Feign是Netflix开发的声明式、模块化的HTTP客户端。Feign可以帮我们更加便捷、优雅的调用HTTP API。
在Spring Cloud中，使用Feign非常简单，创建一个接口，并在接口上添加一些注解，代码就完成了。

基本使用

添加依赖

<dependency>
     <groupId>org.springframework.cloud</groupId>
     <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
</dependency>

<dependency>
     <groupId>org.springframework.cloud</groupId>
     <artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>  

增加配置文件

配置文件与之前类似，不再赘诉。

server:
  port: 8081
eureka:
  instance:
    prefer-ip-address: false
  client:
    service-url:
      defaultZone: http://peer1:8761/eureka,http://peer2:8762/eureka
spring:
  application:
    name: microservice-consumer-movie

修改启动类，增加@EnableFeignClients

@SpringBootApplication
@EnableFeignClients
public class MicroserviceConsumerMovieApplication {

    public static void main(String[] args) {
        SpringApplication.run(MicroserviceConsumerMovieApplication.class, args);
    }
    
}

增加Feign接口

/**
 * 博客：https://lisen.cc
 * Description:
 *
 * @Author: 香草物语
 * DateTime: 2021-07-18 12:52
 */
@FeignClient(name = "microservice-provider-user")
public interface UserFeignClient {

    @RequestMapping(value = "{id}",method = RequestMethod.GET)
    User findById(@PathVariable Long id);

}

调用

@RestController
public class MovieController {

    @Resource
    private DiscoveryClient discoveryClient;

//    @Resource
//    private RestTemplate restTemplate;

    @Resource
    private UserFeignClient userFeignClient;

//    @Resource
//    private LoadBalancerClient loadBalancerClient;

    @GetMapping("/user-instance")
    public List<ServiceInstance> showInfo() {
        return discoveryClient.getInstances("microservice-provider-user");
    }

    @GetMapping("/user/{id}")
    public User findById(@PathVariable Long id) {
//        return restTemplate.getForObject("http://microservice-provider-user/"+id, User.class);
        return userFeignClient.findById(id);
    }

//    @GetMapping("log/microservice-provider-user")
//    public ServiceInstance userLog() {
//        return loadBalancerClient.choose("microservice-provider-user");
//    }

}

基于代码Feign自定义配置

创建配置类

创建Feign的配置类UserFeignConfig，需要注意的是，该类不能添加@Configuration注解，如果添加了@Configuration注解，那么该类不能在主应用程序的@ComponentScan注解扫描包内。

/**
 * 博客：https://lisen.cc
 * Description:feign配置文件
 *
 * @Author: 香草物语
 * DateTime: 2021-07-18 15:39
 */
public class UserFeignConfig {

    /**
     * 将契约改成Feign原生的契约，这样就可以使用Feign自带的注解了
     * @return
     */
    @Bean
    public Contract feignContract(){
        return new Contract.Default();
    }

}

修改Feign接口

/**
 * 博客：https://lisen.cc
 * Description:
 *
 * @Author: 香草物语
 * DateTime: 2021-07-18 12:52
 */
@FeignClient(name = "microservice-provider-user",configuration = UserFeignConfig.class)
public interface UserFeignClient {

    /**
     * 使用Feign自带的注解 @RequestLine
     * @param id
     * @return
     */
    @RequestLine("GET /{id}")
    User findById(@Param("id") Long id);

}

测试

@RestController
public class MovieController {

    @Resource
    private DiscoveryClient discoveryClient;

//    @Resource
//    private RestTemplate restTemplate;

    @Resource
    private UserFeignClient userFeignClient;

//    @Resource
//    private LoadBalancerClient loadBalancerClient;

    @GetMapping("/user-instance")
    public List<ServiceInstance> showInfo() {
        return discoveryClient.getInstances("microservice-provider-user");
    }

    @GetMapping("/user/{id}")
    public User findById(@PathVariable Long id) {
//        return restTemplate.getForObject("http://microservice-provider-user/"+id, User.class);
        return userFeignClient.findById(id);
    }

//    @GetMapping("log/microservice-provider-user")
//    public ServiceInstance userLog() {
//        return loadBalancerClient.choose("microservice-provider-user");
//    }

}

再次访问http://localhost:8081/user/1，查看输出

全局配置

以上我们是根据服务进行配置的，我们也可以进行全局配置。在启动类中添加@EnableFeignClients注解

@SpringBootApplication
@EnableFeignClients(defaultConfiguration = UserFeignConfig.class)
public class MicroserviceConsumerMovieApplication {

    public static void main(String[] args) {
        SpringApplication.run(MicroserviceConsumerMovieApplication.class, args);
    }

}

使用属性自定义Feign配置

配置指定名称的Feign Client

修改配置文件

server:
  port: 8081
eureka:
  instance:
    prefer-ip-address: false
  client:
    service-url:
      defaultZone: http://peer1:8761/eureka,http://peer2:8762/eureka
spring:
  application:
    name: microservice-consumer-movie
feign:
  client:
    config:
      microservice-provider-user:
        contract: feign.Contract.Default

修改Feign接口

@FeignClient(name = "microservice-provider-user")
public interface UserFeignClient {

    /**
     * 使用Feign自带的注解 @RequestLine
     * @param id
     * @return
     */
    @RequestLine("GET /{id}")
    User findById(@Param("id") Long id);

}

配置全局Feign Client

修改配置文件，将指定名称的Feign Client改成default即可。

server:
  port: 8081
eureka:
  instance:
    prefer-ip-address: false
  client:
    service-url:
      defaultZone: http://peer1:8761/eureka,http://peer2:8762/eureka
spring:
  application:
    name: microservice-consumer-movie
feign:
  client:
    config:
      default:
        contract: feign.Contract.Default

Feign对压缩的支持

可以通过以下配置对请求或相应进行压缩。

feign:
  compression:
    request:
      enabled: true
      mime-types: text/xml,application/xml,application/json
      min-request-size: 2048
    response:
      enabled: true

配置Feign日志

feign:
  client:
    config:
      default:
        contract: feign.Contract.Default
        logging-level: full
  compression:
    request:
      enabled: true
      mime-types: text/xml,application/xml,application/json
      min-request-size: 2048
    response:
      enabled: true
logging:
  level:
    cc.lisen.microserviceconsumermovie.service.UserFeignClient: debug