SpringMVC源码解读 - HandlerMapping - AbstractUrlHandlerMapping系列request分发

AbstractHandlerMapping实现HandlerMapping接口定的getHandler

　　1. 提供getHandlerInternal模板方法给子类实现

　　2. 如果没有获取Handler,则使用默认的defaultHandler

　　3. 如果handler是string类型,从context获取实例

　　4. 通过getHandlerExecutionChain封装handler,添加interceptor

// AbstractHandlerMapping

     /**
      * 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
      */
     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) {
             String handlerName = (String) handler;
             handler = getApplicationContext().getBean(handlerName);
         }
         return getHandlerExecutionChain(handler, request);
     }

// AbstractHandlerMapping

     /**
      * Build a HandlerExecutionChain for the given handler, including applicable interceptors.
      * <p>The default implementation simply builds a standard HandlerExecutionChain with
      * the given handler, the handler mapping's common interceptors, and any {@link MappedInterceptor}s
      * matching to the current request URL. Subclasses may
      * override this in order to extend/rearrange the list of interceptors.
      * <p><b>NOTE:</b> The passed-in handler object may be a raw handler or a pre-built
      * HandlerExecutionChain. This method should handle those two cases explicitly,
      * either building a new HandlerExecutionChain or extending the existing chain.
      * <p>For simply adding an interceptor, consider calling {@code super.getHandlerExecutionChain}
      * and invoking {@link HandlerExecutionChain#addInterceptor} on the returned chain object.
      * @param handler the resolved handler instance (never {@code null})
      * @param request current HTTP request
      * @return the HandlerExecutionChain (never {@code null})
      * @see #getAdaptedInterceptors()
      */
     protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
         HandlerExecutionChain chain =
             (handler instanceof HandlerExecutionChain) ?
                 (HandlerExecutionChain) handler : new HandlerExecutionChain(handler);

         chain.addInterceptors(getAdaptedInterceptors());

         String lookupPath = urlPathHelper.getLookupPathForRequest(request);
         for (MappedInterceptor mappedInterceptor : mappedInterceptors) {
             if (mappedInterceptor.matches(lookupPath, pathMatcher)) {
                 chain.addInterceptor(mappedInterceptor.getInterceptor());
             }
         }

         return chain;
     }

接下来看看AbstractUrlHandlerMapping实现的getHandlerInternal

// AbstractUrlHandlerMapping

     /**
      * Look up a handler for the URL path of the given request.
      * @param request current HTTP request
      * @return the handler instance, or {@code null} if none found
      */
     @Override
     protected Object getHandlerInternal(HttpServletRequest request) throws Exception {
         // 根据request获取url
         String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
         // 根据url查找handler
         Object handler = lookupHandler(lookupPath, request);
         if (handler == null) {
             // 如果没有匹配到handler需要查找默认的,下面需要将PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE缓存到request
             // We need to care for the default handler directly, since we need to
             // expose the PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE for it as well.
             Object rawHandler = null;
             if ("/".equals(lookupPath)) {
                 rawHandler = getRootHandler();
             }
             if (rawHandler == null) {
                 rawHandler = getDefaultHandler();
             }
             if (rawHandler != null) {
                 // Bean name or resolved handler?
                 if (rawHandler instanceof String) {
                     String handlerName = (String) rawHandler;
                     rawHandler = getApplicationContext().getBean(handlerName);
                 }
                 // 预留的校验handler模板方法,没有使用
                 validateHandler(rawHandler, request);
                 // 添加expose属性到request的拦截器
                 handler = buildPathExposingHandler(rawHandler, lookupPath, lookupPath, null);
             }
         }
         if (handler != null && logger.isDebugEnabled()) {
             logger.debug("Mapping [" + lookupPath + "] to " + handler);
         }
         else if (handler == null && logger.isTraceEnabled()) {
             logger.trace("No handler mapping found for [" + lookupPath + "]");
         }
         return handler;
     }

