上一篇文章：Spring MVC 拦截器（HandlerInterceptor）使用 介绍了 Spring MVC HandlerInterceptor的使用和应用场景，本篇中我们将结合Spring MVC 源码来研究一下其内部实现。
本文分析使用Spring Framework源码 为 Spring Framework 4.3.4.RELEASE 。
首先，我们看一下 org.springframework.web.servlet.DispatcherServlet 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);
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()) {
logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
}
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
//调用已注册HandlerInterceptor的preHandle()方法
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// 真正执行Controller对应的方法
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
applyDefaultViewName(processedRequest, mv);
//调用已注册HandlerInterceptor的postHandle()方法
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);
}
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
//调用已注册HandlerInterceptor的afterCompletion()方法
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Throwable err) {
//调用已注册HandlerInterceptor的afterCompletion()方法
triggerAfterCompletion(processedRequest, response, mappedHandler,
new NestedServletException("Handler processing failed", err));
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
// Instead of postHandle and afterCompletion
if (mappedHandler != null) {
//调用已注册HandlerInterceptor的afterConcurrentHandlingStarted()方法
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
}
else {
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
}
/**
* Handle the result of handler selection and handler invocation, which is
* either a ModelAndView or an Exception to be resolved to a ModelAndView.
*/
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {
boolean errorView = false;
if (exception != null) {
if (exception instanceof ModelAndViewDefiningException) {
logger.debug("ModelAndViewDefiningException encountered", exception);
mv = ((ModelAndViewDefiningException) exception).getModelAndView();
}
else {
Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
mv = processHandlerException(request, response, handler, exception);
errorView = (mv != null);
}
}
// Did the handler return a view to render?
if (mv != null && !mv.wasCleared()) {
render(mv, request, response);
if (errorView) {
WebUtils.clearErrorRequestAttributes(request);
}
}
else {
if (logger.isDebugEnabled()) {
logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +
"': assuming HandlerAdapter completed request handling");
}
}
if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
// Concurrent handling started during a forward
return;
}
if (mappedHandler != null) {
//调用已注册HandlerInterceptor的afterCompletion()方法
mappedHandler.triggerAfterCompletion(request, response, null);
}
}
接着，我们来看看 HandlerExecutionChain的applyPreHandle方法实现：
/**
* 执行注册到该请求上的所有HandlerInterceptor的 preHandle 方法
*/
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for (int i = 0; i < interceptors.length; i++) {
HandlerInterceptor interceptor = interceptors[i];
if (!interceptor.preHandle(request, response, this.handler)) {
triggerAfterCompletion(request, response, null);
return false;
}
this.interceptorIndex = i;
}
}
return true;
}
public HandlerInterceptor[] getInterceptors() {
if (this.interceptors == null && this.interceptorList != null) {
this.interceptors = this.interceptorList.toArray(new HandlerInterceptor[this.interceptorList.size()]);
}
return this.interceptors;
}
HandlerExecutionChain的applyPostHandle方法实现：
/**
* 执行注册到该请求上的所有HandlerInterceptor的 postHandle 方法
*/
void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv) throws Exception {
HandlerInterceptor[] interceptors = 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);
}
}
}
HandlerExecutionChain的triggerAfterCompletion方法实现：
/**
* 执行注册到该请求上的所有HandlerInterceptor的 afterCompletion 方法
*/
void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, Exception ex)
throws Exception {
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for (int i = this.interceptorIndex; i >= 0; i--) {
HandlerInterceptor interceptor = interceptors[i];
try {
interceptor.afterCompletion(request, response, this.handler, ex);
}
catch (Throwable ex2) {
logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
}
}
}
}
最后，HandlerExecutionChain的applyAfterConcurrentHandlingStarted方法实现：
/**
* 执行注册到该请求上的所有AsyncHandlerInterceptor的 afterConcurrentHandlingStarted 方法
*/
void applyAfterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response) {
