通过在@FeignClient(value = "service-hi",fallback = UserServiceBack.class ) 的fallback属性实现。

1、service-hello项目pom文件增加
···
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
</dependency>
···
完整如下

<?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>com.cloud</groupId>
        <artifactId>cloud-parent</artifactId>
        <version>1.0-SNAPSHOT</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.cloud</groupId>
    <artifactId>service-hello</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>service-hello</name>

    <properties>
        <java.version>1.8</java.version>
    </properties>

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

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-netflix-eureka-client</artifactId>
            <scope>compile</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
        </dependency>

    </dependencies>

</project>

2、启动类增加注解@EnableHystrix

package com.cloud.service.hello;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.netflix.hystrix.EnableHystrix;
import org.springframework.cloud.openfeign.EnableFeignClients;

@EnableFeignClients
@EnableEurekaClient
@EnableDiscoveryClient
@SpringBootApplication
@EnableHystrix
public class ServiceHelloApplication {

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

}

3、配置文件把hystrix开关打开

spring:
  application:
    name: service-hello
server:
  port: 8763

eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka
feign:
  hystrix:
    enabled: true

4、userService接口增加fallback配置

package com.cloud.service.hello;

import com.cloud.service.hello.backup.UserServiceBack;
import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;

/**
 * @author: zhouwei
 * @version: v1.0
 * @description: com.cloud.service.hello
 * @date:2021-01-25
 */
@FeignClient(value = "service-hi",fallback = UserServiceBack.class ) //要调用的服务的名称
public interface UserService {
    @GetMapping("/user/{id}") //mapping地址
     String getUser(@RequestParam long id);


}

5、UserServiceBack实现UserService接口

package com.cloud.service.hello.backup;

import com.cloud.service.hello.UserService;
import org.springframework.stereotype.Component;

/**
 * @author: zhouwei
 * @version: v1.0
 * @description: com.cloud.service.hello.backup
 * @date:2021-01-25
 */
@Component
public class UserServiceBack implements UserService {
    @Override
    public String getUser(long id) {
        return "走到fallback里面来了";
    }
}

停掉service-hi服务，访问

image.png