（021）Spring Boot之拦截器HandlerInterceptor

　　 拦截器的使用步骤：

　　第一步，实现HandlerInterceptor接口，该接口有三个方法preHandle 、postHandle 、afterCompletion 

 　　（1）preHandle在controller执行之前调用

 　　（2）postHandle在controller执行之后，页面渲染之前调用

 　　（3）afterCompletion在页面渲染之后调用，一般用于资源清理操作

　　第二步，继承WebMvcConfigurationSupport或者实现WebMvcConfigurer，重写他们的addInterceptors方法。把上一步的拦截器加进去。

　　pom.xml

<?xml version="1.0" encoding="UTF-8"?>

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.edu.spring</groupId>
    <artifactId>springboot_web</artifactId>
    <version>1.0.0</version>

    <name>springboot_web</name>
    <!-- FIXME change it to the project's website -->
    <url>http://www.example.com</url>
    <parent> 
        <groupId>org.springframework.boot</groupId> 
        <artifactId>spring-boot-starter-parent</artifactId> 
        <version>2.0.4.RELEASE</version> 
    </parent>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
    </dependencies>

</project>

　　LogHandlerInterceptor.java

package com.edu.spring.springboot;

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

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

public class LogHandlerInterceptor implements HandlerInterceptor {

    
    
    @Override
    public boolean preHandle(HttpServletRequest request,
            HttpServletResponse response, Object handler) throws Exception {
        System.out.println("====================preHandle================="+handler.getClass().getName());
        return true;
    }
    
    @Override
    public void postHandle(HttpServletRequest request,
            HttpServletResponse response, Object handler,
            ModelAndView modelAndView) throws Exception {
        
        System.out.println("==================postHandle==================="+handler.getClass().getName());
        
    }
    
    @Override
    public void afterCompletion(HttpServletRequest request,
            HttpServletResponse response, Object handler, Exception ex)
            throws Exception {
        System.out.println("==================afterCompletion==================="+handler.getClass().getName());

    }
    
}

　　MyWebMvcConfigurationSupport.java

package com.edu.spring.springboot;

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport;

@Configuration
public class MyWebMvcConfigurationSupport extends WebMvcConfigurationSupport{

    @Override
    protected void addInterceptors(InterceptorRegistry registry) {
        // TODO Auto-generated method stub
        registry.addInterceptor(new LogHandlerInterceptor());
    }
}

　　或者MyWebMvcConfigurer.java

package com.edu.spring.springboot;

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class MyWebMvcConfigurer implements WebMvcConfigurer  {

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        // TODO Auto-generated method stub
        registry.addInterceptor(new LogHandlerInterceptor());
    }
}

　　UserController.java

package com.edu.spring.springboot;

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

@RestController
public class UserController {

    @RequestMapping("/user/home")
    public String home(){
        System.out.println("============home=============");
        return "user home";
    }
}

　　App.java

package com.edu.spring.springboot;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class App 
{
    public static void main(String[] args) {
         SpringApplication.run(App.class, args);
    }
}

　　浏览器输入：http://127.0.0.1:8080/user/home ，运行结果如下：