概述

什么是Feign？与 Ribbon ⼀样，Feign 也是由 Netflflix 提供的，Feign 是⼀个声明式、模版化的 Web Service 客户端，它简化了开发者编写 Web 服务客户端的操作，开发者可以通过简单的接⼝和注解来调⽤ HTTP API， Spring Cloud Feign，它整合了 Ribbon 和 Hystrix，具有可插拔、基于注解、负载均衡、服务熔断等⼀系列便捷功能。

特点

（1）Feign 是⼀个声明式的 Web Service 客户端；

（2）⽀持 Feign 注解、Spring MVC 注解、JAX-RS 注解；

（3）Feign 基于 Ribbon 实现，使⽤起来更加简单；

（4）Feign 集成了 Hystrix，具备服务熔断降级的功能。

示例

1.首先创建服务端项目，提供数据接口。

1.jpg

pom.xml

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.4.3</version>
    <relativePath/> <!-- lookup parent from repository -->
</parent>

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.16.20</version>
        <scope>provided</scope>
    </dependency>
</dependencies>

application.yaml

server:
  port: 8081
  servlet:
    context-path: /api/server
spring:
  application:
    name: userService

User

@Data
public class User {
    private Long id;
    private String name;
    private Integer age;
}

UserController

@RestController
public class UserController {
    @GetMapping("/getUserInfo")
    public User getUserInfo(){
        User user = new User();
        user.setId(1L);
        user.setName("BanQ");
        user.setAge(21);
        return user;
    }
}

启动类

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

浏览器访问：http://localhost:8081/api/server/getUserInfo

2.jpg

2.创建客户端项目，调用服务端接口。

3.jpg

pom.xml

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.1.12.RELEASE</version>
    <relativePath/> <!-- lookup parent from repository -->
</parent>

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.16.20</version>
        <scope>provided</scope>
    </dependency>
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-openfeign</artifactId>
        <version>2.0.2.RELEASE</version>
    </dependency>
</dependencies>

application.yaml

server:
  port: 8082
  servlet:
    context-path: /api/client

UserFeignClient

@FeignClient(
        name = "userService",
        url = "http://localhost:8081/api/server"
)
public interface UserFeignClient {
    @RequestMapping(value = "/getUserInfo",method = RequestMethod.GET)
    @ResponseBody
    String getUserInfo();
}

TestController

@RestController
public class TestController {

    @Autowired
    private UserFeignClient userFeignClient;

    @GetMapping("/get")
    public String get(){
        return userFeignClient.getUserInfo();
    }
}

启动类

@EnableFeignClients
@SpringBootApplication
public class ClientApplication {
    public static void main(String[] args) {
        SpringApplication.run(ClientApplication.class,args);
    }
}

浏览器访问：http://localhost:8082/api/client/get

4.jpg

这样就实现了通过feign client来调用远程（第三方）接口了。