我是靠谱客的博主 平常大侠，最近开发中收集的这篇文章主要介绍springMVC系列源码之请求处理过程——12springMVC系列源码之请求处理过程——12，觉得挺不错的，现在分享给大家，希望可以做个参考。
概述
springMVC系列源码之请求处理过程——12
摘要：上次主要分析springMVC启动时是如何加载配置文件以及做好初始化工作的、这里主要是分析请求处理过程、包括浏览器发送一个请求到服务器、服务器内部如何处理、又如何将处理结果返回、服务器做出响应的一个过程。
1、简介
当springMVC的初始化完成之后、就进入到Servlet的第二个阶段“Service“时期、当浏览器发送一个request的到服务器的时候、Servlet容器启动一个线程、通过service()方法将请求转到doGet或者doPost来处理。
此时springMVC已经建立了一个子上下文、此上下文中存放着通过依赖注入的各种编程元素。Struts2采取的是一种完全和Web容器隔离和解耦的事件机制。诸如Action对象、Result对象、Interceptor对象，这些都是完全脱离Servlet容器的编程元素。Struts2将数据流和事件处理完全剥离开来，从Http请求中读取数据后，下面的事件处理流程就只依赖于这些数据，而完全不知道有Web环境的存在。
反观SpringMVC，无论HandlerMapping对象、HandlerAdapter对象还是View对象，这些核心的接口所定义的方法中，HttpServletRequest和HttpServletResponse对象都是直接作为方法的参数出现的。这也就意味着，框架的设计者，直接将SpringMVC框架和容器绑定到了一起。或者说，整个SpringMVC框架，都是依托着Servlet容器元素来设计的。
DispatcherServlet作为一个标准的Servlet、那么当一个请求过来时、我们就可以按照Servlet的执行过程去分析、他是如何处理request的。对于springMVC的模版化设计模式、我们时常要去父类中寻找我们需要的方法。下面就从DispatcherServlet入手、来分析一个request的请求过程。
2、具体过程
2.1 浏览器发送一个请求（这里以一次GET方式的请求为例、POST一样！）。
2.2 请求到达服务器、进入DispatcherServlet中的doGet或者doPost中处理。
protected final void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
/**
* Delegate POST requests to {@link #processRequest}.
* @see #doService
*/
@Override
protected final void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}上面代码中都没有对request进行具体的处理、都是转由processRequest(request, response)处理。代码：
protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
Throwable failureCause = null;
LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
LocaleContext localeContext = buildLocaleContext(request);
RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
ServletRequestAttributes requestAttributes = null;
if (previousAttributes == null || (previousAttributes instanceof ServletRequestAttributes)) {
requestAttributes = new ServletRequestAttributes(request);
}
initContextHolders(request, localeContext, requestAttributes);
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), getRequestBindingInterceptor(request));
doService(request, response);
resetContextHolders(request, previousLocaleContext, previousAttributes);
if (requestAttributes != null) {
requestAttributes.requestCompleted();
}
if (this.publishEvents) {
// Whether or not we succeeded, publish an event.
long processingTime = System.currentTimeMillis() - startTime;
this.webApplicationContext.publishEvent(
new ServletRequestHandledEvent(this,
request.getRequestURI(), request.getRemoteAddr(),
request.getMethod(), getServletConfig().getServletName(),
WebUtils.getSessionId(request), getUsernameForRequest(request),
processingTime, failureCause));
}
}
}很长但是都不是重点：processRequest()方法只是做了一些线程安全的隔离，真正的请求处理，发生在doService()方法中。doService()是将服务器启动时初始化的各种属性设置到request中、然后交由doDispatch处理。FrameworkServlet中的doService()是抽象方法只是一个模版、具体的实现还是在DispatcherServlet中：
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
if (logger.isDebugEnabled()) {
String requestUri = urlPathHelper.getRequestUri(request);
String resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult() ? " resumed" : "";
logger.debug("DispatcherServlet with name '" + getServletName() + "'" + resumed +
" processing " + request.getMethod() + " request for [" + requestUri + "]");
}
// Keep a snapshot of the request attributes in case of an include,
// to be able to restore the original attributes after the include.
