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Interceptor拦截器用于拦截Controller层接口，表现形式有点像Spring的AOP，但是AOP是针对单一的方法。Interceptor是针对Controller接口以及可以处理request和response对象。
1 HandlerInterceptor接口的定义
我们先来看下HandlerInterceptor接口的定义，定义了三个接口，分别是preHandle、postHandle、afterCompletion。
public interface HandlerInterceptor {
boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception;
void postHandle(
HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView)
throws Exception;
void afterCompletion(
HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
throws Exception;
}preHandle是调用Controller之前被调用，当返回false后，会跳过之后的拦截器，并且不会执行所有拦截器的postHandle，并调用返回true的拦截器的afterCompletion方法。
postHandle是调用Controller之后被调用，但是在渲染View页面之前。
afterCompletion是调用完Controller接口，渲染View页面最后调用。返回true的拦截器都会调用该拦截器的afterCompletion方法，顺序相反。
和HandlerInterceptor很相似的要有一个AsyncHandlerInterceptor接口，只是多了个afterConcurrentHandlingStarted个方法，当接口使用了异步的方法的时候调用。
public interface AsyncHandlerInterceptor extends HandlerInterceptor {
void afterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception;
}
2 HandlerInterceptor接口的定义
2.1 DispatcherServlet里doDispatch主处理逻辑
DispatcherServlet里doDispatch()就是springMVC的处理主要逻辑。因此肯定包含了拦截器的主要处理逻辑
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
try {
try {
//.......省略代码
//返回HandlerExecutionChain 其中包含了拦截器队列
mappedHandler = getHandler(processedRequest);
//调用拦截器PreHandle方法，若返回false不执行Controller逻辑，并不调用下面的PostHandle方法
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// 处理Controller层
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
applyDefaultViewName(processedRequest, mv);
//调用拦截器的PostHandle方法
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
//抛出异常后都会调用拦截器AfterCompletion方法
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
// Instead of postHandle and afterCompletion
if (mappedHandler != null) {
//若Controller方法为异步调用，则执行拦截器afterConcurrentHandlingStarted（只有AsyncHandlerInterceptor拦截器才有）
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
}
}
}2.2 获取拦截器
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
//返回HandlerExecutionChain 其中包含了拦截器队列
mappedHandler = getHandler(processedRequest);
}
//返回HandlerExecutionChain
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
return executionChain;
}
protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?
(HandlerExecutionChain) handler : new HandlerExecutionChain(handler));
//根据url和拦截器异常的配置url做对比，若符合则加入队列
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;
}
public boolean matches(String lookupPath, PathMatcher pathMatcher) {
PathMatcher pathMatcherToUse = (this.pathMatcher != null) ? this.pathMatcher : pathMatcher;
if (this.excludePatterns != null) {
for (String pattern : this.excludePatterns) {
if (pathMatcherToUse.match(pattern, lookupPath)) {
return false;
}
}
}
if (this.includePatterns == null) {
return true;
}
else {
for (String pattern : this.includePatterns) {
if (pathMatcherToUse.match(pattern, lookupPath)) {
return true;
}
}
return false;
}
}
上述的拦截器的信息，都来自与下面的配置文件
<!-- 拦截器链 -->
<mvc:interceptors>
<mvc:interceptor>
<!--拦截器mapping 符合的才会执行拦截器-->
<mvc:mapping path="/**"/>
<!--在拦截器mapping中除去下面的url -->
<mvc:exclude-mapping path="/transactional_test/*"/>
<!--执行的拦截器-->
<ref bean="apiInterceptor"/>
</mvc:interceptor>
</mvc:interceptors>
<bean id="apiInterceptor" class="com.lk.dome.interceptor.ApiInterceptor"/>2.3 处理拦截器
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];
//若返回false，则直接执行拦截器的triggerAfterCompletion方法
if (!interceptor.preHandle(request, response, this.handler)) {
triggerAfterCompletion(request, response, null);
//直接返回，在外层的doDispatch逻辑中不执行后面的逻辑
return false;
}
//记录成功执行的拦截器个数
this.interceptorIndex = i;
}
}
return true;
}
void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv) throws Exception {
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
//拦截器队列从后往前之心，顺序相反
for (int i = interceptors.length - 1; i >= 0; i--) {
HandlerInterceptor interceptor = interceptors[i];
interceptor.postHandle(request, response, this.handler, mv);
}
}
}
void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, Exception ex)
throws Exception {
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
//interceptorIndex为执行成功的拦截器标志
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);
}
}
}
}
//异步方法调用，拦截器必须属于AsyncHandlerInterceptor接口
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);
}
}
}
}
}