使用OpenFeign+Eureka实现HTTP调用的简单示例

1. 由于RPC调用需要使用注册中心，所以首先需要创建eureka服务，创建SpringBoot项目后导入spring-cloud-starter-netflix-eureka-server，注意SpringBoot和SpringCloud版本一致性，然后进行配置，启动类添加注解@EnableEurekaServer

<dependency>
	<groupId>org.springframework.cloud</groupId>
	<artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
</dependency>

server:
  port: 8761

spring:
  application:
    name: eureka

eureka:
  client:
    register-with-eureka: false # 不向Eureka注册自己
    fetch-registry: false       # 不从Eureka获取注册信息
  service-url:
    defaultZone: http://localhost:8761/eureka/

@SpringBootApplication
@EnableEurekaServer
public class EurekaApplication {

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

}

2. 创建服务提供者SpringBoot应用，关键是导入spring-cloud-starter-netflix-eureka-client依赖，进行eureka的配置，编写controller接入层代码，启动类不需要加@EnableEurekaClient注解，因为在新版本中已经被移除

<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-web</artifactId>
</dependency>

<dependency>
	<groupId>org.springframework.cloud</groupId>
	<artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
</dependency>

server:
  port: 8082

spring:
  application:
    name: producer

eureka:
  client:
    register-with-eureka: true
    fetch-registry: true
  service-url:
    defaultZone: http://localhost:8761/eureka/

@RestController
@RequestMapping("/api")
public class DataController {

    @GetMapping("/data")
    public String getData() {

        System.out.println("服务提供者被调用");
        return "Hello from Producer!";
    }
}

3. 创建服务消费者SpringBoot应用，引入如下三个关键依赖，进行eureka配置，编写接口，编写接入层代码调用该接口，启动类需要加上@EnableFeignClients

<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
	<groupId>org.springframework.cloud</groupId>
	<artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>

<dependency>
	<groupId>org.springframework.cloud</groupId>
	<artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
</dependency>

server:
  port: 8083

spring:
  application:
    name: consumer

eureka:
  client:
    register-with-eureka: true
    fetch-registry: true
  service-url:
    defaultZone: http://localhost:8761/eureka/

@FeignClient(name = "producer") // 此处不需要写url = "http://localhost:8082"，因为通过注册中心调用
public interface ProducerClient {

    @GetMapping("/api/data")
    String getData();
}

@RestController
@RequestMapping("/consumer")
public class ConsumerController {

    @Autowired
    private ProducerClient producerClient;

    @GetMapping("/data")
    public String getDataFromProducer() {
        return producerClient.getData();
    }
}

@SpringBootApplication
@EnableFeignClients
public class ConsumerApplication {

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

}

4. 总结

• 通过引入eureka注册中心后，如果服务提供者有多个节点，那么请求就会被发送到存活的节点上，实现了动态路由，避免因为固定写url但是该节点宕机导致调用失败的问题
• Feign并不是RPC(远程过程调用)，本质上还是基于HTTP，就算是因为服务提供者的api.jar，调用期中的接口，也只是基于HTTP协议的调用，只是不用写HTTP客户端，一切都是组件通过动态代理生成的