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SpringCloud组件之Feign

Feign是一个声明式的伪Http客户端，它使得写Http客户端变得更简单。使用Feign，只需要创建一个接口并注解。它具有可插拔的注解特性，可使用Feign 注解和JAX-RS注解。Feign支持可插拔的编码器和解码器。Feign默认集成了Ribbon，并和Eureka结合，默认实现了负载均衡的效果。简而言之：

Feign 采用的是基于接口的注解;
Feign 整合了ribbon，具有负载均衡的能力;
整合了Hystrix，具有熔断的能力.

2.创建Feign调用演示工程

2.1 准备工作

启动上篇中Eureka演示工程中Eureka Server与Eureka Client Provider服务并在Eureka Client Provider中Controller增加一个接口用于Feign调用测试

@RestController
@RequestMapping("/demo")
public class DemoController {

    @Value("${server.port:#{null}}")
    private String serverPort;

    @GetMapping("/hello")
    public String hello() {
        return "Hello " + serverPort;
    }

    @GetMapping("/feign")
    public String feignTest(@RequestParam(value = "name") String name){
        return "Hello Feign "+ name;
    }

}
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2.2 创建一个服务消费者

新建一个maven工程，取名为：spring-cloud-feign-demo,添加如下依赖pom.xml中

<?xml version="1.0" encoding="UTF-8"?>
<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">
    <parent>
        <artifactId>spring-cloud-demo</artifactId>
        <groupId>com.hxmec</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>spring-cloud-feign-demo</artifactId>

    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>
        <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>
    </dependencies>
</project>
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新建application.yml，增加下面的配置

server:
  port: 9003
spring:
  application:
    name: feign-demo
logging:
  pattern:
    console: '%d{yyyy-MM-dd HH:mm:ss.SSS} %-5level [%thread] %logger{15} - %msg%n'
eureka:
  client:
    service-url:
      defaultZone: http://localhost:8888/eureka/
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创建一个启动类 FeignDemoApplication，添加Feign相关注解

@SpringBootApplication
@EnableEurekaClient
@EnableDiscoveryClient
@EnableFeignClients
public class FeignDemoApplication {

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

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编写Feign接口服务

@FeignClient(value = "eureka-client-provider")//此名称为消费提供者注册的服务名称
public interface FeignService {

    @RequestMapping(value = "/demo/feign",method = RequestMethod.GET)
    String feignTest(@RequestParam(value = "name") String name);
}

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编写Controller层调用Feign接口实例

@RestController
@RequestMapping("/feign")
@AllArgsConstructor
public class FeignClientController {

    private final FeignService feignService;

    @GetMapping(value = "/test1")
    public String feign(@RequestParam String name) {
        return feignService.feignTest(name);
    }

}
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启动项目，打开http://localhost:8888可以看到应用已经注册到Eureka注册中心