原文連結

Feign簡介

Feign 是一個宣告web服務客戶端，這便得編寫web服務客戶端更容易，使用Feign 建立一個介面並對它進行註解，它具有可插拔的註解支援包括Feign註解與JAX-RS註解，Feign還支援可插拔的編碼器與解碼器，Spring Cloud 增加了對 Spring MVC的註解，Spring Web 預設使用了HttpMessageConverters, Spring Cloud 整合 Ribbon 和 Eureka 提供的負載均衡的HTTP客戶端 Feign.

宣告式REST客戶端：Feign

先要啟動eureka_register_service工程（註冊中心）和biz-service-0工程（服務生產者）

建立一個maven工程eureka_feign_client
pom.xml

<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.4.3.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<
 
properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<java.version>1.8</java.version>
</properties>
<dependencies>
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-
 
starter-feign</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-eureka</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-test</artifactId>
        <scope>test</scope>
    </dependency>
</dependencies>
<dependencyManagement>
    <dependencies>
        <dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-dependencies</artifactId>
    <version>Brixton.SR5</version>
    <type>pom</type>
    <scope>import</scope>
</dependency>
    </dependencies>
</dependencyManagement>

在應用主類中通過@EnableFeignClients註解開啟Feign功能

啟動檔案FeignApplication.java

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

定義服務介面類UserClient.java

使用@FeignClient(“biz-service-0”)註解來繫結該介面對應biz-service-0服務

@FeignClient("biz-service-0")
public interface UserClient {
 
    @RequestMapping(method = RequestMethod.GET, value = "/getuser")
    public User getuserinfo();
     
    @RequestMapping(method = RequestMethod.GET, value = "/getuser")
    public String getuserinfostr();
     
    @RequestMapping(method = RequestMethod.GET, value = "/info")
    public  String  info();
 
}

在web層中呼叫上面定義的UserController，具體如下

@RestController
public class UserController {
 
    @Autowired
    UserClient userClient;
 
    @RequestMapping(value = "/getuserinfo", method = RequestMethod.GET)
    public User getuserinfo() {
        return userClient.getuserinfo();
    }
     
    @RequestMapping(value = "/getuserinfostr", method = RequestMethod.GET)
    public String getuserinfostr() {
        return userClient.getuserinfostr();
    }
     
    @RequestMapping(value = "/info", method = RequestMethod.GET)
    public String info() {
        return userClient.info();
    }
 
 
}

application.properties配置變數

spring.application.name=feign-consumer
server.port=8004
eureka.client.serviceUrl.defaultZone=http://localhost:8000/eureka/

總結

其實通過Feign封裝了HTTP呼叫服務方法，使得客戶端像呼叫本地方法那樣直接呼叫方法，類似Dubbo中暴露遠端服務的方式，區別在於Dubbo是基於私有二進位制協議，而Feign本質上還是個HTTP客戶端