Feign是一個宣告式的Web服務客戶端。能很簡單的呼叫其他服務的API。並且實現負載均衡。

1、建立Feign模組

<?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">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.server</groupId>
    <artifactId>feign</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>feign</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>com.cloud</groupId>
        <artifactId>test</artifactId>
        <version>1.0-SNAPSHOT</version>
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
        <spring-cloud.version>Finchley.RELEASE</spring-cloud.version>
    </properties>

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

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>
 

配置檔案application.yml

eureka:
  client:
    serviceUrl:
      # 註明自己的服務註冊中心的地址
      defaultZone: http://localhost:7777/eureka/
server:
  port: 8005
spring:
  application:
    name: service-feign

在應用主類上表明為eureka-client，向服務註冊中心註冊

@SpringBootApplication
@EnableEurekaClient
//註解開啟Feign
@EnableFeignClients
public class FeignApplication {

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

}
 

建立呼叫介面FeignService

@Service
@FeignClient(value = "service-hello")
public interface FeignService {

    @RequestMapping(value = "/hi",method = RequestMethod.GET)
    String sayHiFromClientOne(@RequestParam(value = "name") String name);
}

@FeignClient(value = “service-hello”)，value 指明要呼叫的服務名
Controller

@RestController
public class HiController {

    @Autowired
    FeignService feignService;

    @RequestMapping(value = "/hi", method = RequestMethod.GET)
    public String sayHi(@RequestParam String name) {
        return feignService.sayHiFromClientOne(name);
    }

}

2、測試

• hi mistra,i am from port:8002
• hi mistra,i am from port:8003

service-feign遠端呼叫了eureka-client的服務，並且實現了負載均衡。

###原始碼

3、FeignClient工作原理

程式啟動時會檢查SpringBoot啟動類是否有@EnableFeignClient註解，如果有，則開啟包掃描，掃描被@FeignClient註解的介面，把介面名和註解資訊賦給BeanDefinitionBuilder，然後根據BeanDefinitionBuilder得到BeanDefinition，最後將BeanDefinition注入到Ioc容器中。通過JDK代理，當呼叫@FeignClient註解接口裡的方法時，該方法會被攔截。在SynchronousMethodHandler類進行攔截處理，會根據引數生成RequestTenplate物件，該物件是Http請求模板。Request物件交給Client處理，網路請求框架可以使HttpURLConnection、HttpClient和OkHttp，最後執行Http請求來獲取響應。最後的Client被封裝到了LoadBalancerClient類，這個類結核Ribbon做到了負載均衡。
Ribbon負載均衡上一篇又說道：Spring Cloud 之 負載均衡 Ribbon元件