// AbstractUrlHandlerMapping

     /**
      * Look up a handler instance for the given URL path.
      * <p>Supports direct matches, e.g. a registered "/test" matches "/test",
      * and various Ant-style pattern matches, e.g. a registered "/t*" matches
      * both "/test" and "/team". For details, see the AntPathMatcher class.
      * <p>Looks for the most exact pattern, where most exact is defined as
      * the longest path pattern.
      * @param urlPath URL the bean is mapped to
      * @param request current HTTP request (to expose the path within the mapping to)
      * @return the associated handler instance, or {@code null} if not found
      * @see #exposePathWithinMapping
      * @see org.springframework.util.AntPathMatcher
      */
     protected Object lookupHandler(String urlPath, HttpServletRequest request) throws Exception {
         // Direct match? 直接根据url进行查找handler
         Object handler = this.handlerMap.get(urlPath);
         if (handler != null) {
             // Bean name or resolved handler?
             if (handler instanceof String) {
                 String handlerName = (String) handler;
                 handler = getApplicationContext().getBean(handlerName);
             }
             validateHandler(handler, request);
             return buildPathExposingHandler(handler, urlPath, urlPath, null);
         }
         // Pattern match? 通过表达式进行匹配具体通过AntPathMatcher实现,具体后面分析
         List<String> matchingPatterns = new ArrayList<String>();
         for (String registeredPattern : this.handlerMap.keySet()) {
             if (getPathMatcher().match(registeredPattern, urlPath)) {
                 matchingPatterns.add(registeredPattern);
             }
         }
         String bestPatternMatch = null;
         Comparator<String> patternComparator = getPathMatcher().getPatternComparator(urlPath);
         if (!matchingPatterns.isEmpty()) {
             Collections.sort(matchingPatterns, patternComparator);
             if (logger.isDebugEnabled()) {
                 logger.debug("Matching patterns for request [" + urlPath + "] are " + matchingPatterns);
             }
             // order序号最小的优先级最高
             bestPatternMatch = matchingPatterns.get(0);
         }
         if (bestPatternMatch != null) {
             handler = this.handlerMap.get(bestPatternMatch);
             // Bean name or resolved handler?
             if (handler instanceof String) {
                 String handlerName = (String) handler;
                 handler = getApplicationContext().getBean(handlerName);
             }
             validateHandler(handler, request);
             String pathWithinMapping = getPathMatcher().extractPathWithinPattern(bestPatternMatch, urlPath);

             // There might be multiple 'best patterns', let's make sure we have the correct URI template variables
             // for all of them
             Map<String, String> uriTemplateVariables = new LinkedHashMap<String, String>();
             for (String matchingPattern : matchingPatterns) {
                 if (patternComparator.compare(bestPatternMatch, matchingPattern) == 0) {
                     Map<String, String> vars = getPathMatcher().extractUriTemplateVariables(matchingPattern, urlPath);
                     Map<String, String> decodedVars = getUrlPathHelper().decodePathVariables(request, vars);
                     uriTemplateVariables.putAll(decodedVars);
                 }
             }
             if (logger.isDebugEnabled()) {
                 logger.debug("URI Template variables for request [" + urlPath + "] are " + uriTemplateVariables);
             }
             return buildPathExposingHandler(handler, bestPatternMatch, pathWithinMapping, uriTemplateVariables);
         }
         // No handler found...
         return null;
     }

设计用于校验Handler,实际什么都没做,包括子类.

     /**
      * Validate the given handler against the current request.
      * <p>The default implementation is empty. Can be overridden in subclasses,
      * for example to enforce specific preconditions expressed in URL mappings.
      * @param handler the handler object to validate
      * @param request current HTTP request
      * @throws Exception if validation failed
      */
     protected void validateHandler(Object handler, HttpServletRequest request) throws Exception {
     }

封装handler为HandlerExecutionChain,并添加PathExposingHandlerInterceptor和UriTemplateVariablesHandlerInterceptor拦截器.

     /**
      * Build a handler object for the given raw handler, exposing the actual
      * handler, the {@link #PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE}, as well as
      * the {@link #URI_TEMPLATE_VARIABLES_ATTRIBUTE} before executing the handler.
      * <p>The default implementation builds a {@link HandlerExecutionChain}
      * with a special interceptor that exposes the path attribute and uri template variables
      * @param rawHandler the raw handler to expose
      * @param pathWithinMapping the path to expose before executing the handler
      * @param uriTemplateVariables the URI template variables, can be {@code null} if no variables found
      * @return the final handler object
      */
     protected Object buildPathExposingHandler(Object rawHandler, String bestMatchingPattern,
             String pathWithinMapping, Map<String, String> uriTemplateVariables) {

         HandlerExecutionChain chain = new HandlerExecutionChain(rawHandler);
         chain.addInterceptor(new PathExposingHandlerInterceptor(bestMatchingPattern, pathWithinMapping));
         if (!CollectionUtils.isEmpty(uriTemplateVariables)) {
             chain.addInterceptor(new UriTemplateVariablesHandlerInterceptor(uriTemplateVariables));
         }
         return chain;
     }