版权声明：lpf https://blog.csdn.net/justlpf/article/details/84338799
什么是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。注意：负载均衡是加在客户端中，而不是服务端中。
简而言之：
Feign 采用的是基于接口的注解
Feign 整合了ribbon
代码实现及演示效果
注册中心（略）
1、在客户端添加依赖包
<?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.cloud</groupId>-->
<artifactId>consumer-srv</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<name>consumer-srv</name>
<description>consumer-srv</description>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.0.2.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</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.SR2</spring-cloud.version>
</properties>
<dependencies>
<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>
<!--增加feign的依赖, feign依赖ribbon-->
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-feign</artifactId>
<version>1.4.6.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
<!-- 修改后立即生效, 热部署 -->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>springloaded</artifactId>
<version>1.2.8.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</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>
<configuration>
<!-- 没有该配置，devtools 不生效 -->
<fork>true</fork>
<addResources>true</addResources>
</configuration>
</plugin>
<!-- spring Boot在编译的时候，是有默认JDK版本的，这里自定义指定JDK版本 -->
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<configuration>
<archive>
<manifest>
<addClasspath>true</addClasspath>
<classpathPrefix>lib/</classpathPrefix>
<mainClass>com.yame.Application</mainClass>
<useUniqueVersions>false</useUniqueVersions>
</manifest>
<manifestEntries>
<Class-Path>./</Class-Path>
</manifestEntries>
</archive>
</configuration>
</plugin>
</plugins>
</build>
<!--远程仓库-->
<repositories>
<repository>
<id>spring-snapshots</id>
<name>Spring Snapshots</name>
<url>https://repo.spring.io/snapshot</url>
<snapshots>
<enabled>true</enabled>
</snapshots>
</repository>
<repository>
<id>spring-milestones</id>
<name>Spring Milestones</name>
<url>https://repo.spring.io/milestone</url>
<snapshots>
<enabled>false</enabled>
</snapshots>
</repository>
</repositories>
</project>
2、在客户端启动类中使用@EnableFeignClients开启feignClient功能
@EnableEurekaClient
@EnableFeignClients
@SpringBootApplication
public class ServiceAApplication {
public static void main(String[] args) {
SpringApplication.run(ServiceAApplication.class, args);
}
}3、在客户端中新建一个ServiceAFeignClient接口调用service-b的服务
package com.example.servicea;
import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
/**
* feign默认集成了ribbon, 所以这里如果存在两个service-b微服务时, 会自动启用负载均衡策略
* Ribbon负债均衡默认使用的是轮询机制
*/
@Component
@FeignClient(value = "service-b") //这里的name对应调用服务的spring.applicatoin.name
public interface ServiceAFeignClient {
@RequestMapping(value = "/hi")
String hi(@RequestParam("id") String id);
}4、在客户端系统中写一个测试controller
@RestController
public class TestController {
@Autowired
ServiceAFeignClient serviceAFeignClient;
@RequestMapping("/hi")
public String hi(@RequestParam String id){
return serviceAFeignClient.hi(id);
}
}5、在服务端系统中提供一个hi()方法，供客户端调用
@EnableEurekaClient
@RestController
@SpringBootApplication
public class ServiceBApplication {
public static void main(String[] args) {
SpringApplication.run(ServiceBApplication.class, args);
}
@Value("${spring.application.name}")
private String name;
@Value("${server.port}")
private String port;
@RequestMapping("/hi")
public String hi(@RequestParam String id){
return "hi, " + id + ", " + name + ":" + port;
}
}6、新建一个服务service-b-2，代码和service-b完全一致，只需改端口号（服务名也叫service-b，spring.application.name=service-b）
在idea中可以不新建工程，新建两个springboot运行实例, 分别使用两个端口号(8081, 8082)启动。
启动后会在Eureka注册中心中看到service-b有两个，一个端口号为8081，一个为8082：
DS Replicas
Instances currently registered with Eureka
7、查看效果
访问：http://localhost:8083/hi?id=123
返回：hi, 123, service-b:8082
刷新：hi, 123, service-b:8081
刷新：hi, 123, service-b:8082
刷新：hi, 123, service-b:8081
因为Ribbon负债均衡默认使用的是轮询机制。