服务调用之Feign

feign的作用

简化开发，内置robbin实现负载均衡，熔断（需要三步手动配，添加配置文件，在接口上用一个类去写fallback）等机制，使得远程调用其他服务就像调用自己的服务一样便利

第一步：依赖

<?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>2.3.3.RELEASE</version><relativePath/> <!-- lookup parent from repository --></parent><groupId>com.example</groupId><artifactId>consume-service</artifactId><version>0.0.1-SNAPSHOT</version><name>consume-service</name><description>Demo project for Spring Boot</description><properties><java.version>1.8</java.version></properties><dependencies><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-dependencies</artifactId><version>Hoxton.SR8</version><type>pom</type><scope>import</scope></dependency><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-netflix-eureka-client</artifactId><version>2.2.3.RELEASE</version></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId><version>2.3.1.RELEASE</version></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>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-netflix-ribbon</artifactId><version>2.2.5.RELEASE</version></dependency><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-netflix-hystrix</artifactId><version>2.2.5.RELEASE</version></dependency><dependency><groupId>com.netflix.hystrix</groupId><artifactId>hystrix-javanica</artifactId><version>RELEASE</version></dependency><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-openfeign</artifactId><version>2.2.3.RELEASE</version></dependency></dependencies><build><plugins><plugin><groupId>org.springframework.boot</groupId><artifactId>spring-boot-maven-plugin</artifactId></plugin></plugins></build></project>

第二步 加注解

启动类上@EnableFeignClients
创建接口：

package com.example.consumeservice.client;import com.example.consumeservice.pojo.User;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
//底层实现负载均衡
@FeignClient("USER-SERVER")//服务名
public interface Userclient {@RequestMapping("/hello/{id}")//请求User querybyid(@PathVariable("id") int id);//返回值
}

// An highlighted block
var foo = 'bar';

控制器调用接口：

package com.example.consumeservice.Controller;import com.example.consumeservice.client.Userclient;
import com.example.consumeservice.pojo.User;
import com.netflix.hystrix.contrib.javanica.annotation.DefaultProperties;
import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import com.netflix.ribbon.proxy.annotation.Hystrix;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.netflix.ribbon.RibbonLoadBalancerClient;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.client.RestTemplate;@Controller
@DefaultProperties(defaultFallback = "defaultmethod")
public class ConsumerController {
//注入接口@AutowiredUserclient userclient;
//    @Autowired
//    private RestTemplate restTemplate;
//    @Autowired
//    private RibbonLoadBalancerClient client;@RequestMapping("/hello/{id}")@ResponseBodypublic User query(@PathVariable("id") int id){
//        ServiceInstance instanceInfo=client.choose("user-service");
//        List list=discoveryClient.getInstances("USER-SERVER");
//        ServiceInstance instanceInfo=list.get(0)
//        String url="http://"+instanceInfo.getHost()+":"+instanceInfo.getPort()+"/hello";User user=  userclient.querybyid(id);return user;}private String queryfallback(){//方法的参数要和return "不好意思，服务拥挤！";}public String defaultmethod(){return "不好意思，服务拥挤！";}
}

就可以实现调用了

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