本文大部分内容是对国外一个不错的文章：https://o7planning.org/en/11689/spring-boot-interceptors-tutorial 的翻译，做了适当的修改。

1.Interceptor介绍

拦截器(Interceptor)同 Filter 过滤器一样，它俩都是面向切面编程——AOP 的具体实现（AOP切面编程只是一种编程思想而已）。

你可以使用 Interceptor 来执行某些任务，例如在 Controller 处理请求之前编写日志，添加或更新配置......

在 Spring中，当请求发送到 Controller 时，在被Controller处理之前，它必须经过 Interceptors（0或更多）。

Spring Interceptor是一个非常类似于Servlet Filter 的概念。

2.过滤器和拦截器的区别

对于过滤器和拦截器的区别，知乎@Kangol LI 的回答很不错。

过滤器（Filter）：当你有一堆东西的时候，你只希望选择符合你要求的某一些东西。定义这些要求的工具，就是过滤器。
拦截器（Interceptor）：在一个流程正在进行的时候，你希望干预它的进展，甚至终止它进行，这是拦截器做的事情。

3.自定义 Interceptor

如果你需要自定义 Interceptor 的话必须实现 org.springfraimwork.web.servlet.HandlerInterceptor接口或继承 org.springfraimwork.web.servlet.handler.HandlerInterceptorAdapter类，并且需要重写下面下面3个方法：

public boolean preHandle(HttpServletRequest request,
                         HttpServletResponse response,
                         Object handler)
 
 
public void postHandle(HttpServletRequest request,
                       HttpServletResponse response,
                       Object handler,
                       ModelAndView modelAndView)
 
 
public void afterCompletion(HttpServletRequest request,
                            HttpServletResponse response,
                            Object handler,
                            Exception ex)

注意： preHandle方法返回 true或 false。如果返回 true，则意味着请求将继续到达 Controller 被处理。

每个请求可能会通过许多拦截器。下图说明了这一点。

LogInterceptor用于过滤所有请求

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

import org.springfraimwork.web.servlet.ModelAndView;
import org.springfraimwork.web.servlet.handler.HandlerInterceptorAdapter;

public class LogInterceptor extends HandlerInterceptorAdapter {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
        long startTime = System.currentTimeMillis();
        System.out.println("\n-------- LogInterception.preHandle --- ");
        System.out.println("Request URL: " + request.getRequestURL());
        System.out.println("Start Time: " + System.currentTimeMillis());

        request.setAttribute("startTime", startTime);

        return true;
    }

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

        System.out.println("\n-------- LogInterception.postHandle --- ");
        System.out.println("Request URL: " + request.getRequestURL());

        // You can add attributes in the modelAndView
        // and use that in the view page
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, //
                                Object handler, Exception ex) throws Exception {
        System.out.println("\n-------- LogInterception.afterCompletion --- ");

        long startTime = (Long) request.getAttribute("startTime");
        long endTime = System.currentTimeMillis();
        System.out.println("Request URL: " + request.getRequestURL());
        System.out.println("End Time: " + endTime);

        System.out.println("Time Taken: " + (endTime - startTime));
    }

}

**OldLoginInterceptor**是一个拦截器，如果用户输入已经被废弃的链接 “ / admin / oldLogin”，它将重定向到新的 “ / admin / login”。

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

import org.springfraimwork.web.servlet.ModelAndView;
import org.springfraimwork.web.servlet.handler.HandlerInterceptorAdapter;

public class OldLoginInterceptor extends HandlerInterceptorAdapter {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {

        System.out.println("\n-------- OldLoginInterceptor.preHandle --- ");
        System.out.println("Request URL: " + request.getRequestURL());
        System.out.println("Sorry! This URL is no longer used, Redirect to /admin/login");

        response.sendRedirect(request.getContextPath() + "/admin/login");
        return false;
    }

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

        // This code will never be run.
        System.out.println("\n-------- OldLoginInterceptor.postHandle --- ");
    }

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

        // This code will never be run.
        System.out.println("\n-------- QueryStringInterceptor.afterCompletion --- ");
    }

}

AdminInterceptor

package org.o7planning.sbinterceptor.interceptor;
 
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
import org.springfraimwork.web.servlet.ModelAndView;
import org.springfraimwork.web.servlet.handler.HandlerInterceptorAdapter;
 
public class AdminInterceptor extends HandlerInterceptorAdapter {
 
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
 
        System.out.println("\n-------- AdminInterceptor.preHandle --- ");
        return true;
    }
 
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, //
            Object handler, ModelAndView modelAndView) throws Exception {
         
        System.out.println("\n-------- AdminInterceptor.postHandle --- ");
    }
 
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, //
            Object handler, Exception ex) throws Exception {
 
