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springmvc源码浅析(基于spring3.1.0)
请求处理过程:通过url找到对应Controller类中处理请求的方法,执行方法返回结果视图的过程.大致分为三个步骤:
其一,ApplicationContext初始化时建立所有url和controller类的对应关系(用Map保存);
其二,根据请求url找到对应的controller,并从controller中找到处理请求的方法;
其三,执行方法处理请求,并返回结果视图.
我们首先看第一个步骤,也就是建立Map<url,controller>关系的部分.第一部分的入口类为ApplicationObjectSupport的setApplicationContext方法.setApplicationContext方法中核心部分就是初始化容器initApplicationContext(context),子类AbstractDetectingUrlHandlerMapping实现了该方法,所以我们直接看子类中的初始化容器方法.
public void initApplicationContext() throws ApplicationContextException { super.initApplicationContext(); detectHandlers(); } /**
* 建立当前ApplicationContext中的所有controller和url的对应关系
*/ protected void detectHandlers() throws BeansException { if (logger.isDebugEnabled()) { logger.debug("Looking for URL mappings in application context: " + getApplicationContext()); }
// 获取ApplicationContext容器中所有bean的Name String[] beanNames = (this.detectHandlersInAncestorContexts ? BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(), Object.class) : getApplicationContext().getBeanNamesForType(Object.class)); // 遍历beanNames,并找到这些bean对应的url for (String beanName : beanNames) {
// 找bean上的所有url(controller上的url+方法上的url),该方法由对应的子类实现 String[] urls = determineUrlsForHandler(beanName); if (!ObjectUtils.isEmpty(urls)) { // 保存urls和beanName的对应关系,put it to Map<urls,beanName>,该方法在父类AbstractUrlHandlerMapping中实现 registerHandler(urls, beanName); } else { if (logger.isDebugEnabled()) { logger.debug("Rejected bean name ‘" + beanName + "‘: no URL paths identified"); } } } }
protected abstract String[] determineUrlsForHandler(String beanName);
DefaultAnnotationHandlerMapping是AbstractDetectingUrlHandlerMapping的子类,处理注解形式的url映射.因为实际开发中,通过注解来配置url是我们最常用的方式,所以我们这里以DefaultAnnotationHandlerMapping来进行分析.我们看DefaultAnnotationHandlerMapping是如何查找beanName上所有映射的url.
/**
* 获取controller中所有的url
*/
protected String[] determineUrlsForHandler(String beanName) { // 获取ApplicationContext容器
ApplicationContext context = getApplicationContext(); //从容器中获取controller
Class<?> handlerType = context.getType(beanName);
// 获取controller上的@RequestMapping注解 RequestMapping mapping = context.findAnnotationOnBean(beanName, RequestMapping.class); if (mapping != null) { // controller上有注解 this.cachedMappings.put(handlerType, mapping);
// 返回结果集 Set<String> urls = new LinkedHashSet<String>();
// controller的映射url String[] typeLevelPatterns = mapping.value(); if (typeLevelPatterns.length > 0) { // url>0 // 获取controller中所有方法及方法的映射url String[] methodLevelPatterns = determineUrlsForHandlerMethods(handlerType, true); for (String typeLevelPattern : typeLevelPatterns) { if (!typeLevelPattern.startsWith("/")) { typeLevelPattern = "/" + typeLevelPattern; } boolean hasEmptyMethodLevelMappings = false; for (String methodLevelPattern : methodLevelPatterns) { if (methodLevelPattern == null) { hasEmptyMethodLevelMappings = true; } else {
// controller的映射url+方法映射的url String combinedPattern = getPathMatcher().combine(typeLevelPattern, methodLevelPattern);
// 保存到set集合中
addUrlsForPath(urls, combinedPattern); } } if (hasEmptyMethodLevelMappings || org.springframework.web.servlet.mvc.Controller.class.isAssignableFrom(handlerType)) { addUrlsForPath(urls, typeLevelPattern); } }
// 以数组形式返回controller上的所有url return StringUtils.toStringArray(urls); } else { // controller上的@RequestMapping映射url为空串,直接找方法的映射url return determineUrlsForHandlerMethods(handlerType, false); } } // controller上没@RequestMapping注解 else if (AnnotationUtils.findAnnotation(handlerType, Controller.class) != null) { // 获取controller中方法上的映射url return determineUrlsForHandlerMethods(handlerType, false); } else { return null; } }
到这里,第一个步骤就完成了!下面我们开始分析第二个步骤,第二个步骤是由请求触发的,所以入口为DispatcherServlet.DispatcherServlet的核心方法为doService(),doService()中的核心逻辑由doDispatch()实现,我们查看doDispatch()的源代码.
