) {                                    logger.debug("Could not resolve target class for bean with name '" + beanName + "'", ex);                            }                    }                    // 判断bean 是否有Controller 注解或者RequestMapping 注解                    if (beanType != null && isHandler(beanType)) {                            detectHandlerMethods(beanName);                    }            }    }    handlerMethodsInitialized(getHandlerMethods());

}
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isHandler()
AbstractHandlerMethodMapping#isHandler()
RequestMappingHandlerMapping 是目前为止AbstractHandlerMethodMapping的子类中唯一实现了isHandler()方法的子类，看下实现
protected boolean isHandler(Class<?> beanType) {

    return (AnnotatedElementUtils.hasAnnotation(beanType, Controller.class) ||            AnnotatedElementUtils.hasAnnotation(beanType, RequestMapping.class));}

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isHandler()方法在这里的作用就是查看beanType是否有@Controller或@RequestMapping注解，这两个注解常常使用，应该都很熟悉了。
detectHandlerMethods()
AbstractHandlerMethodMapping#detectHandlerMethods() 这个方法的作用是从handler中获取handler method并注册
protected void detectHandlerMethods(final Object handler) {

    Class<?> handlerType = (handler instanceof String ?                    obtainApplicationContext().getType((String) handler) : handler.getClass());    if (handlerType != null) {            //为给定的类返回用户定义的类:通常只是给定的类，如果是cglib生成的子类，则返回原始的类。            final Class<?> userType = ClassUtils.getUserClass(handlerType);            Map<Method, T> methods = MethodIntrospector.selectMethods(userType,                            (MethodIntrospector.MetadataLookup<T>) method -> {                                    try {                                            // 为处理程序方法提供映射                                            return getMappingForMethod(method, userType);                                    }                                    catch (Throwable ex) {                                            throw new IllegalStateException("Invalid mapping on handler class [" +                                                            userType.getName() + "]: " + method, ex);                                    }                            });            if (logger.isDebugEnabled()) {                    logger.debug(methods.size() + " request handler methods found on " + userType + ": " + methods);            }            // 为查找到的handler method 进行注册            methods.forEach((method, mapping) -> {                    Method invocableMethod = AopUtils.selectInvocableMethod(method, userType);                    registerHandlerMethod(handler, invocableMethod, mapping);            });    }}

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registerHandlerMethod()
AbstractHandlerMethodMapping#registerHandlerMethod() 的作用是为每个handler method注册它们唯一的映射路径，源码如下：
/**

  • Register a handler method and its unique mapping. Invoked at startup for
  • each detected handler method.
  • @param handler the bean name of the handler or the handler instance
  • @param method the method to register
  • @param mapping the mapping conditions associated with the handler method
  • @throws IllegalStateException if another method was already registered
  • under the same mapping
    */

protected void registerHandlerMethod(Object handler, Method method, T mapping) {

    this.mappingRegistry.register(mapping, handler, method);

}
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register方法是AbstractHandlerMethodMapping 外部类MappingRegistry里的方法，