Map<String, Object> attributesSnapshot = null;
if (WebUtils.isIncludeRequest(request)) {
logger.debug("Taking snapshot of request attributes before include");
attributesSnapshot = new HashMap<String, Object>();
Enumeration<?> attrNames = request.getAttributeNames();
while (attrNames.hasMoreElements()) {
String attrName = (String) attrNames.nextElement();
if (this.cleanupAfterInclude || attrName.startsWith("org.springframework.web.servlet")) {
attributesSnapshot.put(attrName, request.getAttribute(attrName));
}
}
}
// Make framework objects available to handlers and view objects.
request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
request.setAttribute(THEME_SOURCE_ATTRIBUTE, 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 {
doDispatch(request, response);
}
finally {
if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
return;
}
// Restore the original attribute snapshot, in case of an include.
if (attributesSnapshot != null) {
restoreAttributesAfterInclude(request, attributesSnapshot);
}
}
}
关键部分是几个requet.setAttribute()方法的调用，将前面在初始化流程中实例化的对象设置到http请求的属性中，供下一步处理使用，其中有容器的上下文对象、本地化解析器等SpringMVC特有的编程元素。不同于Struts2中的ValueStack，SpringMVC的数据并没有从HttpServletRequest对象中抽离出来再存进另外一个编程元素，这也跟SpringMVC的设计思想有关。因为从一开始，SpringMVC的设计者就认为，不应该将请求处理过程和Web容器完全隔离。
所以，你可以看到，真正发生请求转发的方法doDispatch()中，它的参数是HttpServletRequest和HttpServletResponse对象。这给我们传递的意思也很明确，从request中能获取到一切请求的数据，从response中，我们又可以往服务器端输出任何响应，Http请求的处理，就应该围绕这两个对象来设计。我们不妨可以将SpringMVC这种设计方案，是从Struts2的过度设计中吸取教训，而向Servlet编程的一种回归和简化。
2.3 doDispatch方法：
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
processedRequest = checkMultipart(request);
multipartRequestParsed = processedRequest != request;
// Determine handler for the current request.
mappedHandler = getHandler(processedRequest, false);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}
// Determine handler adapter for the current request.
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// Process last-modified header, if supported by the handler.
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;
}
}
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
try {
// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
}
applyDefaultViewName(request, mv);
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Error err) {
triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err);
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
// Instead of postHandle and afterCompletion
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
return;
}
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}在这个方法中我们可以看到前面介绍的springMVC关键类或者接口都一一出现在这里：HandlerMapping、HandlerAdapter、ModelAndView、View等等。这个方法整体就是围绕使用HandlerMapping来获取HandlerExcutionChain对象、通过HandlerAdapter来操作HandlerExcutionChain对象获取包含数据的视图、再通过View来解析视图后由DispatcherServlet做出响应。这就是整个请求的处理过程。下面对关键的东西补充点：
2.3.1 到这里我们对HandlerExcutionChain也不是那么陌生、进入源码：
public class HandlerExecutionChain {
private static final Log logger = LogFactory.getLog(HandlerExecutionChain.class);
private final Object handler;
private HandlerInterceptor[] interceptors;
private List<HandlerInterceptor> interceptorList;
private int interceptorIndex = -1;
public HandlerExecutionChain(Object handler) {
this(handler, null);
}
public HandlerExecutionChain(Object handler, HandlerInterceptor[] interceptors) {
if (handler instanceof HandlerExecutionChain) {
HandlerExecutionChain originalChain = (HandlerExecutionChain) handler;
this.handler = originalChain.getHandler();
this.interceptorList = new ArrayList<HandlerInterceptor>();
CollectionUtils.mergeArrayIntoCollection(originalChain.getInterceptors(), this.interceptorList);
CollectionUtils.mergeArrayIntoCollection(interceptors, this.interceptorList);
}
else {
this.handler = handler;
this.interceptors = interceptors;
}
}
public Object getHandler() {
return this.handler;
}
public void addInterceptor(HandlerInterceptor interceptor) {
initInterceptorList();
this.interceptorList.add(interceptor);
}
public void addInterceptors(HandlerInterceptor[] interceptors) {
if (interceptors != null) {
initInterceptorList();
this.interceptorList.addAll(Arrays.asList(interceptors));
}
}
private void initInterceptorList() {
if (this.interceptorList == null) {
this.interceptorList = new ArrayList<HandlerInterceptor>();
}
if (this.interceptors != null) {
