SpringBoot拦截器详解

您可以在 Spring Boot 中使用 Interceptor 在以下情况下执行操作 

在向控制器发送请求之前

在向客户端发送响应之前

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

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

以下是您在使用拦截器时应该了解的三种方法 

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 - 用于在向客户端发送响应之前执行操作。

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WebMvcConfigurerAdapter向InterceptorRegistry注册此拦截器，如下所示

@Component
public class ProductServiceInterceptorAppConfig extends WebMvcConfigurerAdapter {
   @Autowired
   ProductServiceInterceptor productServiceInterceptor;
   @Override
   public void addInterceptors(InterceptorRegistry registry) {
      registry.addInterceptor(productServiceInterceptor);
   }
}

在下面给出的示例中，我们将点击 GET products API，它提供如下所示的输出 

拦截器类 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");
   }
}

下面给出了将拦截器注册到拦截器注册表的应用程序配置类文件的代码

 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.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;
   }
}

主 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 构建的代码 - pom.xml显示在这里

<?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的代码如下所示

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 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”后，可以在目标目录下找到JAR文件。

对于 Gradle，使用如下所示的命令

gradle clean build

“BUILD SUCCESSFUL”后，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

现在在 POSTMAN 应用程序中点击以下 URL，您可以看到如下所示的输出 

获取 API：http://localhost:8080/products

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

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