1.Feign介紹

Feign是一個宣告式的web service客戶端，它使得編寫web service客戶端更為容
易。建立介面，為介面添加註解，即可使用Feign。Feign可以使用Feign註解或者
JAX-RS註解，還支援熱插拔的編碼器和解碼器。Spring Cloud為Feign添加了
Spring MVC的註解支援，並整合了Ribbon和Eureka來為使用Feign時提供負載均衡。

譯自：http://projects.spring.io/spring-cloud/docs/1.0.3/springcloud.
html#spring-cloud-feign

2.示例

建立一個Maven專案，並在pom.xml新增如下內容：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="ht
tp://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://m
aven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</
 
modelVersion>
	<artifactId>microservice-consumer-movie-feign</artifactId>
	<packaging>jar</packaging>
<parent>
<groupId>com.itmuch.cloud</groupId>
	<artifactId>spring-cloud-microservice-study</artifactId>
	<version>0.0.1-SNAPSHOT</version>
 

</parent>
<dependencies>
	<dependency>
		<groupId>org.springframework.cloud</groupId>
		<artifactId>spring-cloud-starter-eureka</artifactId>
	</dependency>
	<dependency>
		<groupId>org.springframework.cloud</groupId>
		<artifactId>spring-cloud-starter-feign</artifactId>
	</dependency>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-actuator</artifactId>
	</dependency>
</dependencies>
</project>

• 啟動類：MovieFeignApplication.java

/**
* 使用@EnableFeignClients開啟Feign
* @author eacdy
*/
@SpringBootApplication
@EnableFeignClients
@EnableDiscoveryClient
public class MovieFeignApplication {
	public static void main(String[] args) {
		SpringApplication.run(MovieFeignApplication.class, args);
	}
}

• 實體類：User.java

public class User {
	private Long id;
	private String username;
	private Integer age;
	...
	// getters and setters
}

• Feign測試類：UserFeignClient.java

/**
* 使用@FeignClient("microservice-provider-user")註解繫結microserv
ice-provider-user服務，還可以使用url引數指定一個URL。
* @author eacdy
*/
@FeignClient(name = "microservice-provider-user")
public interface UserFeignClient {
	@RequestMapping("/{id}")
	public User findByIdFeign(@RequestParam("id") Long id);
	}
}

• Feign的測試類：FeignController.java

@RestController
public class FeignController {
	@Autowired
	private UserFeignClient userFeignClient;
	@GetMapping("feign/{id}")
		public User findByIdFeign(@PathVariable Long id) {
		User user = this.userFeignClient.findByIdFeign(id);
		return user;
	}
}

• application.yml

server:
	port: 8020
spring:
	application:
		name: microservice-consumer-movie-feign
eureka:
	client:
		serviceUrl:
			defaultZone: http://discovery:8761/eureka/
instance:
	preferIpAddress: true
ribbon:
	eureka:
		enabled: true 
# 預設為true。如果設定為false，Ribbon將不會從Eureka中獲得服務列表，
#而是使用靜態配置的服務列表。
#靜態服務列表可使用：<client>.ribbon.listOfServers來指定。
#參考：http://projects.spring.io/spring-cloud/docs/1.0.3/spring-cloud.html#spring-cloud-ribbonwithout-eureka
### 參考：https://spring.io/guides/gs/client-side-load-balancing/

Feign程式碼地址：
http://git.oschina.net/itmuch/spring-cloud-study/tree/master/microserviceconsumer-
movie-feign https://github.com/eacdy/spring-cloudstudy/
tree/master/microservice-consumer-movie-feign