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Spring Boot - 拦截器

您可以在以下情况下使用Spring Boot中的拦截器(Interceptor)来执行操作-

在将请求发送到控制器之前
在将响应发送给客户端之前

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，并且该类应实现 HandlerInterceptor 接口。

以下是使用拦截器时应了解的三种方法-

preHandle() - 用于在将请求发送到控制器之前执行操作，需要返回true。
postHandle() - 用于在将响应发送到客户端之前执行操作。
afterCompletion() - 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，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，无涯教程将使用GET产品API，该产品的输出如下-

下面给出了Interceptor类ProductServiceInterceptor.java的代码-

package com.learnfk.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.learnfk.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.learnfk.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.learnfk.demo.exception.ProductNotfoundException;
import com.learnfk.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.learnfk.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;
   }
}

下面给出了主要的Spring Boot应用程序类文件 DemoApplication.java 的代码-

package com.learnfk.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 显示在此处-

<?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.learnfk</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>

这里显示了Gradle Build build.gradle 的代码-

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.learnfk'
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')
}