interceptor（拦截器）
拦截器，顾名思义，他的作用就是拦截，这个要和过滤器区分开，过滤器依赖serverlet容器，获取request和response处理，是基于函数回调，简单说就是“去取你想取的”，拦截器是通过java反射机制，动态代理来拦截web请求，是“拒你想拒绝的”，他只拦截web请求，但不拦截静态资源，Struts2里面就是将拦截器串联，实现对请求的处理，下面以spring 的拦截器为例，写个demo
/**
* @author wtzhouc@gmail.com
* @date 2019-04-13 14:50
*/
@Component
public class MyInterceptor implements HandlerInterceptor {
@Override
public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object hanlder) {
out.println("拦截器.preHandle 开始执行。。。");
out.println(hanlder.getClass().getSimpleName());
out.println(((HandlerMethod) hanlder).getBean().getClass().getName());
httpServletRequest.setAttribute("start", currentTimeMillis());
return true;
}
@Override
public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object hanlder, ModelAndView modelAndView) {
out.println("拦截器.postHandle 开始执行。。。");
long start = (long) httpServletRequest.getAttribute("start");
out.println("postHandle执行时间为：" + (currentTimeMillis() - start));
}
@Override
public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object hanlder, Exception e) {
//会打印两次 spring里面的basic error 也会被拦截
out.println("拦截器.afterCompletion 开始执行。。。");
long start = (long) httpServletRequest.getAttribute("start");
out.println("afterCompletion执行时间为：" + (currentTimeMillis() - start));
out.println("\n ex is :" + e+"\n");
}
}
