SpringCloud---Feign(消费端的调用框架)

介绍

Feign是一个公开的Web服务客户端。它使编写Web服务客户机更容易。用Feign创建接口和注释。它具有可拔插的注释支持，包括Feign的注释和JAX-RS注释。Feign还支持热插拔编码器和解码器。Spring Cloud添加注释的支持和使用Spring MVC的Spring Web默认使用相同的httpmessageconverters。springCloud集成了Ribbon和Eureka提供负载平衡的HTTP客户端使用Feign

简单使用（Spring mvc的注解）

1. 启动类添加@EnableFeignClients注解

@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients
public class MovieFeignApplication {

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

2. 创建Client，是用Spring mvc注解

//user-provider是服务提供者user的applicationName
@FeignClient("user-provider")
public interface UserClient {
    @RequestMapping(value = "/getUser/{id}", method = RequestMethod.GET)
    User getUser(@PathVariable(value = "id") Integer id);

    @RequestMapping(value = "/changeUser", method = RequestMethod.POST)
    User changeUser(@RequestBody User user);

}

这里需要注意一下：

1. RequestMapping不能使用GetMapping代替；
   》2. @PathVariable中必须给出明确的value值；

3. 调用

@RestController
public class MovieController {

    @Autowired
    private UserClient userClient;

    @GetMapping("/movie/{id}")
    public User getUser(@PathVariable Integer id) {
        return userClient.getUser(id);
    }

    @GetMapping(value = "/changeUser")
    public User chanageUser(User user) {
        return userClient.changeUser(user);
    }
}

使用Feign的注解

1. 添加Configration类

@Configuration
public class FooConfigration {

    @Bean
    public Contract feignContract() {
        return new feign.Contract.Default();
    }
}

2. 修改 Client类

@FeignClient(name = "user-provider", configuration = FooConfigration.class)
public interface UserClient {

//    @RequestMapping(value = "/getUser/{id}", method = RequestMethod.GET)
//    User getUser(@PathVariable(value = "id") Integer id);

//    @RequestMapping(value = "/changeUser", method = RequestMethod.POST)
//    User changeUser(@RequestBody User user);


    @RequestLine("GET /getUser/{id}")
    User getUser(@Param("id") Integer id);

}

1. 修改@FeignClient(name = "user-provider", configuration = FooConfigration.class)；
2. 使用Fegin的注解 @RequestLine("GET /getUser/{id}")
3. 使用Fegin 的注解@Param