Spring中HandlerMapping接口源码详解
目录
- 前言
- 1.HandlerMapping的初始化
- 2.RequestMappingHandlerMapping处理reques请求
前言
实现HandlerMapping接口的类用来定义request请求和handler object之间的映射关系;request请求可以理解为路由url、RequestMappingInfo,handler object理解为控制器类;
RequestMappingHandlerMapping类就是实现此接口并将容器中所有的控制器的RequestMappingInfo请求和HandlerMethod注册到内存之中,方便真实的请求发送过来调用具体的控制器方法;
本文将以RequestMappingHandlerMapping为主线来讲解。
接口源码如下:
public interface HandlerMapping { /** * 返回一个包含handler Object和所有拦截器的HandlerExecutionChain */ @Nullable HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception; }
1.HandlerMapping的初始化
容器加载时DispatcherServlet中的初始化方法initStrategies会被调用,里面的initHandlerMappings(context)方法会被执行,源码如下:
//容器中HandlerMapping接口实现类集合 @Nullable private List<HandlerMapping> handlerMappings; private void initHandlerMappings(ApplicationContext context) { this.handlerMappings = null; //判定是否检测所有的HandlerMapping if (this.detectAllHandlerMappings) { //查看容器中所有的实现了HandlerMapping的bean Map<String, HandlerMapping> matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false); if (!matchingBeans.isEmpty()) { this.handlerMappings = new ArrayList<>(matchingBeans.values()); // 使用实现类的order进行优先级排序,升序 AnnotationAwareOrderComparator.sort(this.handlerMappings); } } else { try { //加载缺省的HandlerMapping HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class); this.handlerMappings = Collections.singletonList(hm); } catch (NoSuchBeanDefinitionException ex) { // Ignore, we'll add a default HandlerMapping later. } } // Ensure we have at least one HandlerMapping, by registering // a default HandlerMapping if no other mappings are found. if (this.handlerMappings == null) { this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class); if (logger.isTraceEnabled()) { logger.trace("No HandlerMappings declared for servlet '" + getServletName() + "': using default strategies from DispatcherServlet.properties"); } } }
上面的源码是从容器中获取HandlerMapping接口的实现类,其中包括RequestMappingHandlerMapping类实例,那这个类实例实在哪里加载的呢?
2.RequestMappingHandlerMapping处理reques请求
前端发送过来一个request请求首先进入DispatcherServlet的DOService方法,再进入doDispatch方法
本文的重点是通过request请求如何获取HandlerExecutionChain处理程序执行器链;HandlerExecutionChain是一个很重要的类,所有的HandlerMethod最终都要包装成HandlerExecutionChain后才可以使用;
跳出正文主题分析下HandlerExecutionChain类:
Handler execution chain, consisting of handler object and any handler interceptors. Returned by HandlerMapping’s {@link HandlerMapping#getHandler} method.
上面官方说明已经说的很清楚了,该类包含handler object(HandlerMethod)和所有的handler interceptors;而且该类的生成只能通过HandlerMapping接口的getHandler方法,具体由AbstractHandlerMapping抽象类实现;AbstractHandlerMapping类实现源码:
/** * 根据request请求获取HandlerExecutionChain处理程序执行器链 * Look up a handler for the given request, falling back to the default * handler if no specific one is found. * @param request current HTTP request * @return the corresponding handler instance, or the default handler * @see #getHandlerInternal */ @Override @Nullable public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception { //获取Handler object即HandlerMethod对象 Object handler = getHandlerInternal(request); if (handler == null) { //如果没有找到匹配的HandlerMethod对象,那么就获取默认的handler handler = getDefaultHandler(); } if (handler == null) { return null; } // Bean name or resolved handler? if (handler instanceof String) { String handlerName = (String) handler; handler = obtainApplicationContext().getBean(handlerName); } //根据编程上面获取的handler object获取处理程序执行器链类HandlerExecutionChain HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request); if (logger.isTraceEnabled()) { logger.trace("Mapped to " + handler); } else if (logger.isDebugEnabled() && !request.getDispatcherType().equals(DispatcherType.ASYNC)) { logger.debug("Mapped to " + executionChain.getHandler()); } //有跨域相关配置时执行如下代码 if (hasCorsConfigurationSource(handler) || CorsUtils.isPreFlightRequest(request)) { CorsConfiguration config = (this.corsConfigurationSource != null ? this.corsConfigurationSource.getCorsConfiguration(request) : null); CorsConfiguration handlerConfig = getCorsConfiguration(handler, request); config = (config != null ? config.combine(handlerConfig) : handlerConfig); executionChain = getCorsHanhttp://www.devze.comdlerExecutionChain(request, executionChain, config); } return executionChain; }
