spring Cloud-Feign调用远端HTTP服务

采用Feign的方式来调用Hello World服务集群。

1. 创建Maven工程，加入spring-cloud-starter-feign依赖

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

2. 创建启动类，需呀加上@EnableFeignClients注解以使用Feign， 使用@EnableDiscoveryClient开启服务自动发现

package springcloud.helloworld.feign.service;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.netflix.feign.EnableFeignClients;

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

3. 添加配置文件application.yml, 使用端口8902, 名字定义为service-feign, 并注册到eureka服务中心

eureka:
   client:
      serviceUrl:
        defaultZone: http://localhost:8761/eureka/
server:
   port: 8902
spring:
   application:
      name: service-feign

4. 定义Feign：一个用@FeignClient注解的接口类,

package springcloud.helloworld.feign.service;

import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

@FeignClient(value = "SERVICE-HELLOWORLD")
public interface HelloWorldService {
    @RequestMapping(value = "/",method = RequestMethod.GET)
    String sayHello();
}

5. 定义一个WebController。

sayHello()映射到http://localhost:8902/hello, 在这里，我修改了Hello World服务的映射，将根“/”， 修改成了“/hello”。

package springcloud.helloworld.feign.service;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class WebController {
    @Autowired 
　　 HelloWorldService helloWorldFeignService;
    @RequestMapping(value = "/hello",method = RequestMethod.GET)
    public String sayHello(){
        return helloWorldFeignService.sayHello();
    }
}

6. 启动Feign应用， 访问http://localhost:8902/hello， 多次刷新，可以看到和前一章Ribbon里面的应用一样， 两个Hello World服务的输出交替出现。说明通过Feign访问服务， Spring Cloud已经缺省使用了Ribbon负载均衡。