Spring Boot 2.2.6 源码之旅二十二SpringMVC源码之DispatcherServlet的getHandler一

基本流程图，方法查看

DispatcherServlet的doDispatch的核心方法分析

getHandler获取处理器

看起来好像就没多少，其实内部东西还是挺多的，这里就是我们前面初始化的处理器映射器的作用，找到处理器，然后加入拦截器，封装成执行链HandlerExecutionChain 。遍历所有的处理器映射器，找到合适的就返回了。接下去我们看看他们是怎么找的，主要分析RequestMappingHandlerMapping和BeanNameUrlHandlerMapping，其他的有兴趣自己可以看，常用的是RequestMappingHandlerMapping。

	@Nullable
	protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
		if (this.handlerMappings != null) {
			for (HandlerMapping mapping : this.handlerMappings) {
				HandlerExecutionChain handler = mapping.getHandler(request);
				if (handler != null) {
					return handler;
				}
			}
		}
		return null;
	}

RequestMappingHandlerMapping的getHandler

我们研究一般的流程，不考虑CORS，其实就是尝试获取处理器，这里的处理器其实是封装的方法HandlerMethod，然后进行拦截器的封装。

	@Override
	@Nullable
	public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
		Object handler = getHandlerInternal(request);
		if (handler == null) {
			handler = getDefaultHandler();
		}
		if (handler == null) {
			return null;
		}
		// Bean name or resolved handler?
		if (handler instanceof String) {//如果没有实例化就实例化
			String handlerName = (String) handler;
			handler = obtainApplicationContext().getBean(handlerName);
		}
		//获取执行链
		HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);

		...


		return executionChain;
	}

AbstractHandlerMethodMapping的getHandlerInternal

核心方法是lookupHandlerMethod。

	@Override
	protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
		String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);//获取查找路径
		request.setAttribute(LOOKUP_PATH, lookupPath);
		this.mappingRegistry.acquireReadLock();
		try {
			HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);//查找方法
			return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);
		}
		finally {
			this.mappingRegistry.releaseReadLock();
		}
	}

AbstractHandlerMethodMapping的lookupHandlerMethod

首先去uri映射注册器里找是否有这个方法的集合，有的话直接处理，没有的话就遍历所有的uri处理，找出最匹配的HandlerMethod 返回。

@Nullable
	protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
		List<Match> matches = new ArrayList<>();
		List<T> directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath);
		if (directPathMatches != null) {//有path匹配的直接处理
			addMatchingMappings(directPathMatches, matches, request);
		}
		if (matches.isEmpty()) {//没有就遍历所有的处理
			// No choice but to go through all mappings...
			addMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request);
		}

		if (!matches.isEmpty()) {//有匹配的
			Match bestMatch = matches.get(0);
			if (matches.size() > 1) {//多个匹配的情况
				Comparator<Match> comparator = new MatchComparator(getMappingComparator(request));
				matches.sort(comparator);
				bestMatch = matches.get(0);
				if (logger.isTraceEnabled()) {
					logger.trace(matches.size() + " matching mappings: " + matches);
				}
				if (CorsUtils.isPreFlightRequest(request)) {
					return PREFLIGHT_AMBIGUOUS_MATCH;
				}
				Match secondBestMatch = matches.get(1);
				if (comparator.compare(bestMatch, secondBestMatch) == 0) {
					Method m1 = bestMatch.handlerMethod.getMethod();
					Method m2 = secondBestMatch.handlerMethod.getMethod();
					String uri = request.getRequestURI();
					throw new IllegalStateException(
							"Ambiguous handler methods mapped for '" + uri + "': {" + m1 + ", " + m2 + "}");
				}
			}//handlerMethod设置到属性里
			request.setAttribute(BEST_MATCHING_HANDLER_ATTRIBUTE, bestMatch.handlerMethod);
			handleMatch(bestMatch.mapping, lookupPath, request);
			return bestMatch.handlerMethod;
		}
		else {
			return handleNoMatch(this.mappingRegistry.getMappings().keySet(), lookupPath, request);
		}
	}

MappingRegistry的getMappingsByUrl

这个会先进行uri匹配，如果获取到了就直接返回，那这些uri是怎么来的，我们还是要先弄明白。

下篇介绍下这个uri怎么来的。

好了，今天就到这里了，希望对学习理解有帮助，大神看见勿喷，仅为自己的学习理解，能力有限，请多包涵。