实现demo步骤如下

1.创建在spring-cloud-demo下创建hystrix-fallback模块

pom，从feigin中copy过来（hystrix是一个服务调用者，所以要调用feigin-client）

<?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">
    <parent>
        <artifactId>spring-cloud-demo</artifactId>
        <groupId>org.example</groupId>
        <version>1.0.0-SNAPSHOT</version>
        <relativePath>../../pom.xml</relativePath>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.imooc</groupId>
    <artifactId>hystrix-fallback</artifactId>
    <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-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>

        <dependency>
            <groupId>com.imooc</groupId>
            <artifactId>feign-client-intf</artifactId>
            <version>1.0.0-SNAPSHOT</version>
        </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.cloud</groupId>
            <artifactId>spring-cloud-openfeign-core</artifactId>
        </dependency>
    </dependencies>

</project>

2.创建hystrix启动类(4个注解？)

HystrixFallbackApplication：

package com.imooc.springcloud;

import org.springframework.boot.WebApplicationType;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.openfeign.EnableFeignClients;

/**
 * Created by 半仙.
 */
@EnableDiscoveryClient
@SpringBootApplication
@EnableFeignClients
@EnableCircuitBreaker
public class HystrixFallbackApplication {

    public static void main(String[] args) throws NoSuchMethodException {
        new SpringApplicationBuilder(HystrixFallbackApplication.class)
                .web(WebApplicationType.SERVLET)
                .run(args);

//        System.out.println(Feign.configKey(MyService.class,
//                MyService.class.getMethod("retry", int.class)));
    }

}

3.定义一个接口MyService，与“害群之马”联系上，并且加上fallback

MyService：

package com.imooc.springcloud;

import org.springframework.cloud.openfeign.FeignClient;

@FeignClient(name = "feign-client",fallback = "Fallback.class")
public interface MyService extends IService {
}

4.定义一个Hystrix的fallback类

//超时也算是一种错误
1.创建包com/imooc/springcloud/hystrix
2.创建Fallback类

Fallback类实现上面创建的MyService的接口，实现error接口的静默

package com.imooc.springcloud.hystrix;

import com.imooc.springcloud.Friend;
import com.imooc.springcloud.MyService;
import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;

@Slf4j
@Component
public class Fallback implements MyService {

    @Override
    public String error() {
        log.info("Fallback:I am not a back sheep any more")
        return "Fallback:I am not a back sheep any more";
    }

    @Override
    public String sayHi() {
        return null;
    }

    @Override
    public Friend sayHiPost(Friend friend) {
        return null;
    }

    @Override
    public String retry(int timeout) {
        return null;
    }
}

5.创建Controller

package com.imooc.springcloud;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class Controller {

    @Autowired
    private MyService myService;

    @GetMapping("/fallback")
    public String fallback(){
        return myService.error();
    }


}

6.在feign-client-intf模块创建error方法(创建服务提供者)

IService：

package com.imooc.springcloud;

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestParam;

/**
 * Created by 半仙.
 */
@FeignClient("feign-client")
public interface IService {

    @GetMapping("/sayHi")
    public String sayHi();

    @PostMapping("/sayHi")
    public Friend sayHiPost(@RequestBody Friend friend);

    @GetMapping("/retry")
    public String retry(@RequestParam(name = "timeout") int timeout);

    @GetMapping("/error")
    public String error();

}

IService的实现方法Controller（定义一个害群之马）：

package com.imooc.springcloud;

import lombok.extern.slf4j.Slf4j;
import org.apache.commons.logging.Log;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

/**
 * Created by 半仙.
 */
@RestController
@Slf4j
public class Controller implements IService {

    @Value("${server.port}")
    private String port;


    @GetMapping("/sayHi2")
    public String sayHi2() {
        return "This is " + port;
    }

    @Override
    public String sayHi() {
        return "This is " + port;
    }

    @Override
    public Friend sayHiPost(@RequestBody Friend friend) {
        log.info("You are " + friend.getName());
        friend.setPort(port);
        return friend;
    }

    @Override
    public String retry(@RequestParam(name = "timeout") int timeout) {
        while (--timeout >= 0) {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
            }
        }
        log.info("retry " + port);
        return port;
    }

    @Override
    public String error() {
        throw new RuntimeException("black sheep");
    }
}

7.配置文件

application.properties ：

spring.application.name=hystrix-consumer
server.port=50000
spring.main.allow-bean-definition-overriding=true
eureka.client.serviceUrl.defaultZone=http://localhost:20000/eureka/

# 开启Feign下面的Hystrix功能
feign.hystrix.enabled=true
# 是否开启服务降级
hystrix.command.default.fallback.enabled=true