Spring Boot - 拦截器

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您可以在 Spring Boot 中使用拦截器在以下情况下执行操作：

  • 在将请求发送到控制器之前

  • 在将响应发送到客户端之前

例如，您可以在将请求发送到控制器之前使用拦截器添加请求头，并在将响应发送到客户端之前添加响应头。

要使用拦截器，您需要创建一个支持它的@Component类，并且它应该实现HandlerInterceptor接口。

以下是在处理拦截器时您应该了解的三个方法：

  • preHandle()方法 - 用于在将请求发送到控制器之前执行操作。此方法应返回 true 以将响应返回给客户端。

  • postHandle()方法 - 用于在将响应发送到客户端之前执行操作。

  • afterCompletion()方法 - 用于在完成请求和响应后执行操作。

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 {}
}

您必须使用WebMvcConfigurer通过InterceptorRegistry注册此拦截器，如下所示：

@Component
public class ProductServiceInterceptorAppConfig implements WebMvcConfigurer {
   @Autowired
   ProductServiceInterceptor productServiceInterceptor;

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

在下面给出的示例中，我们将访问 GET products API，它会给出如下输出：

拦截器类 ProductServiceInterceptor.java 的代码如下：

ProductServiceInterceptor.java

package com.tutorialspoint.demo.interceptor;

import jakarta.servlet.http.HttpServletRequest;
import jakarta.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");
   }
}

将拦截器注册到拦截器注册表中的应用程序配置类文件 ProductServiceInterceptorAppConfig.java 的代码如下：

ProductServiceInterceptorAppConfig.java

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.WebMvcConfigurer;

@Component
public class ProductServiceInterceptorAppConfig implements WebMvcConfigurer {
   @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：

ProductServiceController.java

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

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);      
   }
   @GetMapping(value = "/products")
   public ResponseEntity<Object> getProduct() {
      return new ResponseEntity<>(productRepo.values(), HttpStatus.OK);
   }
}

Product.java 的 POJO 类代码如下：

Product.java

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 应用程序类文件DemoApplication.java的代码如下：

DemoApplication.java

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 – pom.xml的代码如下所示：

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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
   <modelVersion>4.0.0</modelVersion>
   <parent>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-parent</artifactId>
      <version>3.3.3</version>
      <relativePath/> <!-- lookup parent from repository -->
   </parent>
   <groupId>com.tutorialspoint</groupId>
   <artifactId>demo</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <name>demo</name>
   <description>Demo project for Spring Boot</description>
   <url/>
   <licenses>
      <license/>
   </licenses>
   <developers>
      <developer/>
   </developers>
   <scm>
      <connection/>
      <developerConnection/>
      <tag/>
      <url/>
   </scm>
   <properties>
      <java.version>21</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build.gradle的代码如下所示：

buildscript {
   ext {
      springBootVersion = '3.3.3'
   }
   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 = 21

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，请使用以下命令：

mvn clean install

“BUILD SUCCESS”之后，您可以在 target 目录下找到 JAR 文件。

对于 Gradle，请使用以下命令：

gradle clean build

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

您可以使用以下命令运行 JAR 文件：

java –jar <JARFILE>

现在，应用程序已在 Tomcat 端口 8080 上启动，如下所示：

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/

[32m :: Spring Boot :: [39m              [2m (v3.3.3)[0;39m

[2024-09-05T12:09:13Z] [org.springframework.boot.StartupInfoLogger] [main] [50] [INFO ] Starting DemoApplication using Java 21.0.3 with PID 2120 (E:\Dev\demo\target\classes started by Tutorialspoint in E:\Dev\demo)
[2024-09-05T12:09:13Z] [org.springframework.boot.SpringApplication] [main] [654] [INFO ] No active profile set, falling back to 1 default profile: "default"
[2024-09-05T12:09:14Z] [org.springframework.boot.web.embedded.tomcat.TomcatWebServer] [main] [111] [INFO ] Tomcat initialized with port 8080 (http)
[2024-09-05T12:09:14Z] [org.apache.juli.logging.DirectJDKLog] [main] [173] [INFO ] Initializing ProtocolHandler ["http-nio-8080"]
[2024-09-05T12:09:14Z] [org.apache.juli.logging.DirectJDKLog] [main] [173] [INFO ] Starting service [Tomcat]
[2024-09-05T12:09:14Z] [org.apache.juli.logging.DirectJDKLog] [main] [173] [INFO ] Starting Servlet engine: [Apache Tomcat/10.1.28]
[2024-09-05T12:09:14Z] [org.apache.juli.logging.DirectJDKLog] [main] [173] [INFO ] Initializing Spring embedded WebApplicationContext
[2024-09-05T12:09:14Z] [org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext] [main] [296] [INFO ] Root WebApplicationContext: initialization completed in 1072 ms
[2024-09-05T12:09:14Z] [org.apache.juli.logging.DirectJDKLog] [main] [173] [INFO ] Starting ProtocolHandler ["http-nio-8080"]
[2024-09-05T12:09:14Z] [org.springframework.boot.web.embedded.tomcat.TomcatWebServer] [main] [243] [INFO ] Tomcat started on port 8080 (http) with context path '/'
[2024-09-05T12:09:14Z] [org.springframework.boot.StartupInfoLogger] [main] [56] [INFO ] Started DemoApplication in 1.996 seconds (process running for 4.263)

现在在 POSTMAN 应用程序中访问以下 URL，您将看到如下输出：

GET API：https://127.0.0.1:8080/products

POSTMAN Application Get API URL

在控制台窗口中，您可以看到在拦截器中添加的 System.out.println 语句，如下面的屏幕截图所示：

Pre Handle method is Calling
Post Handle method is Calling
Request and Response is completed
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