SpringMVC源码解读之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. * 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. * NOTE: 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. * 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. * 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. * 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(); } 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) == ) { 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. * 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. * 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; }

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