DispatcherServlet 源码解析
概述
DispatcherServlet是springMVC的核心，其本质是一个Servlet，主要进行全局的流程控制。DispatcherServlet继承FrameworkServlet抽象类，FrameworkServlet抽象类继承HttpServletBean实现ApplicationContextAware接口。HttpServletBean继承HttpServlet。FrameworkServlet重写了service()、destory()方法，service()增加了PATCH类型请求受理。真正处理请求的是
DispatcherServlet的doService()方法下的doDispatch()
DispatcherServlet运行流程：客户端发送HTTP请求，到达dispatcherServelt，dispatcherServelt调用handlerMapping将会把请求映射为HandlerExecutionChain对象（包含一个Handler处理器,多个HandlerInterceptor拦截器)。
DispatcherServlet-->HandlerAdapter,HandlerAdapter将会把处理器包装为适配器，从而支持多种类型的处理器。
HandlerAdapter-->处理器功能处理方法的调用，HandlerAdapter将会根据适配的结果调用真正的处理器的功能处理方法，完成功能处理，并返回一个ModelAndView对象(包含模型数据，逻辑视图名)。
ModelAndView的逻辑视图名-->ViewResolver，ViewResoler将把逻辑视图名解析为具体的View。
View-->渲染，View会根据传进来的Model模型数据进行渲染，此处的Model实际是一个Map数据结构。
返回控制权给DispatcherServlet，由DispatcherServlet返回响应给用户。
service 方法
Servlet接口, 定义了 service()方法。HttpServlet实现了service()方法。FrameworkServlet抽象类重写了service()方法增加了PATCH类型请求。方法最终指向了 processRequest() 方法
processRequest 方法
protected final void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
long startTime = System.currentTimeMillis();
Throwable failureCause = null;
// 获取LocaleContextHolder中保存的原始LocaleContext
LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
// 创建当前请求的LocaleContext
LocaleContext localeContext = this.buildLocaleContext(request);
// 获取RequestContextHolder中保存的原始RequestAttributes
RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
// 创建当前请求的RequestAttributes
ServletRequestAttributes requestAttributes = this.buildRequestAttributes(request, response, previousAttributes);
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new FrameworkServlet.RequestBindingInterceptor());
//将localeContext、requestAttributes分别设置到LocaleContextHolder和RequestContextHolder
this.initContextHolders(request, localeContext, requestAttributes);
try {
// 模板方法，DispatcherServlet中实现
this.doService(request, response);
} catch (ServletException var17) {
failureCause = var17;
throw var17;
} catch (IOException var18) {
failureCause = var18;
throw var18;
} catch (Throwable var19) {
failureCause = var19;
throw new NestedServletException("Request processing failed", var19);
} finally {
this.resetContextHolders(request, previousLocaleContext, previousAttributes);
if (requestAttributes != null) {
requestAttributes.requestCompleted();
}
if (this.logger.isDebugEnabled()) {
if (failureCause != null) {
this.logger.debug("Could not complete request", (Throwable)failureCause);
} else if (asyncManager.isConcurrentHandlingStarted()) {
this.logger.debug("Leaving response open for concurrent processing");
} else {
this.logger.debug("Successfully completed request");
}
}
this.publishRequestHandledEvent(request, response, startTime, (Throwable)failureCause);
}
}
doService 方法
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
if (this.logger.isDebugEnabled()) {
String resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult() ? " resumed" : "";
this.logger.debug("DispatcherServlet with name '" + this.getServletName() + "'" + resumed + " processing " + request.getMethod() + " request for [" + getRequestUri(request) + "]");
}
Map<String, Object> attributesSnapshot = null;
if (WebUtils.isIncludeRequest(request)) {
attributesSnapshot = new HashMap();
Enumeration attrNames = request.getAttributeNames();
label108:
while(true) {
String attrName;
do {
if (!attrNames.hasMoreElements()) {
break label108;
}
attrName = (String)attrNames.nextElement();
} while(!this.cleanupAfterInclude && !attrName.startsWith("org.springframework.web.servlet"));
attributesSnapshot.put(attrName, request.getAttribute(attrName));
}
}
request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.getWebApplicationContext());
request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
request.setAttribute(THEME_SOURCE_ATTRIBUTE, this.getThemeSource());
FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
if (inputFlashMap != null) {
request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
}
request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);
try {
this.doDispatch(request, response);
} finally {
if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted() && attributesSnapshot != null) {
this.restoreAttributesAfterInclude(request, attributesSnapshot);
}
}
}
- 此方法给request设置一些值，主要方法在doDispatch(request,response);
doDispatch 核心方法
- 检查是否是文件上传类型
- 获取HandlerExecutionChain
- 适配器模式,包装处理getHandler
- 执行preHandle拦截器,判断是否通过
- 执行controller中的方法
- 设置视图
- 执行拦截器的postHandle方法
- 判断解析视图是否成功
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
try {
ModelAndView mv = null;
Object dispatchException = null;
try {
//检查是否文件类型请求
processedRequest = this.checkMultipart(request);
multipartRequestParsed = processedRequest != request;
//获取HandlerExecutionChain
mappedHandler = this.getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
this.noHandlerFound(processedRequest, response);
return;
}
//适配器模式,包装处理getHandler
HandlerAdapter ha = this.getHandlerAdapter(mappedHandler.getHandler());
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (this.logger.isDebugEnabled()) {
this.logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
}
if ((new ServletWebRequest(request, response)).checkNotModified(lastModified) && isGet) {
return;
}
}
//执行preHandle拦截器,判断是否通过
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
//执行controller中的方法
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
//设置视图
this.applyDefaultViewName(processedRequest, mv);
//执行拦截器的postHandle方法
mappedHandler.applyPostHandle(processedRequest, response, mv);
} catch (Exception var20) {
dispatchException = var20;
} catch (Throwable var21) {
dispatchException = new NestedServletException("Handler dispatch failed", var21);
}
//判断解析视图是否成功
this.processDispatchResult(processedRequest, response, mappedHandler, mv, (Exception)dispatchException);
} catch (Exception var22) {
this.triggerAfterCompletion(processedRequest, response, mappedHandler, var22);
} catch (Throwable var23) {
this.triggerAfterCompletion(processedRequest, response, mappedHandler, new NestedServletException("Handler processing failed", var23));
}
} finally {
if (asyncManager.isConcurrentHandlingStarted()) {
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
} else if (multipartRequestParsed) {
this.cleanupMultipart(processedRequest);
}
}
}