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  Spring Boot 拦截器

  • 拦截器

    在以下情况下，可以使用Spring Boot中的Interceptor(拦截器)来执行操作：
    • 在将请求发送到控制器之前(拦截请求)
    • 在将响应发送给客户端之前(拦截响应)
    例如，您可以使用拦截器在将请求发送到控制器之前添加请求标头，并在将响应发送到客户端之前添加响应标头。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。
    以下是使用拦截器时应了解的三种方法-
    • 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 - 用于在将响应发送到客户端之前执行操作。
    • afterCompletion()方法 - 用于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 {}
}
    您将必须使用WebMvcConfigurerAdapter向InterceptorRegistry注册此拦截器r，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，我们将使用GET products API，该产品的输出如下 -
    下面给出了Interceptor类ProductServiceInterceptor.java的代码- 
    
package com.jc2182.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");
   }
}
    下面提供了用于将拦截器注册到拦截器注册表中的Application Configuration类文件的代码– ProductServiceInterceptorAppConfig.java 
    
package com.jc2182.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的代码如下所示- 
    
package com.jc2182.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.jc2182.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);
   }
}
    下面给出了Product.java的POJO类的代码- 
    
package com.jc2182.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;
   }
}
    下面给出了Spring Boot应用程序类文件DemoApplication.java的main方法代码- 
    
package com.jc2182.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 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>2.3.0.BUILD-SNAPSHOT</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.jc2182</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <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>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

    <repositories>
        <repository>
            <id>spring-milestones</id>
            <name>Spring Milestones</name>
            <url>https://repo.spring.io/milestone</url>
        </repository>
        <repository>
            <id>spring-snapshots</id>
            <name>Spring Snapshots</name>
            <url>https://repo.spring.io/snapshot</url>
            <snapshots>
                <enabled>true</enabled>
            </snapshots>
        </repository>
    </repositories>
    <pluginRepositories>
        <pluginRepository>
            <id>spring-milestones</id>
            <name>Spring Milestones</name>
            <url>https://repo.spring.io/milestone</url>
        </pluginRepository>
        <pluginRepository>
            <id>spring-snapshots</id>
            <name>Spring Snapshots</name>
            <url>https://repo.spring.io/snapshot</url>
            <snapshots>
                <enabled>true</enabled>
            </snapshots>
        </pluginRepository>
    </pluginRepositories>

</project>
    下面给出了Gradle Build – build.gradle的代码- 
    
plugins {
    id 'org.springframework.boot' version '2.3.0.BUILD-SNAPSHOT'
    id 'io.spring.dependency-management' version '1.0.9.RELEASE'
    id 'java'
}

group = 'com.jc2182'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '1.8'

repositories {
    mavenCentral()
    maven { url 'https://repo.spring.io/milestone' }
    maven { url 'https://repo.spring.io/snapshot' }
}

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-web'
    testImplementation('org.springframework.boot:spring-boot-starter-test') {
        exclude group: 'org.junit.vintage', module: 'junit-vintage-engine'
    }
}

test {
    useJUnitPlatform()
}
    RESTFul Web 服务参考>>>
    您可以创建一个可执行的JAR文件，并使用Maven或Gradle命令运行Spring Boot应用程序-
    对于Maven，您可以使用以下命令- 
    
mvn clean install
    在“BUILD SUCCESS”之后，您可以在target目录下找到JAR文件。
    对于Gradle，您可以使用以下命令- 
    
gradle clean build
    在“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>
    在Tomcat端口8080上启动应用程序
    现在在POSTMAN应用程序中请求URL，您可以看到如下所示的输出-
    PUT URL：http://localhost:8080/products
    springboot excpt
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