Spring Boot 教程： 拦截器

【注】本文译自：https://www.tutorialspoint.com/spring_boot/spring_boot_interceptor.htm

        在以下两种情况下，可以在 Spring Boot 中使用拦截器来执行操作：

发送请求到控制器之前

发送响应到客户端之前

       譬如，可以使用拦截器在发送请求到控制器之前添加请求头，并在发送响应到客户端之前添加响应头。

       要用拦截器，你需要创建 @Component 类，并且要实现 HandlerInterceptor 接口。

       下面是使用拦截器要知道的三个方法：

preHandle() 方法：用于在发送请求到控制器之前执行操作。这个方法应当返回 true 以响应客户端。

postHandle() 方法：用于在发送响应到客户端之前执行操作。

afterCompletion() 方法： 用于在请求和响应完成之后执行操作。

       观察以下代码以加深理解：

@Component

public class ProductServiceInterceptor implements HandlerInterceptor {

   @Override

   public boolean preHandle(

      HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {

      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 exception) throws Exception {}

}

       还要通过 WebMvcConfigurerAdapter 用 InterceptorRegistry 注册这个拦截器：

@Component

public class ProductServiceInterceptorAppConfig extends WebMvcConfigurerAdapter {

   @Autowired

   ProductServiceInterceptor productServiceInterceptor;

   @Override

   public void addInterceptors(InterceptorRegistry registry) {

      registry.addInterceptor(productServiceInterceptor);

   }

}

       在下面给出的示例中，我们将要使用后面给出的 GET products API：

       Interceptor 类文件 ProductServiceInterceptor.java 如下所示：

package com.tutorialspoint.demo.interceptor;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

importorg.springframework.stereotype.Component;

import org.springframework.web.servlet.HandlerInterceptor;

import org.springframework.web.servlet.ModelAndView;

@Component

public class ProductServiceInterceptor implements HandlerInterceptor {

   @Override

   public boolean preHandle

      (HttpServletRequest request, HttpServletResponse response, Object handler)

      throws Exception {

      System.out.println("Pre Handle method is Calling");

      return true;

   }

   @Override

   public void postHandle(HttpServletRequest request, HttpServletResponse response,

      Object handler, ModelAndView modelAndView) throws Exception {

      System.out.println("Post Handle method is Calling");

   }

   @Override

   public void afterCompletion

      (HttpServletRequest request, HttpServletResponse response, Object

      handler, Exception exception) throws Exception {

      System.out.println("Request and Response is completed");

   }

}

        Application Configuration 类文件把拦截器注册到 Interceptor Registry中，ProductServiceInterceptorAppConfig.java 文件如下：

package com.tutorialspoint.demo.interceptor;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.stereotype.Component;

import org.springframework.web.servlet.config.annotation.InterceptorRegistry;

import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;

@Component

public class ProductServiceInterceptorAppConfig extends WebMvcConfigurerAdapter {

   @Autowired

   ProductServiceInterceptor productServiceInterceptor;

   @Override

   public void addInterceptors(InterceptorRegistry registry) {

      registry.addInterceptor(productServiceInterceptor);

   }

}

     Controller 类文件 ProductServiceController.java 如下：

package com.tutorialspoint.demo.controller;

import java.util.HashMap;

import java.util.Map;

import org.springframework.http.HttpStatus;

import org.springframework.http.ResponseEntity;

import org.springframework.web.bind.annotation.PathVariable;

import org.springframework.web.bind.annotation.RequestBody;

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

import org.springframework.web.bind.annotation.RequestMethod;

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

import com.tutorialspoint.demo.exception.ProductNotfoundException;

import com.tutorialspoint.demo.model.Product;

@RestController

public class ProductServiceController {

   private static Map<String, Product> productRepo = new HashMap<>();   

   static {      

      Product honey = new Product();

      honey.setId("1");

      honey.setName("Honey");

      productRepo.put(honey.getId(), honey);      

      Product almond = new Product();

      almond.setId("2");

      almond.setName("Almond");

      productRepo.put(almond.getId(), almond);      

   }

   @RequestMapping(value = "/products")

   public ResponseEntity<Object> getProduct() {

      return new ResponseEntity<>(productRepo.values(), HttpStatus.OK);

   }

}

       POJO 类文件 Product.java 如下：

package com.tutorialspoint.demo.model;

public class Product {

   private String id;

   private String name;

   public String getId() {

      return id;

   }

   public void setId(String id) {

      this.id = id;

   }

   public String getName() {

      return name;

   }

   public void setName(String name) {

      this.name = name;

   }

}

       主 Spring Boot 应用类文件 DemoApplication.java 如下所示：

package com.tutorialspoint.demo;

import org.springframework.boot.SpringApplication;

import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication

public class DemoApplication {

   public static void main(String[] args) {

      SpringApplication.run(DemoApplication.class, args);   

   }

}

       Maven build – pom.xml 文件在此：

<?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.tutorialspoint</groupId>

   <artifactId>demo</artifactId>

   <version>0.0.1-SNAPSHOT</version>

   <packaging>jar</packaging>

   <name>demo</name>

   <description>Demo project for Spring Boot</description>

   <parent>

      <groupId>org.springframework.boot</groupId>

      <artifactId>spring-boot-starter-parent</artifactId>

      <version>1.5.8.RELEASE</version>

      <relativePath/>

   </parent>

   <properties>

      <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>

      <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>

      <java.version>1.8</java.version>

   </properties>

   <dependencies>

      <dependency>

         <groupId>org.springframework.boot</groupId>

         <artifactId>spring-boot-starter-web</artifactId>

      </dependency>

      <dependency>

         <groupId>org.springframework.boot</groupId>

         <artifactId>spring-boot-starter-test</artifactId>

         <scope>test</scope>

      </dependency>

   </dependencies>

   <build>

      <plugins>

         <plugin>

            <groupId>org.springframework.boot</groupId>

            <artifactId>spring-boot-maven-plugin</artifactId>

         </plugin>

      </plugins>

   </build>

</project>

     Gradle Build build.gradle 文件在此：

buildscript {

   ext {

      springBootVersion = '1.5.8.RELEASE'

   }

   repositories {

      mavenCentral()

   }

   dependencies {

      classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")

   }

}

apply plugin: 'java'

apply plugin: 'eclipse'

apply plugin: 'org.springframework.boot'

group = 'com.tutorialspoint'

version = '0.0.1-SNAPSHOT'

sourceCompatibility = 1.8

repositories {

   mavenCentral()

}

dependencies {

   compile('org.springframework.boot:spring-boot-starter-web')

   testCompile('org.springframework.boot:spring-boot-starter-test')

}

      你可以使用下面的 Maven 或 Gradle 命令创建可执行的 JAR 文件，运行 Spring Boot 应用：

       对于 Maven，使用以下命令：

mvn clean install

       在 “BUILD SUCCESS” 之后，你可以在 target 目录下找到 JAR 文件：

      对于 Gradle，使用以下命令：

gradle clean build

       在 “BUILD SUCCESSFUL” 之后，你可以在build/libs 目录下找到 JAR 文件：

       可以使用以下命令运行 JAR 文件：

java –jar <JARFILE>

       此时，应用已经在 Tomcat8080 端口启动了，如下所示：

       在 POSTMAN 应用中单击以下 URL，你可以看到下面的结果：

GET API: http://localhost:8080/products

       在控制台窗口，你可以看到加在拦截器中的 System.out.println 打印出来的结果，截屏如下：