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;
 
import org.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 Tomcat 8080 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：