一、代码示例

说明：此处使用的SpringBoot版本为2.1.13.RELEASE，SpringCloud版本为Greenwich.SR5
此处不再贴server与client代码。
1、maven依赖

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

2、application.yml
增加配置
feign:
hystrix:
enabled: true

server:
  port: 9005
spring:
  application:
    name: feign-hystrix
eureka:
  instance:
    hostname: localhost
    prefer-ip-address: true
    instance-id: feign-hystrix-9005
  client:
    service-url:
      defaultZone: http://eureka7001:7001/eureka/,http://eureka7002:7002/eureka/,http://eureka7003:7003/eureka/
feign:
  hystrix:
    enabled: true
#info信息
info:
  app:
    name: feign-hystrix-9005
  company:
    name: www.xxx.com
  build:
    artifactId: ${project.artifactId}
    version: ${project.version}

3、启动类

package org.example;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.hystrix.EnableHystrix;
import org.springframework.cloud.openfeign.EnableFeignClients;

@SpringBootApplication
@EnableFeignClients
public class FeignHystrix9005Application {
    public static void main(String[] args) {
        SpringApplication.run(FeignHystrix9005Application.class,args);
    }
}

4、其他java类
定义接口FeignService ，增加@FeignClient，指明调用的服务，以及fallback

@FeignClient(value = "CLIENT",fallback = FeignServiceFallback.class)
public interface FeignService {
    @GetMapping("/hello/{name}")
    public String hello(@PathVariable("name") String name);
}

增加FeignService 接口的FeignServiceFallback,该类需注入到容器

package org.example.service;

import org.springframework.stereotype.Component;

@Component
public class FeignServiceFallback implements FeignService{

    @Override
    public String hello(String name) {
        return "helloError,"+name;
    }
}

Controller类

package org.example.controller;

import org.example.service.FeignService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class FeignHystrixController {

    @Autowired
    private FeignService feignService;

    @GetMapping("/hello/{name}")
    public String hello(@PathVariable String name){
        return feignService.hello(name);
    }
}

2、测试验证

先后启动server、client和本服务，访问http://localhost:7001/

image.png
再访问http://localhost:9005/hello/zs
image.png
然后，停止client,再次访问
image.png
表明代码生效。
github:
https://github.com/panli1988/cloud01
https://github.com/panli1988/cloud02
参考：
https://blog.csdn.net/forezp/article/details/70148833
http://www.itmuch.com/spring-cloud/spring-cloud-index/
还有尚硅谷周阳老师的视频