SpringBoot 中DispatcherServlet请求分发流程源码分析
以一个简单的请求为例（实际RedisController包含多个请求）
@RestController
@RequestMapping("/redis")
public class RedisController {
@RequestMapping(value = {"/getmsg"})
public String getmsg(){
return "hello";
}
.....
}
整个 DispatcherServlet执行流程：
正常情况下整个request流程代码都在DispatcherServlet#doService()方法中执行，由同一个线程完成从请求到响应
FrameworkServlet#doPost/doGet
FrameworkServlet#processRequest
DispatcherServlet#doService
DispatcherServlet#doDispatch
doDispatch是SpringMvc中的核心请求处理方法，几乎全部的请求处理流程都在这个方法中。下图就是doDispatch方法的主要执行流程。
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);//是否上传文件
multipartRequestParsed = (processedRequest != request);
//根据request信息Uri找到对应HandlerExecutionChain执行链
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null) {
//没有找到HandlerExecutionChain 的通过response反馈
noHandlerFound(processedRequest, response);
return;
}
//通过已找到的Handler取得HandlerAdapter
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
//缓存
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
//pre拦截器执行
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
//执行handle，Controller方法
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
applyDefaultViewName(processedRequest, mv);
//post拦截器执行（倒序）
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}
catch (Throwable err) {
// As of 4.3, we're processing Errors thrown from handler methods as well,
// making them available for @ExceptionHandler methods and other scenarios.
dispatchException = new NestedServletException("Handler dispatch failed", err);
}
//页面跳转，响应信息
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Throwable err) {
triggerAfterCompletion(processedRequest, response, mappedHandler,
new NestedServletException("Handler processing failed", err));
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
// Instead of postHandle and afterCompletion
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
}
else {
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
}DispatcherServlet#getHandler
可以看到springboot启动时装载的全部handlerMapping都保存在List<HandlerMapping> handlerMappings中。这里遍历handlerMappings中所有handlerMapping，直到找到请求对应的Mapping并返回执行立链HandlerExecutionChain。因为是@RequestMapping映射，所以遍历到handlerMappings[1]==RequestMappingHandlerMapping可以找到对应执行链。
下边直接步进到RequestMappingHandlerMapping其继承自AbstractHandlerMapping。
RequestMappingHandlerMapping初始化时注册@RequestMapping映射
https://blog.csdn.net/shanchahua123456/article/details/89816167
RequestMappingHandlerMapping成员变量
AbstractHandlerMapping#getHandler
AbstractHandlerMethodMapping#getHandlerInternal
AbstractHandlerMethodMapping其继承自AbstractHandlerMapping，实现了getHandlerInternal()。
这里取得mappingRegistry的读锁，后续就是通过URL从mappingRegistry匹配HandlerMethod(执行方法)。
mappingRegistry中注册了SpringMvc的控制器和HandlerMethod，以及URL的映射关系。下面有mappingRegistry的成员变量介绍。
AbstractHandlerMethodMapping#lookupHandlerMethod
AbstractHandlerMethodMapping.MappingRegistry#getMappingsByUrl
到这里可以看到通过urlPath从urlLookUp中找到
返回List<RequestMappingInfo>
AbstractHandlerMethodMapping#lookupHandlerMethod
AbstractHandlerMethodMapping#addMatchingMappings
RequestMappingInfoHandlerMapping#getMatchingMapping
AbstractHandlerMethodMapping.MappingRegistry#getMappings
AbstractHandlerMethodMapping#addMatchingMappings
到这里可以看到Spring已经通过mappingRegistry匹配到URL对应HandlerMethod对象，其成员变量包括： Bean对象，Method对象，参数列表等信息。将匹配到的HandlerMethod对象等信息保存到matches中。
mappingRegistry
mappingRegistry对象中成员变量：各种Map还有一个读写锁。
mappingRegistry的各个主要变量
返回 AbstractHandlerMethodMapping#lookupHandlerMethod
返回lookupHandlerMethod()中从返回的List<Match> matches中匹配最合适的handlerMethod返回getHandlerInternal()方法。
if (!matches.isEmpty()) {
Comparator<Match> comparator = new MatchComparator(getMappingComparator(request));
matches.sort(comparator);
Match bestMatch = matches.get(0);
if (matches.size() > 1) {
if (logger.isTraceEnabled()) {
logger.trace(matches.size() + " matching mappings: " + matches);
}
if (CorsUtils.isPreFlightRequest(request)) {
return PREFLIGHT_AMBIGUOUS_MATCH;
}
Match secondBestMatch = matches.get(1);
if (comparator.compare(bestMatch, secondBestMatch) == 0) {
Method m1 = bestMatch.handlerMethod.getMethod();
Method m2 = secondBestMatch.handlerMethod.getMethod();