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for (int i = interceptors.length - 1; i >= 0; i--) {
if (interceptors[i] instanceof AsyncHandlerInterceptor) {
try {
AsyncHandlerInterceptor asyncInterceptor = (AsyncHandlerInterceptor) interceptors[i];
asyncInterceptor.afterConcurrentHandlingStarted(request, response, this.handler);
}
catch (Throwable ex) {
logger.error("Interceptor [" + interceptors[i] + "] failed in afterConcurrentHandlingStarted", ex);
}
}
}
}
}
上述方法我都加上注释，而且代码也比较好理解，我就不废话了。
接下来，HandlerExecutionChain 内部的Interceptor数组是在什么时候初始化的呢？
来看看 HandlerExecutionChain 类的定义，源码如下：
package org.springframework.web.servlet;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.util.CollectionUtils;
import org.springframework.util.ObjectUtils;
public class HandlerExecutionChain {
private static final Log logger = LogFactory.getLog(HandlerExecutionChain.class);
private final Object handler;
private HandlerInterceptor[] interceptors;
private List interceptorList;
private int interceptorIndex = -1;
public HandlerExecutionChain(Object handler) {
this(handler, (HandlerInterceptor[]) null);
}
public HandlerExecutionChain(Object handler, HandlerInterceptor... interceptors) {
if (handler instanceof HandlerExecutionChain) {
HandlerExecutionChain originalChain = (HandlerExecutionChain) handler;
this.handler = originalChain.getHandler();
this.interceptorList = new ArrayList();
CollectionUtils.mergeArrayIntoCollection(originalChain.getInterceptors(), this.interceptorList);
CollectionUtils.mergeArrayIntoCollection(interceptors, this.interceptorList);
}
else {
this.handler = handler;
this.interceptors = interceptors;
}
}
/**
* 向handler中添加interceptor
*/
public void addInterceptor(HandlerInterceptor interceptor) {
initInterceptorList().add(interceptor);
}
/**
* 向handler中添加多个interceptor
*/
public void addInterceptors(HandlerInterceptor... interceptors) {
if (!ObjectUtils.isEmpty(interceptors)) {
initInterceptorList().addAll(Arrays.asList(interceptors));
}
}
private List initInterceptorList() {
if (this.interceptorList == null) {
this.interceptorList = new ArrayList();
if (this.interceptors != null) {
// An interceptor array specified through the constructor
this.interceptorList.addAll(Arrays.asList(this.interceptors));
}
}
this.interceptors = null;
return this.interceptorList;
}
/**
* 按顺序返回handler上的HandlerInterceptor列表
*/
public HandlerInterceptor[] getInterceptors() {
if (this.interceptors == null && this.interceptorList != null) {
this.interceptors = this.interceptorList.toArray(new HandlerInterceptor[this.interceptorList.size()]);
}
return this.interceptors;
}
}
HandlerExecutionChain 提供了addInterceptors()方法来添加HandlerInterceptor，那addInterceptors是在哪里被调用的呢？
我们回到DispatcherServlet 的 doDispatch方法中，如下：
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);
// 获取当前请求对应的handler
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}
...
}
catch (Exception ex) {
dispatchException = ex;
}
catch (Throwable err) {
...
}
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 {
...
}
}
/**
* 获取当前请求对应的HandlerExecutionChain
*/
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
for (HandlerMapping hm : this.handlerMappings) {
if (logger.isTraceEnabled()) {
logger.trace(
"Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");
}
HandlerExecutionChain handler = hm.getHandler(request);
if (handler != null) {
return handler;
}
}
return null;
}
接着来看看HandlerMapping 的getHandler(request)方法，HandlerMapping是一个接口，getHandler(request)方法是在AbstractHandlerMapping中实现的，如下：
@Override
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
//获取请求对应的handler
Object handler = getHandlerInternal(request);
if (handler == null) {
handler = getDefaultHandler();
}
if (handler == null) {
return null;
}
// Bean name or resolved handler?
if (handler instanceof String) {
String handlerName = (String) handler;
handler = getApplicationContext().getBean(handlerName);
}
//根据handler构造HandlerExecutionChain
HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
if (CorsUtils.isCorsRequest(request)) {
CorsConfiguration globalConfig = this.corsConfigSource.getCorsConfiguration(request);
CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
}
return executionChain;
}
/**
* 构造HandlerExecutionChain, 并初始化HandlerInterceptor
*/
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)) {
chain.addInterceptor(mappedInterceptor.getInterceptor());
}
}
else {
chain.addInterceptor(interceptor);
}
}
return chain;
}
源码分析到这里就结束了。