spring MVC源码探索之AbstractHandlerMethodMapping

• 为什么看源码？
• AbstractHandlerMethodMapping
• • initHandlerMethods()
  • isHandler()
  • detectHandlerMethods()
  • registerHandlerMethod()

为什么看源码？

这篇文章是第一个原因Spring MVC controller路径是否能重复？
第二个就是工作这么多年虽然看过一点框架源码，但是没有系统的看过，写上篇文章的时候看了源码，感觉还挺有意思就记录一下。
第三个就是一直都是在用也该了解一下原理了，至于框架的设计思路、大牛的想法什么的希望能在看源码的过程中学习到。

AbstractHandlerMethodMapping

官方解释是这样的。

/**
 * 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 

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维护着其唯一的一个映射，就是维护handler method 和URL的关系。主要用于@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，那我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.
	 */
	@Override
	public void afterPropertiesSet() {
		initHandlerMethods();
	}

在项目启动时会执行initHandlerMethods方法，它的主要功能是扫描应用上下文，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());
	}

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));
	}

isHandler()方法在这里的作用就是检查beanType是否有@Controller或@RequestMapping注解，这两个注解经常使用，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);
			});
		}
	}

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);
	}

register方法是AbstractHandlerMethodMapping 内部类MappingRegistry里的方法，MappingRegistry是一个注册表，对MappingRegistry有兴趣的可以看一下源码或者看一下我之前的一篇文章 Spring MVC controller路径是否能重复？

我这里只是很简单的记录一下我看的源码，也不全面最好自己能看一下源码。

水平有限，能力一般，如有错误，请多指出