------------吾亦无他,唯手熟尔，谦卑若愚，好学若饥-------------
先从概念理解，从*调度器，携带参数request，调度到HandleMapping处理器映射器，处理器映射器返回处理器执行链给*调度器
我从底层走一遍，印证这个概念：
1.都说是*调度器的，所以先找到*调度器DispatcherServlet
2.从他里面找到一个方法 ctrl+f 找（doDistch）
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 err = null;
Exception dispatchException = null;
try {
processedRequest = this.checkMultipart(request);
multipartRequestParsed = processedRequest != request;
mappedHandler = this.getHandler(processedRequest);
if(mappedHandler == null || mappedHandler.getHandler() == null) {
this.noHandlerFound(processedRequest, response);
return;
}
HandlerAdapter ex = this.getHandlerAdapter(mappedHandler.getHandler());
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if(isGet || "HEAD".equals(method)) {
long lastModified = ex.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;
}
}
if(!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
err = ex.handle(processedRequest, response, mappedHandler.getHandler());
if(asyncManager.isConcurrentHandlingStarted()) {
return;
}
this.applyDefaultViewName(processedRequest, err);
mappedHandler.applyPostHandle(processedRequest, response, err);
} catch (Exception var19) {
dispatchException = var19;
}
this.processDispatchResult(processedRequest, response, mappedHandler, err, dispatchException);
} catch (Exception var20) {
this.triggerAfterCompletion(processedRequest, response, mappedHandler, var20);
} catch (Error var21) {
this.triggerAfterCompletionWithError(processedRequest, response, mappedHandler, var21);
}
} finally {
if(asyncManager.isConcurrentHandlingStarted()) {
if(mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
} else if(multipartRequestParsed) {
this.cleanupMultipart(processedRequest);
}
}
}
这个方法里面很多内容不需要关注，需要关注的的我讲讲
HttpServletRequest processedRequest = request;
//接收请求
HandlerExecutionChain mappedHandler = null;
//处理器执行链
boolean multipartRequestParsed = false;
//多部分请求，文件上传
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
//异部请求 try {
try { ModelAndView err = null;
//视图解析 try { processedRequest = this.checkMultipart(request);
//检查是否是多部分请求
multipartRequestParsed = processedRequest != request; mappedHandler = this.getHandler(processedRequest);
//这就返回处理器执行链
3.到这儿，点击getHandler（processedRequest）查看
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
Iterator var2 = this.handlerMappings.iterator();
HandlerExecutionChain handler;
do {
if(!var2.hasNext()) {
return null;
}
HandlerMapping hm = (HandlerMapping)var2.next();
if(this.logger.isTraceEnabled()) {
this.logger.trace("Testing handler map [" + hm + "] in DispatcherServlet with name \'" + this.getServletName() + "\'");
}
handler = hm.getHandler(request);
} while(handler == null);
return handler;
}
我把关键代码提炼出来解释一波
//迭代器，没做泛型，handlerMapping是list集合
Iterator var2 = this.handlerMappings.iterator();
//处理器执行链
HandlerExecutionChain handler;
do {
if(!var2.hasNext()) {
return null;
}
//处理器映射器
HandlerMapping hm = (HandlerMapping)var2.next(); //继续追踪
handler = hm.getHandler(request);
} while(handler == null); return handler;
4.追踪hm.getHandler(request)方法，发现他是HandlerMapping接口的，（Ctrl+H）找它的实现类AbstractHandlerMapping,ctrl+F找getHandler
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
Object handler = this.getHandlerInternal(request);
if(handler == null) {
handler = this.getDefaultHandler();
}
if(handler == null) {
return null;
} else {
if(handler instanceof String) {
String executionChain = (String)handler;
handler = this.getApplicationContext().getBean(executionChain);
}
HandlerExecutionChain executionChain1 = this.getHandlerExecutionChain(handler, request);
if(CorsUtils.isCorsRequest(request)) {
CorsConfiguration globalConfig = this.corsConfigSource.getCorsConfiguration(request);
CorsConfiguration handlerConfig = this.getCorsConfiguration(handler, request);
CorsConfiguration config = globalConfig != null?globalConfig.combine(handlerConfig):handlerConfig;
executionChain1 = this.getCorsHandlerExecutionChain(request, executionChain1, config);
}
return executionChain1;
}
}
同样，我把关键代码提出来解释一波
//获取处理器
Object handler = this.getHandlerInternal(request);
//处理器为空就用默认的
if(handler == null) {
handler = this.getDefaultHandler();
}
//默认的也是空就返回null
if(handler == null) {
return null;
} else {
//判断是否是String类型
if(handler instanceof String) {
//这儿就是我们一般用的处理器的从配置文件bean的id
String handlerName = (String)handler; // /hello
//这就是Spring啊
handler = this.getApplicationContext().getBean(handlerName);
}
//获取处理程序执行链
HandlerExecutionChain executionChain1 = this.getHandlerExecutionChain(handler, request);
//返回的时候变成携带处理器的了
return this.getHandlerExecutionChain(handler, request); }
5.追踪获取程序执行链,this.getHandlerExecutionChain(handler,request)
protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
//三元表达式，是处理器执行链就强转，不是就获取根据处理器生成一个
HandlerExecutionChain chain = handler instanceof HandlerExecutionChain?(HandlerExecutionChain)handler:new HandlerExecutionChain(handler);
String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
Iterator var5 = this.adaptedInterceptors.iterator();
while(var5.hasNext()) {
//只需要知道这儿添加拦截器即可
HandlerInterceptor interceptor = (HandlerInterceptor)var5.next();
if(interceptor instanceof MappedInterceptor) {
MappedInterceptor mappedInterceptor = (MappedInterceptor)interceptor;
if(mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
chain.addInterceptor(mappedInterceptor.getInterceptor());
}
} else {
chain.addInterceptor(interceptor);
}
}
return chain;
}