/** 中央控制器,控制请求的转发 **/
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { HttpServletRequest processedRequest = request; HandlerExecutionChain mappedHandler = null; int interceptorIndex = -1; try { ModelAndView mv; boolean errorView = false; try {
// 1.检查是否是文件上传的请求 processedRequest = checkMultipart(request); // 2.取得处理当前请求的controller,这里也称为hanlder,处理器,第一个步骤的意义就在这里体现了.这里并不是直接返回controller,而是返回的HandlerExecutionChain请求处理器链对象,该对象封装了handler和interceptors. mappedHandler = getHandler(processedRequest, false);
// 如果handler为空,则返回404 if (mappedHandler == null || mappedHandler.getHandler() == null) { noHandlerFound(processedRequest, response); return; } //3. 获取处理request的处理器适配器handler adapter HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler()); // 处理 last-modified 请求头 String method = request.getMethod(); boolean isGet = "GET".equals(method); if (isGet || "HEAD".equals(method)) { long lastModified = ha.getLastModified(request, mappedHandler.getHandler()); if (logger.isDebugEnabled()) { String requestUri = urlPathHelper.getRequestUri(request); logger.debug("Last-Modified value for [" + requestUri + "] is: " + lastModified); } if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) { return; } } // 4.拦截器的预处理方法 HandlerInterceptor[] interceptors = mappedHandler.getInterceptors(); if (interceptors != null) { for (int i = 0; i < interceptors.length; i++) { HandlerInterceptor interceptor = interceptors[i]; if (!interceptor.preHandle(processedRequest, response, mappedHandler.getHandler())) { triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null); return; } interceptorIndex = i; } } // 5.实际的处理器处理请求,返回结果视图对象 mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); // 结果视图对象的处理 if (mv != null && !mv.hasView()) { mv.setViewName(getDefaultViewName(request)); } // 6.拦截器的后处理方法 if (interceptors != null) { for (int i = interceptors.length - 1; i >= 0; i--) { HandlerInterceptor interceptor = interceptors[i]; interceptor.postHandle(processedRequest, response, mappedHandler.getHandler(), mv); } } } catch (ModelAndViewDefiningException ex) { logger.debug("ModelAndViewDefiningException encountered", ex); mv = ex.getModelAndView(); } catch (Exception ex) { Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null); mv = processHandlerException(processedRequest, response, handler, ex); errorView = (mv != null); } if (mv != null && !mv.wasCleared()) { render(mv, processedRequest, response); if (errorView) { WebUtils.clearErrorRequestAttributes(request); } } else { if (logger.isDebugEnabled()) { logger.debug("Null ModelAndView returned to DispatcherServlet with name ‘" + getServletName() + "‘: assuming HandlerAdapter completed request handling"); } } // 请求成功响应之后的方法 triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null); }
上面的方法中,第2步其实就是从第一个步骤中的Map<urls,beanName>中取得controller,然后经过拦截器的预处理方法,到最核心的部分--第5步调用controller的方法处理请求.在第2步中我们可以知道处理request的controller,第5步就是要根据url确定controller中处理请求的方法,然后通过反射获取该方法上的注解和参数,解析方法和参数上的注解,最后反射调用方法获取ModelAndView结果视图。因为上面采用注解url形式说明的,所以我们这里继续以注解处理器适配器来说明.第5步调用的就是AnnotationMethodHandlerAdapter的handle().handle()中的核心逻辑由invokeHandlerMethod(request, response, handler)实现,直接看他的代码:
/** 获取处理请求的方法,执行并返回结果视图 **/
protected ModelAndView invokeHandlerMethod(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { // 1.获取方法解析器 ServletHandlerMethodResolver methodResolver = getMethodResolver(handler);
// 2.解析request中的url,获取处理request的方法 Method handlerMethod = methodResolver.resolveHandlerMethod(request);
// 3.方法调用器 ServletHandlerMethodInvoker methodInvoker = new ServletHandlerMethodInvoker(methodResolver); ServletWebRequest webRequest = new ServletWebRequest(request, response); ExtendedModelMap implicitModel = new BindingAwareModelMap(); // 4.执行方法 Object result = methodInvoker.invokeHandlerMethod(handlerMethod, handler, webRequest, implicitModel);
// 5.封装结果视图 ModelAndView mav = methodInvoker.getModelAndView(handlerMethod, handler.getClass(), result, implicitModel, webRequest); methodInvoker.updateModelAttributes(handler, (mav != null ? mav.getModel() : null), implicitModel, webRequest); return mav; }
这一部分的核心就在2和4了.先看第2步,通过request找controller的处理方法.
