多个拦截器的执行流程：
1、applyPreHandle方法。按照配置的顺序执行拦截其中的preHandle方法，并记下最后放行的拦截器的索引。如果都放行则不执行applyPreHandle方法中对应拦截器的afterCompletion函数的方法；只要有一个拦截器不放行，按照之前记录的索引倒序执行applyPreHandle方法中对应拦截器的afterCompletion函数的方法，下面的所有步骤都不执行。
2、handle方法。执行目标方法。若目标方法没有发生异常，正常执行下面的方法；如果该方法发生异常，则在doDispatch方法里面会catch到并按照之前记录的索引倒序执行handle方法中对应拦截器的afterCompletion函数的方法，而且不会执行后面的方法(拦截器的postHandle方法和渲染页面方法)。
3、applyPostHandle方法。倒序执行拦截器的postHandle方法。
4、processDispatchResult方法。若目标方法没有发生异常，目标方法最后会按照之前记录的索引倒序执行processDispatchResult方法中拦截器的afterCompletion函数的方法；如果该方法发生异常，则在doDispatch方法里面会catch到并按照之前记录的索引倒序执行拦截器的afterCompletion方法。
接受源码的制裁吧
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 {
processedRequest = this.checkMultipart(request);
multipartRequestParsed = processedRequest != request;
mappedHandler = this.getHandler(processedRequest);
if (mappedHandler == null) {
this.noHandlerFound(processedRequest, response);
return;
}
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 ((new ServletWebRequest(request, response)).checkNotModified(lastModified) && isGet) {
return;
}
}
//调用拦截器的preHandle方法
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
this.applyDefaultViewName(processedRequest, mv);
//调用拦截器的postHandle方法
mappedHandler.applyPostHandle(processedRequest, response, mv);
} catch (Exception var20) {
dispatchException = var20;
} catch (Throwable var21) {
dispatchException = new NestedServletException("Handler dispatch failed", var21);
}
this.processDispatchResult(processedRequest, response, mappedHandler, mv, (Exception)dispatchException); //页面渲染
} 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);
}
}
}
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
HandlerInterceptor[] interceptors = this.getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for(int i = 0; i < interceptors.length; this.interceptorIndex = i++) { //拦截器的preHandle方法返回true的时候顺带记录索引
HandlerInterceptor interceptor = interceptors[i];
if (!interceptor.preHandle(request, response, this.handler)) { //一旦有个前置处理器没放行, 执行拦截器的afterCompletion方法
this.triggerAfterCompletion(request, response, (Exception)null);
return false;
}
}
}
return true;
}
void applyPostHandle(HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv) throws Exception {
HandlerInterceptor[] interceptors = this.getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for(int i = interceptors.length - 1; i >= 0; --i) {
HandlerInterceptor interceptor = interceptors[i];
interceptor.postHandle(request, response, this.handler, mv);
}
}
}
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response, @Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv, @Nullable Exception exception) throws Exception {
boolean errorView = false;
if (exception != null) {
if (exception instanceof ModelAndViewDefiningException) {
this.logger.debug("ModelAndViewDefiningException encountered", exception);
mv = ((ModelAndViewDefiningException)exception).getModelAndView();
} else {
Object handler = mappedHandler != null ? mappedHandler.getHandler() : null;
mv = this.processHandlerException(request, response, handler, exception);
errorView = mv != null;
}
}
if (mv != null && !mv.wasCleared()) {
this.render(mv, request, response); //页面炸了就不会执行下面的方法, 但会在doDispatch方法catch出来执行拦截器的afterCompletion方法
if (errorView) {
WebUtils.clearErrorRequestAttributes(request);
}
} else if (this.logger.isTraceEnabled()) {
this.logger.trace("No view rendering, null ModelAndView returned.");
}
if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
if (mappedHandler != null) {
mappedHandler.triggerAfterCompletion(request, response, (Exception)null);
}
}
}
void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, @Nullable Exception ex) throws Exception {
HandlerInterceptor[] interceptors = this.getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for(int i = this.interceptorIndex; i >= 0; --i) { //根据索引倒叙遍历
HandlerInterceptor interceptor = interceptors[i];
try {
interceptor.afterCompletion(request, response, this.handler, ex);
} catch (Throwable var8) {
logger.error("HandlerInterceptor.afterCompletion threw exception", var8);
}
}
}
}