看下getHandlerInternal方法如何获取HandlerMethod对象:
/** * 通过request请求获取对应的HandlerMethod类 */ @Override protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception { //获取请求URL String lookupPath = getUrlPathHelper().getLookupPathForRequest(request); request.setAttribute(LOOKUP_PATH, lookupPath); this.mappingRegistry.acquireReadLock(); try { //获取URL对应的HandlerMethod,重点是我们如何获取HandlerMethod对象? HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request); return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null); } finally { this.mappingRegistry.releaseReadLock(); } }
看lookupHandlerMethod源码:
/** * 通过URL获取HandlerMethod对象 */ @Nullable protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception { List<Match> matches = new ArrayList<>(); //通过URL获取RequestMappingInfo集合 List<T> directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath); if (directPathMatches != null) { //将RequestMappingInfo对象和HandlerMethod对象封装到Match对象中存到matches集合 addMatchingMappings(directPathMatches, matches, request); } if (matches.isEmpty()) { // No choice but to go 编程through all mappings... addMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request); } if (!matches.isEmpty()) { //获取集合中第一个Match对象 Match bestMatch = matches.get(0); if (matches.size() > 1) { 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 + "}"); } } request.setAttribute(BEST_MATCHING_HANDLER_ATTRIBUTE, bestMatch.handlerMethod); handleMatch(bestMatch.androidmapping, lookupPath, request); //返回HandlerMethod对象 return bestMatch.handlerMethod; } else { return handleNoMatch(this.mappingRegistry.getMappings().keySet(), lookupPath, request); } }
上面的代码有一个this.mappingRegistry.getMappingsByUrl(lookupPath)方法获取url对应的RequestMappingInfo对象,源码如下:
//URL和RequestMappingInfo集合 private final MultiValueMap<String, T> urlLookup = new LinkedMultiValueMap<>(); /** * 返回与URL匹配的RequestMappingInfo集合 */ @Nullable public List<T> getMappingsByUrl(String urlPath) { return this.urlLookup.get(urlPath); }
上面的源码显示RequestMappingInfo对象是从urlLookup集合中获取的,那urlLookup集合中的数据又是从哪里来的呢?请看我的另外一篇文章RequestMappingHandlerMapping源码分析。
上面代码有一个addMatchingMappings方法,是通过这个方法获取到的HandlerMethod对象,看下源码:
private void addMatchingMappings(Collection<T> mappings, List<Match> matches, HttpServletRequest request) { //循环遍历RequestMappingInfo对象 for (T mapping : mappings) { // T match = getMatchingMapping(mapping, request); if (match != null) { //通过this.mappingRegistry.getMappings()获取HandlerMethod对象 matches.add(new Match(match, this.mappingRegistry.getMappings().get(mapping))); } } } //RequestMappingInfo和HandlerMethod集合 private final Map<T, HandlerMethod> mappingLookup = new LinkedHashMap<>(); /** * Return all mappings and handler methods. Not thread-safe. * @see #acquireReadLock() */ public Map<T, HandlerMethod> getMappings() { return this.mappingLookup; }
上面源码获取HandlerMethod对象实际上是从mappingLookUp集合之中获取的,那你可能会问mappingLookup集合中的数据又是从哪里获取到的呢?请看我的另外一篇文章RequestMappingHandlerMapping源码分析;
回到正文,编程我们看下mappedHandler = getHandler(processedRequest);方法,源码如下:
/** * Return the HandlerExecutionChain for this request. * <p>Tries all handler mappings in order. * @param request current HTTP request * @return the HandlerExecutionChain, or {@code null} if no handler could be found */ @Nullable protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception { if (this.handlerMappings != null) { //循环HandlerMapping实现类集合,其中包括RequestMappingHandlerMapping for (HandlerMapping mapping : this.handlerMappings) { //调用HandlerMapping实现类的getHandler方法,并获取程序执行器链类对象 HandlerExecutionChain handler = mapping.getHandler(request); if (handler != null) { //如果匹配直接返回,否则返回null return handler; } } } return null; }
通过上面我们一步步的分析源码,知道了HandlerExecutionChain处理程序执行器链是如何获取的,HandlerExecutionChain里面包含了请求对应的HandlerMethod对象和所有有关的连接器;
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