、** 根据url获取处理请求的方法 **/
public Method resolveHandlerMethod(HttpServletRequest request) throws ServletException {
// 如果请求url为,localhost:8080/springmvc/helloWorldController/say.action, 则lookupPath=helloWorldController/say.action String lookupPath = urlPathHelper.getLookupPathForRequest(request); Comparator<String> pathComparator = pathMatcher.getPatternComparator(lookupPath); Map<RequestSpecificMappingInfo, Method> targetHandlerMethods = new LinkedHashMap<RequestSpecificMappingInfo, Method>(); Set<String> allowedMethods = new LinkedHashSet<String>(7); String resolvedMethodName = null;
// 遍历controller上的所有方法,获取url匹配的方法 for (Method handlerMethod : getHandlerMethods()) { RequestSpecificMappingInfo mappingInfo = new RequestSpecificMappingInfo(this.mappings.get(handlerMethod)); boolean match = false; if (mappingInfo.hasPatterns()) {// 获取方法上的url for (String pattern : mappingInfo.getPatterns()) { // 方法上可能有多个url,springmvc支持方法映射多个url if (!hasTypeLevelMapping() && !pattern.startsWith("/")) { pattern = "/" + pattern; }
// 获取controller上的映射和url和方法上的url,拼凑起来与lookupPath是否匹配 String combinedPattern = getCombinedPattern(pattern, lookupPath, request); if (combinedPattern != null) { if (mappingInfo.matches(request)) { match = true; mappingInfo.addMatchedPattern(combinedPattern); } else { if (!mappingInfo.matchesRequestMethod(request)) { allowedMethods.addAll(mappingInfo.methodNames()); } break; } } } mappingInfo.sortMatchedPatterns(pathComparator); } else if (useTypeLevelMapping(request)) { // other }
通过上面的代码,已经可以找到处理request的controller中的方法了,现在看如何解析该方法上的参数,并调用该方法。也就是执行方法这一步.执行方法这一步最重要的就是获取方法的参数,然后我们就可以反射调用方法了.
public final Object invokeHandlerMethod(Method handlerMethod, Object handler, NativeWebRequest webRequest, ExtendedModelMap implicitModel) throws Exception {
Method handlerMethodToInvoke = BridgeMethodResolver.findBridgedMethod(handlerMethod); try { boolean debug = logger.isDebugEnabled();
// 处理方法上的其他注解 for (String attrName : this.methodResolver.getActualSessionAttributeNames()) { Object attrValue = this.sessionAttributeStore.retrieveAttribute(webRequest, attrName); if (attrValue != null) { implicitModel.addAttribute(attrName, attrValue); } } for (Method attributeMethod : this.methodResolver.getModelAttributeMethods()) { Method attributeMethodToInvoke = BridgeMethodResolver.findBridgedMethod(attributeMethod); Object[] args = resolveHandlerArguments(attributeMethodToInvoke, handler, webRequest, implicitModel); if (debug) { logger.debug("Invoking model attribute method: " + attributeMethodToInvoke); } String attrName = AnnotationUtils.findAnnotation(attributeMethod, ModelAttribute.class).value(); if (!"".equals(attrName) && implicitModel.containsAttribute(attrName)) { continue; } ReflectionUtils.makeAccessible(attributeMethodToInvoke); Object attrValue = attributeMethodToInvoke.invoke(handler, args); if ("".equals(attrName)) { Class resolvedType = GenericTypeResolver.resolveReturnType(attributeMethodToInvoke, handler.getClass()); attrName = Conventions.getVariableNameForReturnType(attributeMethodToInvoke, resolvedType, attrValue); } if (!implicitModel.containsAttribute(attrName)) { implicitModel.addAttribute(attrName, attrValue); } }
// 核心代码,获取方法上的参数值 Object[] args = resolveHandlerArguments(handlerMethodToInvoke, handler, webRequest, implicitModel); if (debug) { logger.debug("Invoking request handler method: " + handlerMethodToInvoke); } ReflectionUtils.makeAccessible(handlerMethodToInvoke); return handlerMethodToInvoke.invoke(handler, args); }
resolveHandlerArguments方法实现代码很多,目的就是获取方法参数列表对应参数的值.把握这个思路就不会被这么长的代码吓到.
