springMVC源码分析--AbstractHandlerMethodMapping获取url和HandlerMethod对应关系（十）

在之前的博客springMVC源码分析--AbstractHandlerMapping（二）中我们介绍了AbstractHandlerMethodMapping的父类AbstractHandlerMapping，其定义了抽象方法getHandlerInternal(HttpServletRequest request)，我看一下其在AbstractHandlerMethodMapping中的实现。

在AbstractHandlerMethodMapping中getHandlerInternal的实现如下：

//根据request来获取HandlerMethod
	@Override
	protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
		//获取请求连接
		String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
		if (logger.isDebugEnabled()) {
			logger.debug("Looking up handler method for path " + lookupPath);
		}
		//读锁
		this.mappingRegistry.acquireReadLock();
		try {
			//获取HandlerMethod
			HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);
			if (logger.isDebugEnabled()) {
				if (handlerMethod != null) {
					logger.debug("Returning handler method [" + handlerMethod + "]");
				}
				else {
					logger.debug("Did not find handler method for [" + lookupPath + "]");
				}
			}
			return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);
		}
		finally {
			this.mappingRegistry.releaseReadLock();
		}
	}

具体的实现是在lookupHandlerMethod中，最终是在mappingRegistry中获取HandlerMethod，mappingRegistry可以看似是一个Map结构（其实其包含了3个map），包含了url和HandlerMethod的对应关系。

protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
		List<Match> matches = new ArrayList<Match>();
		//从mappingRegistry中获取directPathMatches匹配关系
		List<T> directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath);
		if (directPathMatches != null) {
			addMatchingMappings(directPathMatches, matches, request);
		}
		if (matches.isEmpty()) {
			// No choice but to go through all mappings...
			addMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request);
		}
		//最终返回HandlerMethod
		if (!matches.isEmpty()) {
			Comparator<Match> comparator = new MatchComparator(getMappingComparator(request));
			Collections.sort(matches, comparator);
			if (logger.isTraceEnabled()) {
				logger.trace("Found " + matches.size() + " matching mapping(s) for [" +
						lookupPath + "] : " + matches);
			}
			Match bestMatch = matches.get(0);
			if (matches.size() > 1) {
				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();
					throw new IllegalStateException("Ambiguous handler methods mapped for HTTP path '" +
							request.getRequestURL() + "': {" + m1 + ", " + m2 + "}");
				}
			}
			handleMatch(bestMatch.mapping, lookupPath, request);
			return bestMatch.handlerMethod;
		}
		else {
			return handleNoMatch(this.mappingRegistry.getMappings().keySet(), lookupPath, request);
		}
	}

以下几个方法是在查找url和HandlerMethod的过程中一些帮助实现。

private void addMatchingMappings(Collection<T> mappings, List<Match> matches, HttpServletRequest request) {
		for (T mapping : mappings) {
			T match = getMatchingMapping(mapping, request);
			if (match != null) {
				matches.add(new Match(match, this.mappingRegistry.getMappings().get(mapping)));
			}
		}
	}
	//在子类中实现
	protected abstract T getMatchingMapping(T mapping, HttpServletRequest request);

	protected abstract Comparator<T> getMappingComparator(HttpServletRequest request);

	protected void handleMatch(T mapping, String lookupPath, HttpServletRequest request) {
		request.setAttribute(HandlerMapping.PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE, lookupPath);
	}
	//在子类中实现
	protected HandlerMethod handleNoMatch(Set<T> mappings, String lookupPath, HttpServletRequest request)
			throws Exception {

		return null;
	}