String uri = request.getRequestURI();
throw new IllegalStateException(
"Ambiguous handler methods mapped for '" + uri + "': {" + m1 + ", " + m2 + "}");
}
}
handleMatch(bestMatch.mapping, lookupPath, request);
return bestMatch.handlerMethod;
}返回 AbstractHandlerMethodMapping#getHandlerInternal
此时已取得 handlerMethod。
返回 AbstractHandlerMapping#getHandler
此时已取得 handlerMethod，剩下的工作是完成执行链HandlerExecutionChain
取得执行链HandlerExecutionChain
AbstractHandlerMapping#getHandlerExecutionChain
创建HandlerExecutionChain(handler)，遍历ArrayList<HandlerInterceptor> adaptedInterceptors把interceptor加入其中。
返回AbstractHandlerMapping#getHandler
返回DispatcherServlet#getHandler
此时已取得完整执行链，回到最初的DispatcherServlet类中。
可以看到IDE提示HandlerExecutionChain handler中包含HandlerMethod和两个拦截器
返回DispatcherServlet#doDispatch
取得执行链HandlerExecutionChain 后，取得HandlerAdapter。
HandlerExecutionChain#getHandler
上图mappedHandler为之前取得的执行链HandlerExecutionChain ，取得执行链中的handler。
DispatcherServlet#getHandlerAdapter
遍历handlerAdapters找到合适。
返回DispatcherServlet#doDispatch
此时回到doDispatch方法，已经获得HandlerExecutionChain和HandlerAdapter。剩下的流程执行前置拦截器，执行Controller，执行post拦截器。
HandlerExecutionChain mappedHandler执行pre拦截器
HandlerExecutionChain#applyPreHandle
执行PRE拦截器，此处将当前执行链中的(HandlerMethod)this.handler传入拦截器。
返回DispatcherServlet#doDispatch
继续执行Controller方法(Handler)
AbstractHandlerMethodAdapter#handle
RequestMappingHandlerAdapter#handleInternal
RequestMappingHandlerAdapter#invokeHandlerMethod
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ServletWebRequest webRequest = new ServletWebRequest(request, response);
//webRequest : uri=/redis/getmsg;client=127.0.0.1
try {
WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
if (this.argumentResolvers != null) {
invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
}
if (this.returnValueHandlers != null) {
invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
}
invocableMethod.setDataBinderFactory(binderFactory);
invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);
ModelAndViewContainer mavContainer = new ModelAndViewContainer();
mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
modelFactory.initModel(webRequest, mavContainer, invocableMethod);
mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);
AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
asyncWebRequest.setTimeout(this.asyncRequestTimeout);
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
asyncManager.setTaskExecutor(this.taskExecutor);
asyncManager.setAsyncWebRequest(asyncWebRequest);
asyncManager.registerCallableInterceptors(this.callableInterceptors);
asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);
if (asyncManager.hasConcurrentResult()) {
Object result = asyncManager.getConcurrentResult();
mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];
asyncManager.clearConcurrentResult();
LogFormatUtils.traceDebug(logger, traceOn -> {
String formatted = LogFormatUtils.formatValue(result, !traceOn);
return "Resume with async result [" + formatted + "]";
});
invocableMethod = invocableMethod.wrapConcurrentResult(result);
}
invocableMethod.invokeAndHandle(webRequest, mavContainer);
if (asyncManager.isConcurrentHandlingStarted()) {
return null;
}
return getModelAndView(mavContainer, modelFactory, webRequest);
}
finally {
webRequest.requestCompleted();
}
}
最终会走到此方法中InvocableHandlerMethod#doInvoke
通过HandlerMethod中的BridgedMethod反射执行Controller中的@RequestMapping映射方法调用。
getBridgedMethod().invoke(getBean(), args);getBridgedMethod()返回的是HandlerMethod中的bridgedMethod（下图）。
getBean()返回的是HandlerMethod中的bean（下图）。
RedisController#getmsg
此时通过放射调用，执行真正的RedisController中的@RequestMapping映射方法
一直返回到ServletInvocableHandlerMethod#invokeAndHandle
ModelAndViewContainer mavContainer: View is [null]; default model {} 因为是@RestController，View=null
returnValue="hello"
RequestMappingHandlerAdapter#invokeHandlerMethod
通过getModelAndView()将mavContainer转换成ModelAndView返回
一直返回DispatcherServlet#doDispatch
Controller@RequestMapping映射方法执行完毕，返回MV。向下执行POST拦截器。
HandlerExecutionChain#applyPostHandle
倒序执行Post拦截器（后进先出）
响应用户请求DispatcherServlet#processDispatchResult
