正文
spring mvc之请求过程源码分析
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简介
上一篇，我们分析了spring mvc启动过程的源码，这一节，来一起分析下在用户请求controller的过程中，spring mvc做了什么事？
一、准备
我写这么一个controller
package com.jacky.controller; import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.method.HandlerMethod; @Controller
@RequestMapping("/bbb")
public class IndexController { @RequestMapping(value = "/test.do", method = RequestMethod.GET)
public String index() {
return "index";
} @RequestMapping(value = "/aaa.do", method = RequestMethod.GET)
@ResponseBody
public String aaa() {
return "aaa";
} }
二、用户请求controller的过程（http://localhost:8080/spring-mvc-demo/bbb/aaa.do）
上一篇，我们知道了，spring mcv基于servlet的，核心类是DispatcherServlet，那根据Servlet的知识，请求首先service()方法，但是在 DispatherServlet 中并没有找到service方法，在其父类FrameworkServlet中找到service方法，那我们就从这里看起。
protected void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { HttpMethod httpMethod = HttpMethod.resolve(request.getMethod());
if (HttpMethod.PATCH == httpMethod || httpMethod == null) {
processRequest(request, response);
}
else {
super.service(request, response);
}
}
2.1、接下来我们看处理请求方法processRequest(request, response)
protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doService(request, response);
}
2.2、接下来我们看看doService(request,response)方法
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
doDispatch(request, response);
}
2.3、接下来我们看看DispatcherServlet的doDispatch(request,reponse)方法
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
ModelAndView mv = null;
Exception dispatchException = null;
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
//根据请求获得请求执行链
mappedHandler = getHandler(processedRequest);
//根据处理器获得对应的适配器
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
//调用controller中的method的方法之前先调用拦截器的preHandle方法
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
//根据请求调用controller中的method，然后返回ModelAndView
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
//调用spring mvc拦截器的postHandle方法
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
这个方法里面有很多很关键的方法，没事我们一个个看里面的实现细节
2.4、首先我们看看获得请求执行链的方法getHandler(processedRequest)
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
//遍历spring mvc启动时初始化好的handlerMappings（类型为List<HandlerMapping>）
for (HandlerMapping hm : this.handlerMappings) {
//利用handlerMaping取得处理器执行链
HandlerExecutionChain handler = hm.getHandler(request);
if (handler != null) {
return handler;
}
}
return null;
}
2.5、接下来我们看看handlerMaping是怎么取得处理器执行链的？
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
//获得HandlerMethod对象
Object handler = getHandlerInternal(request);
//获得处理器执行链对象
HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
return executionChain;
}
2.6、首先我来看看怎么获得HandleMethod对象的
protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
//获得请求路径,这里是lookupPath="/bbb/aaa.do"
String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
//开启读锁
this.mappingRegistry.acquireReadLock();
try {
//根据url获得HandleMethod
HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);
return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);
}
finally {
//释放读锁
this.mappingRegistry.releaseReadLock();
}
}
2.7、接下来我们看看getHandlerExecutionChain是怎么获得处理器执行链的
protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?
(HandlerExecutionChain) handler : new HandlerExecutionChain(handler));
String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
for (HandlerInterceptor interceptor : this.adaptedInterceptors) {
if (interceptor instanceof MappedInterceptor) {
MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor;
if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
//往处理器执行链的List<HandlerInterceptor>类型的interceptorList集合中，存放拦截器
chain.addInterceptor(mappedInterceptor.getInterceptor());
}
}
else {
chain.addInterceptor(interceptor);
}
}
return chain;
}
从这里我们可以看到处理器其实封装了拦截器集合和一个handleMethod对象（封装了controller Class对象，浏览器请求的Controler中的method方法对象，参数）
2.8、上面，我们知道了，springMVC是怎么通过handleMaping获得handle（HandleMethod）对象,以及怎么添加拦截器，组装成处理器执行链，接下来我们继续看看springMVC是怎么获得处理器对应的
适配器的。
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
//遍历spring mvc初始化时，设置的DispatcherServlet的成员变量List<HandlerAdapter> handlerAdapters
for (HandlerAdapter ha : this.handlerAdapters) {
//判断适配器支不支持handler
if (ha.supports(handler)) {
return ha;
}
}
throw new ServletException("No adapter for handler [" + handler +
"]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
}
因为有会遍历很多种适配器，从上面我们知道，handlerd的类型是HandleMethod,所以的我们看的是RequestMappingHandlerAdapter适配器，根据RequestMappingHandlerAdapter的继承关系
可以知道，RequestMappingHandlerAdapter继承了AbstractHandlerMethodAdapter,在ha.supports(handler)方法中，刚好在AbstractHandlerMethodAdapter类中，我们来看看
public final boolean supports(Object handler) {
return (handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler));
}
就是判断传入的handler是否是属于HandlerMethod类型的，如果是，就返回true，然后RequestMappingHandlerAdapter对象
2.9、springMVC怎么获得处理请求的适配器我们看完了，接下来，我们看看，获得适配器后，是怎么调用到controller中的对应的method的？
//根据请求调用controller中的method，然后返回ModelAndView
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
首先调用的是AbstractHandlerMethodAdapter类的handle方法
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception { return handleInternal(request, response, (HandlerMethod) handler);
}
可以看到这个方法没干什么，只是调用了handleInternal方法，那我们就看看这个方法
protected ModelAndView handleInternal(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ModelAndView mav;
mav = invokeHandlerMethod(request, response, handlerMethod);
return mav;
}
这个方法主要是调了invokeHandlerMethod方法，那我们继续来看卡这个方法干了什么？
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception { ServletWebRequest webRequest = new ServletWebRequest(request, response);
try {
WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory); //把handlerMethod封装成ServletInvocableHandlerMethod
ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
//设置参数解析器
invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
//设置spring mvc请求controller的method返回值处理器
invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
invocableMethod.setDataBinderFactory(binderFactory);
//设置参数名称发现器
invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer); ModelAndViewContainer mavContainer = new ModelAndViewContainer();
mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
modelFactory.initModel(webRequest, mavContainer, invocableMethod);
mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);
invocableMethod.invokeAndHandle(webRequest, mavContainer);
return getModelAndView(mavContainer, modelFactory, webRequest);
}
finally {
webRequest.requestCompleted();
}
}
3.0、接下来我们看看真正的调用和处理方法invocableMethod.invokeAndHandle(webRequest, mavContainer);
public void invokeAndHandle(ServletWebRequest webRequest,
ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception {
//在这里通过反射调用controller中的method方法
Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
setResponseStatus(webRequest); if (returnValue == null) {
if (isRequestNotModified(webRequest) || hasResponseStatus() || mavContainer.isRequestHandled()) {
mavContainer.setRequestHandled(true);
return;
}
} else if (StringUtils.hasText(this.responseReason)) {
mavContainer.setRequestHandled(true);
return;
} mavContainer.setRequestHandled(false);
//在这里通过返回值处理器处理器进行二次处理，例如：如果加了方法加了reponseBody注解，就把结果序列化json字符串再返回
this.returnValueHandlers.handleReturnValue(
returnValue, getReturnValueType(returnValue), mavContainer, webRequest); }