this.interceptorList.addAll(Arrays.asList(this.interceptors));
this.interceptors = null;
}
}
public HandlerInterceptor[] getInterceptors() {
if (this.interceptors == null && this.interceptorList != null) {
this.interceptors = this.interceptorList.toArray(new HandlerInterceptor[this.interceptorList.size()]);
}
return this.interceptors;
}
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
if (getInterceptors() != null) {
for (int i = 0; i < getInterceptors().length; i++) {
HandlerInterceptor interceptor = getInterceptors()[i];
if (!interceptor.preHandle(request, response, this.handler)) {
triggerAfterCompletion(request, response, null);
return false;
}
this.interceptorIndex = i;
}
}
return true;
}
void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv) throws Exception {
if (getInterceptors() == null) {
return;
}
for (int i = getInterceptors().length - 1; i >= 0; i--) {
HandlerInterceptor interceptor = getInterceptors()[i];
interceptor.postHandle(request, response, this.handler, mv);
}
}
void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, Exception ex)
throws Exception {
if (getInterceptors() == null) {
return;
}
for (int i = this.interceptorIndex; i >= 0; i--) {
HandlerInterceptor interceptor = getInterceptors()[i];
try {
interceptor.afterCompletion(request, response, this.handler, ex);
}
catch (Throwable ex2) {
logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
}
}
}
void applyAfterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response) {
if (getInterceptors() == null) {
return;
}
for (int i = getInterceptors().length - 1; i >= 0; i--) {
if (interceptors[i] instanceof AsyncHandlerInterceptor) {
try {
AsyncHandlerInterceptor asyncInterceptor = (AsyncHandlerInterceptor) this.interceptors[i];
asyncInterceptor.afterConcurrentHandlingStarted(request, response, this.handler);
}
catch (Throwable ex) {
logger.error("Interceptor [" + interceptors[i] + "] failed in afterConcurrentHandlingStarted", ex);
}
}
}
}
@Override
public String toString() {
if (this.handler == null) {
return "HandlerExecutionChain with no handler";
}
StringBuilder sb = new StringBuilder();
sb.append("HandlerExecutionChain with handler [").append(this.handler).append("]");
if (!CollectionUtils.isEmpty(this.interceptorList)) {
sb.append(" and ").append(this.interceptorList.size()).append(" interceptor");
if (this.interceptorList.size() > 1) {
sb.append("s");
}
}
return sb.toString();
}
}
a） .拦截器组成的列表，在执行对象被调用的前后，会依次执行。这里可以看成是一个的AOP环绕通知，拦截器可以对处理对象随心所欲的进行处理和增强。这里明显是吸收了Struts2中拦截器的设计思想。这种AOP环绕式的扩展点设计，也几乎成为所有框架必备的内容。
b） .实际的处理对象，即handler对象，是由Object对象来引用的。 private final Object handler;之所以要用一个java世界最基础的Object对象引用来引用这个handler对象，是因为连特定的接口也不希望绑定在这个handler对象上，从而使handler对象具有最大程度的选择性和灵活性。
2.3.2 实际执行handler ： mv =ha.handle(processedRequest, response, mappedHandler.getHandler());
有兴趣的可以自己跟一下。处理到最后返回ModelAndView的类：RequestMappingHandlerAdapter）——
private ModelAndView getModelAndView(ModelAndViewContainer mavContainer,
ModelFactory modelFactory, NativeWebRequest webRequest) throws Exception {
modelFactory.updateModel(webRequest, mavContainer);
if (mavContainer.isRequestHandled()) {
return null;
}
ModelMap model = mavContainer.getModel();
ModelAndView mav = new ModelAndView(mavContainer.getViewName(), model);
if (!mavContainer.isViewReference()) {
mav.setView((View) mavContainer.getView());
}
if (model instanceof RedirectAttributes) {
Map<String, ?> flashAttributes = ((RedirectAttributes) model).getFlashAttributes();
HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);
RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes);
}
return mav;
}然后经过一系列的Handlerinteceptor处理 处理被handler和handler adapter处理的result。最后将解析结果View返回给DispatcherServlet、
补充：
这里只是从抽象的角度来分析了一个请求的处理过程、具体的细节则是不同的实现类有不同的实现方式、不再过度关注、对源码的了解也是对设计者的思想的一种了解、随着时间的推移、各种各样的框架会层出不穷、但是万变不离其宗、掌握了最基础、最核心的东西、在接触新东西时就能更加的从容一点。并且不同框架之间也有些许相通的地方、比如springMVC的过滤器与struts2中是如此的相似、但是springMVC的过滤器多了一个完成之后的操作、同时也允许自己去扩展等等等等。到现在也告一小段落、总体的体会是：学习一个框架、理解设计思想、设计模式是非常重要的、还有对类的说明都是直接为我们展示设计者想要实现或者达到的目的。没事多看看官方文档、英文还是硬伤、但是不看永远都不会、看了、坚持下来、总有认识他的时候。
更多内容： springMVC系列之目录——00
最后
以上就是平常大侠为你收集整理的springMVC系列源码之请求处理过程——12springMVC系列源码之请求处理过程——12的全部内容，希望文章能够帮你解决springMVC系列源码之请求处理过程——12springMVC系列源码之请求处理过程——12所遇到的程序开发问题。
如果觉得靠谱客网站的内容还不错，欢迎将靠谱客网站推荐给程序员好友。
本图文内容来源于网友提供，作为学习参考使用，或来自网络收集整理，版权属于原作者所有。
发表评论 取消回复