Spring Boot 简明教程

Spring Boot - Interceptor

你可以在 Spring Boot 中使用 Interceptor 在下列情况中执行操作 −

  1. 在向控制器发送请求之前

  2. 在向客户端发送响应之前

例如，你可以在向控制器发送请求之前使用拦截器添加请求头，并在向客户端发送响应之前添加响应头。

要使用拦截器，你需要创建支持它的 @Component 类，并实现 HandlerInterceptor 接口。

以下是使用拦截器时你需要了解的三种方法 −

  1. preHandle() 方法 − 该方法用于在向控制器发送请求之前执行操作。该方法应返回 true 以将响应返回给客户端。

  2. postHandle() 方法 − 该方法用于在向客户端发送响应之前执行操作。

  3. afterCompletion() 方法 − 该方法用于在完成请求和响应之后执行操作。

观察以下代码以更好地理解 −

@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 {}
}

你需要通过使用 WebMvcConfigurerAdapter 将此 Interceptor 注册到 InterceptorRegistry ，如下所示 −

@Component
public class ProductServiceInterceptorAppConfig extends WebMvcConfigurerAdapter {
   @Autowired
   ProductServiceInterceptor productServiceInterceptor;

   @Override
   public void addInterceptors(InterceptorRegistry registry) {
      registry.addInterceptor(productServiceInterceptor);
   }
}

在下面的示例中，我们将触及 GET products API，其输出如下所示 −

Interceptor 类 ProductServiceInterceptor.java 的代码如下 −

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");
   }
}

注册 Interceptor 的应用程序配置类文件的代码，InterceptorRegistry – ProductServiceInterceptorAppConfig.java 如下所示 −

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);
   }
}

控制器类文件 ProductServiceController.java 的代码如下 −

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);
   }
}

Product.java 的 POJO 类文件的代码如下 −

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;
   }
}

Spring Boot 应用程序类文件 DemoApplication.java 的代码如下 −

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 构建代码 – pom.xml 如下所示 −

<?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 构建代码 build.gradle 如下所示 −

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')
}

您可以创建一个可执行的 JAR 文件，并使用以下 Maven 或 Gradle 命令运行 Spring Boot 应用程序。

对于 Maven，使用如下所示的命令：

mvn clean install

“BUILD SUCCESS”之后，您可以在目标目录中找到 JAR 文件。

对于 Gradle，像下面这样使用命令 -

gradle clean build

“BUILD SUCCESSFUL”之后，您可以在 build/libs 目录中找到 JAR 文件。

你可以使用以下命令运行 JAR 文件 −

java –jar <JARFILE>

现在，应用程序在 Tomcat 端口 8080 上启动，如下所示 -

started application on tomcat port 8080

现在在 POSTMAN 应用程序中点击下面的 URL，您会看到像下面显示的输出−

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

postman application get api url

在控制台窗口中，您会看到在拦截器中添加的 System.out.println 语句，如下面给出的屏幕截图所示−

interceptor output console window