Spring MVC 拦截器（HandlerIntercepto

Spring MVC的处理器拦截器（HandlerInterceptor）类似于Servlet 规范中的过滤器Filter，用于对处理器进行预处理和后处理。

HandlerInterceptor 接口

package org.springframework.web.servlet;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.web.method.HandlerMethod;

public interface HandlerInterceptor {

    /**
     * 预处理回调方法
     * true表示继续流程, false表示流程中断
     */
    boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception;

    /**
     * 后处理回调方法，实现处理器的后处理（但在渲染视图之前），此时可以通过modelAndView对模型数据进行处理或对视图进行处理
     */
    void postHandle(
            HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView)
            throws Exception;

    /**
     * 整个请求处理完毕回调方法，即在视图渲染完毕时回调
     */
    void afterCompletion(
            HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
            throws Exception;

}

Spring MVC 提供了一个HandlerInterceptorAdapter 适配器类，让我们可以有选择的去实现感兴趣的方法，如下：

package org.springframework.web.servlet.handler;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.AsyncHandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

/**
 * Abstract adapter class for the {@link AsyncHandlerInterceptor} interface,
 * for simplified implementation of pre-only/post-only interceptors.
 *
 * @author Juergen Hoeller
 * @since 05.12.2003
 */
public abstract class HandlerInterceptorAdapter implements AsyncHandlerInterceptor {

    /**
     * This implementation always returns {@code true}.
     */
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {

        return true;
    }

    /**
     * This implementation is empty.
     */
    @Override
    public void postHandle(
            HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView)
            throws Exception {
    }

    /**
     * This implementation is empty.
     */
    @Override
    public void afterCompletion(
            HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
            throws Exception {
    }

    /**
     * This implementation is empty.
     */
    @Override
    public void afterConcurrentHandlingStarted(
            HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
    }

}

跟Netty4.1中的 ChannelInboundHandler和 ChannelInboundHandlerAdapter有异曲同工之妙。

使用

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
     http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
     http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd">

    <mvc:annotation-driven />
    <context:component-scan base-package="com.bytebeats.springmvc.ch5.controller" >
        <context:include-filter type="annotation" expression="org.springframework.stereotype.Controller" />
    </context:component-scan>

    <mvc:interceptors>
        <mvc:interceptor>
            <mvc:mapping path="/**" />
            <bean class="com.bytebeats.springmvc.ch5.controller.interceptor.LogInterceptor" />
        </mvc:interceptor>
        <mvc:interceptor>
            <mvc:mapping path="/api/**" />
            <mvc:exclude-mapping path="/api/auth/login" />
            <mvc:exclude-mapping path="/api/auth/register" />
            <bean class="com.bytebeats.springmvc.ch5.controller.interceptor.AuthInterceptor" />
        </mvc:interceptor>
    </mvc:interceptors>

</beans>

LogInterceptor

import java.util.Set;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;


public class LogInterceptor implements HandlerInterceptor{

    private Logger logger = LoggerFactory.getLogger(LogInterceptor.class);
    
    @Override
    public boolean preHandle(HttpServletRequest request,
            HttpServletResponse response, Object handler) throws Exception {
        
        if(condition){
            return false;
        }
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request,
            HttpServletResponse response, Object handler,
            ModelAndView modelAndView) throws Exception {
        
    }

    @Override
    public void afterCompletion(HttpServletRequest request,
            HttpServletResponse response, Object handler, Exception ex)
            throws Exception {
        
    }

}

应用场景

• 日志记录：记录请求信息的日志，以便进行信息监控、信息统计、计算PV，trace跟踪 等。
• 权限检查：如登录检测，进入处理器检测检测是否登录，如果没有直接返回到登录页面；
• 性能监控：有时候系统在某段时间莫名其妙的慢，可以通过拦截器在进入处理器之前记录开始时间，在处理完后记；

关于 HandlerInterceptor 内部实现原理，下一篇文章中会详细介绍。