Feign 是一个声明式的伪RPC的REST客户端，它用了基于接口的注解方式，很方便的客户端配置，刚开始使用时还不习惯，感觉是在客户端写服务端的代码，Spring Cloud 给 Feign 添加了支持Spring MVC注解，并整合Ribbon及Eureka进行支持负载均衡。
Feign的使用很简单，有以下几步：
1、添加依赖
2、启动类添加 @EnableFeignClients 注解支持
3、建立Client接口，并在接口中定义需调用的服务方法
4、使用Client接口。
具体如下首先先添加feign需要的依赖
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1、添加 spring-cloud-starter-openfeign 依赖
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>
完整的 pom.xml
<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.2.0.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.xu</groupId>
<artifactId>service-consumer-feign</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>service-consumer-feign</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>1.8</java.version>
<spring-cloud.version>Hoxton.M3</spring-cloud.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
<exclusions>
<exclusion>
<groupId>org.junit.vintage</groupId>
<artifactId>junit-vintage-engine</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>fastjson</artifactId>
<version>1.2.48</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</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>
<repositories>
<repository>
<id>spring-milestones</id>
<name>Spring Milestones</name>
<url>https://repo.spring.io/milestone</url>
</repository>
</repositories>
</project>
2、启动类添加 @EnableFeignClients 注解支持
package com.xu.serviceconsumer;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.cloud.openfeign.EnableFeignClients;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;
@SpringBootApplication
@EnableDiscoveryClient
@EnableFeignClients
public class ServiceConsumerFeignApplication {
public static void main(String[] args) {
SpringApplication.run(ServiceConsumerFeignApplication.class, args);
}
@Bean
@LoadBalanced
RestTemplate restTemplate() {
return new RestTemplate();
}
}
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3、建立Client接口，并在接口中定义需调用的服务方法
package com.xu.serviceconsumer.service;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
@FeignClient(name = "service-hello")
public interface UserFeignClient {
@RequestMapping(value="/hi",method = RequestMethod.GET)
String getName(@RequestParam String name);
}
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说明：>> name="service-hello"，这里的"service-hello"是注册到Eureka 中的要调用的应用名
>> @GetMapping("/hi") 这里的“/hi”是要调用的应用里的相应的方法（这里需注意，如果service-hello服务下面的 访问路径是 /hi/hello ，则这里也要写"/hi/hello"）。
4、使用Client接口
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package com.xu.serviceconsumer.controller;
import com.alibaba.fastjson.JSONObject;
import com.fasterxml.jackson.databind.util.JSONPObject;
import com.xu.serviceconsumer.service.HelloService;
import com.xu.serviceconsumer.service.UserFeignClient;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.loadbalancer.LoadBalancerClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;
import java.util.HashMap;
import java.util.Map;
@RestController
public class HelloControler {
private static final Logger LOGGER = LoggerFactory.getLogger(HelloControler.class);
@Autowired
private HelloService helloService;
@Autowired
private LoadBalancerClient loadBalancerClient;
@Autowired
private UserFeignClient userFeignClient;
@RequestMapping(value = "/hi")
public String hi(@RequestParam String name) {
return helloService.hiService(name);
}
@RequestMapping(value = "/hello")
public String hello(@RequestParam String name) {
return userFeignClient.getName(name);
}
@RequestMapping(value = "/log-instance")
public Object logInstance() {
ServiceInstance serviceInstance = this.loadBalancerClient.choose("SERVICE-HELLO");
LOGGER.info("{}:{}:{}", serviceInstance.getServiceId(),
serviceInstance.getHost(),serviceInstance.getPort());
JSONObject object1 = new JSONObject();
object1.put("ServiceId",serviceInstance.getServiceId());
object1.put("Host",serviceInstance.getHost());
object1.put("Port",serviceInstance.getPort());
return object1.toJSONString();
}
}
打开浏览器，访问上面Controller中的RestApi请求http://localhost:8767/hello?name=Ronnie结果如下：
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看到这里显然我们的请求响应成功了，成功调用了服务提供者的服务，本节课程到此就结束了，各位如有疑问请再下方留言，我会尽快答复，谢谢观赏！
原文：https://www.cnblogs.com/xulijun137/p/12209731.html