Spring Boot 拦截器

在以下情况下可以使用 Spring Boot 中的 Interceptor 进行操作：

• 在向控制器发送请求之前；
• 在向客户端发送响应之前

例如，我们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，需要创建支持它的 @Component 类，并且它应该实现 HandlerInterceptor 接口。

以下是我们在使用拦截器时应该了解的三种方法

• preHandle() 方法 - 这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。

查看以下代码来更好地理解

@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 {}
}

我们必须使用 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，我们将使用 GET products API，它给出如下所示的输出

下面给出拦截器类 ProductServiceInterceptor.java 的代码

package com.study.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;

/**
 * @author jiyik.com
 */
@Component
public class ProductServiceInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle (HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {

        System.out.println("Pre Handle 方法正在调用");
        return true;
    }
    @Override
    public void postHandle (HttpServletRequest request, HttpServletResponse response,
                           Object handler, ModelAndView modelAndView) throws Exception {

        System.out.println("Post Handle 方法正在调用");
    }
    @Override
    public void afterCompletion (HttpServletRequest request, HttpServletResponse response, Object
                    handler, Exception exception) throws Exception {

        System.out.println("请求和响应顺利完成");
    }
}

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

package com.study.interceptor;


import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;

/**
 * @author jiyik.com
 */
public class ProductServiceInterceptorAppConfig extends WebMvcConfigurerAdapter {
    @Autowired
    ProductServiceInterceptor productServiceInterceptor;

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

Controller类文件 ProductServiceController.java 的代码如下

package com.study.controller;

import java.util.HashMap;
import java.util.Map;

import com.study.exception.ProductNotFoundException;
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.study.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 类的代码如下所示

package com.study.model;

/**
 * @author jiyik.com
 */
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 的代码如下所示

package com.study;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

/**
 * @author jiyik.com
 */
@SpringBootApplication
public class MyApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyApplication.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.spring</groupId>
    <artifactId>springBootProject</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.6.6</version>
    </parent>

    <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.study'
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')
}

这里我们使用 IDEA 来启动服务（读者也可以使用 mvn clean install 或者 gradle clean build 生成可执行jar包）

接下来在 apifox 应用程序中访问以下 URL，我们可以看到如下所示的输出 -

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

在控制台窗口中，我们可以看到在拦截器中添加的 System.out.println 语句，如下面所示