private Object[] resolveHandlerArguments(Method handlerMethod, Object handler, NativeWebRequest webRequest, ExtendedModelMap implicitModel) throws Exception { // 1.获取方法参数类型的数组 Class[] paramTypes = handlerMethod.getParameterTypes();
// 声明数组,存参数的值 Object[] args = new Object[paramTypes.length]; //2.遍历参数数组,获取每个参数的值 for (int i = 0; i < args.length; i++) { MethodParameter methodParam = new MethodParameter(handlerMethod, i); methodParam.initParameterNameDiscovery(this.parameterNameDiscoverer); GenericTypeResolver.resolveParameterType(methodParam, handler.getClass()); String paramName = null; String headerName = null; boolean requestBodyFound = false; String cookieName = null; String pathVarName = null; String attrName = null; boolean required = false; String defaultValue = null; boolean validate = false; int annotationsFound = 0; Annotation[] paramAnns = methodParam.getParameterAnnotations(); // 处理参数上的注解 for (Annotation paramAnn : paramAnns) { if (RequestParam.class.isInstance(paramAnn)) { RequestParam requestParam = (RequestParam) paramAnn; paramName = requestParam.value(); required = requestParam.required(); defaultValue = parseDefaultValueAttribute(requestParam.defaultValue()); annotationsFound++; } else if (RequestHeader.class.isInstance(paramAnn)) { RequestHeader requestHeader = (RequestHeader) paramAnn; headerName = requestHeader.value(); required = requestHeader.required(); defaultValue = parseDefaultValueAttribute(requestHeader.defaultValue()); annotationsFound++; } else if (RequestBody.class.isInstance(paramAnn)) { requestBodyFound = true; annotationsFound++; } else if (CookieValue.class.isInstance(paramAnn)) { CookieValue cookieValue = (CookieValue) paramAnn; cookieName = cookieValue.value(); required = cookieValue.required(); defaultValue = parseDefaultValueAttribute(cookieValue.defaultValue()); annotationsFound++; } else if (PathVariable.class.isInstance(paramAnn)) { PathVariable pathVar = (PathVariable) paramAnn; pathVarName = pathVar.value(); annotationsFound++; } else if (ModelAttribute.class.isInstance(paramAnn)) { ModelAttribute attr = (ModelAttribute) paramAnn; attrName = attr.value(); annotationsFound++; } else if (Value.class.isInstance(paramAnn)) { defaultValue = ((Value) paramAnn).value(); } else if ("Valid".equals(paramAnn.annotationType().getSimpleName())) { validate = true; } } if (annotationsFound > 1) { throw new IllegalStateException("Handler parameter annotations are exclusive choices - " + "do not specify more than one such annotation on the same parameter: " + handlerMethod); } if (annotationsFound == 0) { Object argValue = resolveCommonArgument(methodParam, webRequest); if (argValue != WebArgumentResolver.UNRESOLVED) { args[i] = argValue; } else if (defaultValue != null) { args[i] = resolveDefaultValue(defaultValue); } else { Class paramType = methodParam.getParameterType(); if (Model.class.isAssignableFrom(paramType) || Map.class.isAssignableFrom(paramType)) { args[i] = implicitModel; } else if (SessionStatus.class.isAssignableFrom(paramType)) { args[i] = this.sessionStatus; } else if (HttpEntity.class.isAssignableFrom(paramType)) { args[i] = resolveHttpEntityRequest(methodParam, webRequest); } else if (Errors.class.isAssignableFrom(paramType)) { throw new IllegalStateException("Errors/BindingResult argument declared " + "without preceding model attribute. Check your handler method signature!"); } else if (BeanUtils.isSimpleProperty(paramType)) { paramName = ""; } else { attrName = ""; } } } // 从request中取值,并进行赋值操作 if (paramName != null) { args[i] = resolveRequestParam(paramName, required, defaultValue, methodParam, webRequest, handler); } else if (headerName != null) { args[i] = resolveRequestHeader(headerName, required, defaultValue, methodParam, webRequest, handler); } else if (requestBodyFound) { args[i] = resolveRequestBody(methodParam, webRequest, handler); } else if (cookieName != null) { args[i] = resolveCookieValue(cookieName, required, defaultValue, methodParam, webRequest, handler); } else if (pathVarName != null) { args[i] = resolvePathVariable(pathVarName, methodParam, webRequest, handler); } else if (attrName != null) { WebDataBinder binder = resolveModelAttribute(attrName, methodParam, implicitModel, webRequest, handler); boolean assignBindingResult = (args.length > i + 1 && Errors.class.isAssignableFrom(paramTypes[i + 1])); if (binder.getTarget() != null) { doBind(binder, webRequest, validate, !assignBindingResult); } args[i] = binder.getTarget(); if (assignBindingResult) { args[i + 1] = binder.getBindingResult(); i++; } implicitModel.putAll(binder.getBindingResult().getModel()); } } // 返回参数值数组 return args; }
到这里,核心代码就分析完了!剩下的结果视图处理就不说了!其实只要清楚了请求处理流程,看代码是比较清晰的!
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