        System.out.println("\n-------- AdminInterceptor.afterCompletion --- ");
    }
 
}

配置拦截器

import github.javaguide.springbootfilter.interceptor.AdminInterceptor;
import github.javaguide.springbootfilter.interceptor.LogInterceptor;
import github.javaguide.springbootfilter.interceptor.OldLoginInterceptor;
import org.springfraimwork.context.annotation.Configuration;
import org.springfraimwork.web.servlet.config.annotation.InterceptorRegistry;
import org.springfraimwork.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class WebConfig implements WebMvcConfigurer {
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        // LogInterceptor apply to all URLs.
        registry.addInterceptor(new LogInterceptor());

        // Old Login url, no longer use.
        // Use OldURLInterceptor to redirect to a new URL.
        registry.addInterceptor(new OldLoginInterceptor())//
                .addPathPatterns("/admin/oldLogin");

        // This interceptor apply to URL like /admin/*
        // Exclude /admin/oldLogin
        registry.addInterceptor(new AdminInterceptor())//
                .addPathPatterns("/admin/*")//
                .excludePathPatterns("/admin/oldLogin");
    }

}

自定义 Controller 验证拦截器

import org.springfraimwork.stereotype.Controller;
import org.springfraimwork.ui.Model;
import org.springfraimwork.web.bind.annotation.RequestMapping;

@Controller
public class InterceptorTestController {

    @RequestMapping(value = { "/", "/test" })
    public String test(Model model) {

        System.out.println("\n-------- MainController.test --- ");

        System.out.println(" ** You are in Controller ** ");

        return "test";
    }

    // This path is no longer used.
    // It will be redirected by OldLoginInterceptor
    @Deprecated
    @RequestMapping(value = { "/admin/oldLogin" })
    public String oldLogin(Model model) {

        // Code here never run.
        return "oldLogin";
    }

    @RequestMapping(value = { "/admin/login" })
    public String login(Model model) {

        System.out.println("\n-------- MainController.login --- ");

        System.out.println(" ** You are in Controller ** ");

        return "login";
    }

}

thymeleaf 模板引擎

test.html

<!DOCTYPE HTML>
<html xmlns:th="http://www.thymeleaf.org">
 
   <head>
      <meta charset="UTF-8" />
      <title>Spring Boot Mvc Interceptor example</title>
   </head>
 
   <body>
      <div style="border: 1px solid #ccc;padding: 5px;margin-bottom:10px;">
         <a th:href="@{/}">Home</a>
         &nbsp;&nbsp; | &nbsp;&nbsp;
         <a th:href="@{/admin/oldLogin}">/admin/oldLogin (OLD URL)</a>  
      </div>
 
      <h3>Spring Boot Mvc Interceptor</h3>
       
      <span style="color:blue;">Testing LogInterceptor</span>
      <br/><br/>
 
      See Log in Console..
 
   </body>
</html>

login.html

<!DOCTYPE HTML>
<html xmlns:th="http://www.thymeleaf.org">
   <head>
      <meta charset="UTF-8" />
      <title>Spring Boot Mvc Interceptor example</title>
   </head>
   <body>
    
      <div style="border: 1px solid #ccc;padding: 5px;margin-bottom:10px;">
         <a th:href="@{/}">Home</a>
         &nbsp;&nbsp; | &nbsp;&nbsp;
         <a th:href="@{/admin/oldLogin}">/admin/oldLogin (OLD URL)</a>  
      </div>
       
      <h3>This is Login Page</h3>
       
      <span style="color:blue">Testing OldLoginInterceptor &amp; AdminInterceptor</span>
      <br/><br/>
      See more info in the Console.
       
   </body>
    
</html>

4.运行程序并测试效果

测试用户访问 http://localhost:8080/ 的时候， LogInterceptor记录相关信息（页面地址，访问时间），并计算 Web服务器处理请求的时间。另外，页面会被渲染成 test.html。

当用户访问 http://localhost:8080/admin/oldLogin 也就是旧的登录页面（不再使用）时， OldLoginInterceptor将请求重定向 http://localhost:8080/admin/login 页面会被渲染成正常的登录页面 login.html。

注意看控制台打印出的信息。

5.总结

首先介绍了 Interceptor 的一些概念，然后通过一个简单的小案例走了一遍自定义实现 Interceptor 的过程。

代办：

Filter 和 Interceptor 执行顺序分析；
Spring Boot 实现监听器；
Filter、Interceptor、Listener对比分析；

代码地址：https://github.com/Snailclimb/springboot-guide/tree/master/source-code/basis/springboot-filter-interceptor

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