SpringMVC的处理器拦截器类似于Servlet开发中的过滤器Filter，用于对处理器进行于初期和后处理。开发者可以自己定义一些拦截器来实现特定的功能

过滤器与拦截器的区别：拦截器是AOP思想的具体应用不影响原来的功能但是可以实现拦截的效果

过滤器：

servlet规范中的一部分，任何java web工程都可以使用

在url-pattern中配置了/*之后，可以对所有要访问的资源进行拦截

<filter>
    <filter-name>encoding</filter-name>
    <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
    <init-param>
        <param-name>encoding</param-name>
        <param-value>utf-8</param-value>
    </init-param>
</filter>
<filter-mapping>
    <filter-name>encoding</filter-name>

    <url-pattern>/*</url-pattern>
</filter-mapping>

拦截器：

拦截器是SpringMVC框架自己有的，只有使用了SpringMVC框架的工程才能使用

拦截器只会拦截访问的控制器方法，如果访问的是jsp/html/css/image/js是不会进行拦截的（拦截器只会访问controller里面的请求并不会去拦截静态资源）

自己的总结：

数据独立性：SpringMVC方法间独立，独享request和response，而struts2虽然方法也是独立，但是所有的action变量是共享的，

拦截机制：SpringMVC 用的是独立的aop方式，struts2 有自己的interceptor机制所以struts2的配置文件要大于springMVC

自定义拦截器：

如果想要实现拦截器，就必须实现HandlerInterceptor接口

package com.kuang.interceptor;

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

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

public class MyInterceptor implements HandlerInterceptor {

    //在请求处理的方法之前执行
    //如果返回true执行下一个拦截器
    //如果返回false就不执行下一个拦截器
    public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o) throws Exception {
        System.out.println("------------处理前------------");
        return true;
        // return false 就拦截住 无法往下执行  穿透不了拦截器这一道墙
    }

    //在请求处理方法执行之后执行 拦截日志
    public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {
        System.out.println("------------处理后------------");
    }

    //在dispatcherServlet处理后执行,做清理工作.
    public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {
        System.out.println("------------清理------------");
    }
}

package com.kuang.controller;


import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/inter")
public class interceptor {


    @RequestMapping("/t1")
    public String test1(){
        System.out.println("t1");
        return "t1";
    }

}

案例:用户登陆，登陆成功跳转成功页面，如果不登陆就进不去成功页面，会强制跳转到登陆页面

拦截器代码：

package com.kuang.interceptor;

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

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

public class LoginInterceptor implements HandlerInterceptor {

    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws ServletException, IOException {
        // 如果是登陆页面则放行 请求路径里面只要有login就在login页面 放行
        System.out.println("uri: " + request.getRequestURI());
        if (request.getRequestURI().contains("login")) {
            return true;
        }

        HttpSession session = request.getSession();

        // 如果用户已登陆也放行 用户已登陆 session存在用户信息 放行
        if(session.getAttribute("user") != null) {
            return true;
        }

        // 用户没有登陆跳转到登陆页面 跳转到登陆页面
        request.getRequestDispatcher("/WEB-INF/jsp/login.jsp").forward(request, response);
        return false;
    }

    public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {

    }

    public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {

    }

}

后台代码：

package com.kuang.controller;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;

import javax.servlet.http.HttpSession;

@Controller
@RequestMapping("/user")
public class UserController {

    //跳转到登陆页面
    @RequestMapping("/jumplogin")
    public String jumpLogin() throws Exception {
        return "login";
    }

    //跳转到成功页面
    @RequestMapping("/jumpSuccess")
    public String jumpSuccess() throws Exception {
        return "success";
    }

    //登陆提交
    @RequestMapping("/login")
    public String login(HttpSession session, String username, String pwd) throws Exception {
        // 向session记录用户身份信息
        System.out.println("接收前端==="+username);
        session.setAttribute("user", username);
        return "success";
    }

    //退出登陆
    @RequestMapping("logout")
    public String logout(HttpSession session) throws Exception {
        // session 过期
        session.invalidate();
        return "login";
    }

}

SpringMVC配置文件配置代码：

<?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
       https://www.springframework.org/schema/context/spring-context.xsd
       http://www.springframework.org/schema/mvc
       https://www.springframework.org/schema/mvc/spring-mvc.xsd">


    <context:component-scan base-package="com.kuang.controller"/>


    <mvc:default-servlet-handler></mvc:default-servlet-handler>


    <mvc:annotation-driven>
        <mvc:message-converters register-defaults="true">
            <bean class="org.springframework.http.converter.StringHttpMessageConverter">
                <constructor-arg value="UTF-8"/>
            </bean>
            <bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
                <property name="objectMapper">
                    <bean class="org.springframework.http.converter.json.Jackson2ObjectMapperFactoryBean">
                        <property name="failOnEmptyBeans" value="false"/>
                    </bean>
                </property>
            </bean>
        </mvc:message-converters>
    </mvc:annotation-driven>

    <mvc:interceptors>

        <mvc:interceptor>
            <mvc:mapping path="/**"/>
                <bean class="com.kuang.interceptor.MyInterceptor"/>
        </mvc:interceptor>

        <mvc:interceptor>
            <mvc:mapping path="/user/**"/>
                <bean class="com.kuang.interceptor.LoginInterceptor"/>
        </mvc:interceptor>

    </mvc:interceptors>


    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver"
          id="internalResourceViewResolver">

        <property name="prefix" value="/WEB-INF/jsp/" />

        <property name="suffix" value=".jsp" />
    </bean>

</beans>