JavaEE進階知識學習-----SpringCloud（七）Feign負載均衡

Feign負載均衡

Feign是一個聲明式WebService客戶端，使用Feign可以讓編寫Web Service客戶端變得更簡單，它的使用方法就是定義一個接口，而後在上面添加註解。SpringCloud對Feign進行了封裝，支持SpringMVC註解和HTTPMessageConverters，Feign能夠與Eureka和Ribbon組合使用以支持負載均衡。簡單講，只須要建立一個接口，而後在上面使用註解便可。

Feign使用步驟

參考項目microservicecloud-consumer-dept-80新建microservicecloud-consumer-dept-feign,拷貝相應的包和配置文件，去掉IRule等信息，修改pom.xml文件，添加對Feign的支持

pom.xml文件

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <parent>
    <groupId>com.luo.springcloud</groupId>
    <artifactId>microservicecloud</artifactId>
    <version>0.0.1-SNAPSHOT</version>
  </parent>
  <artifactId>microservicecloud-consumer-dept-feign</artifactId>
<dependencies>
		<dependency><!-- 本身定義的api -->
			<groupId>com.luo.springcloud</groupId>
			<artifactId>microservicecloud-api</artifactId>
			<version>${project.version}</version>
		</dependency>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-feign</artifactId>
		</dependency>
		<!-- Ribbon相關 -->
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-eureka</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-ribbon</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-config</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
		<!-- 修改後當即生效，熱部署 -->
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>springloaded</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-devtools</artifactId>
		</dependency>
	</dependencies>
</project>
複製代碼

因爲Feign是面向接口編程，爲方便接口的互相調用，將接口和公共的方向在項目microservicecloud-api中，所以修改成：

修改microservicecloud-api工程的pom.xml文件

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

新建DeptClientService接口

@FeignClient(value = "MICROSERVICECLOUD-DEPT")
public interface DeptClientService {
	@RequestMapping(value = "/dept/get/{id}",method = RequestMethod.GET)
	public Dept get(@PathVariable("id") long id);
	
	@RequestMapping(value = "/dept/list",method = RequestMethod.GET)
	public List<Dept> list();
	
	@RequestMapping(value = "/dept/add", method = RequestMethod.POST)
	public boolean add(Dept dept);
}
複製代碼

修改microservicecloud-consumer-dept-feign中Controller添加新建的DeptClientService

@RestController
public class DeptController_Consumer {
	@Autowired
	private DeptClientService service;
	
	@RequestMapping(value = "/consumer/dept/get/{id}")
	public Dept get(@PathVariable("id") Long id){
		return this.service.get(id);
	}
	
	@RequestMapping(value = "/consumer/dept/list")
	public List<Dept> list(){
		return this.service.list();
	}
	
	@RequestMapping(value = "/consumer/dept/add")
	public Object add(Dept dept){
		return this.add(dept);
	}
}
複製代碼

修改microservicecloud-consumer-dept-feign主啓動類,添加註解

@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients(basePackages = {"com.luo.springcloud"})
@ComponentScan("com.luo.springcloud")
public class DeptConsumer80_Feign_App {
	public static void main(String[] args) {
		SpringApplication.run(DeptConsumer80_Feign_App.class, args);
	}
}
複製代碼

測試

啓動3個Eureka集羣，啓動三個部門微服務提供者，啓動Feign，訪問http://localhost/consumer/dept/list便可

總結說明

Feign集成了Ribbon，利用Ribbon維護了MicroServiceCloud-Dept的服務列表信息，並經過輪詢的方式實現了客戶端的複雜均衡，與Ribbon不一樣的是，經過Feign只須要定義服務綁定接口且以聲明式法人方法，優雅而簡單的實現服務調用。