在分布式系统当中，服务之间调用关系会随着业务的发展而变的复杂，一个服务可能依赖多个服务，服务之间层层依赖；一个服务的瘫痪可能导致整个系统的崩溃。

与电闸思想类似：每栋房子，每户都安装了电闸，电闸的作用是保证有一家电路出现短路时，电闸进行断电跳闸的操作，这样不至于导致整栋楼用电瘫痪。

<?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">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.cntaiping.tpa</groupId>
    <artifactId>hystrix</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>
    <name>hystrix</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>com.cntaiping.tpa</groupId>
        <artifactId>cloud</artifactId>
        <version>1.0-SNAPSHOT</version>
    </parent>

    <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.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-ribbon</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
        </dependency>
    </dependencies>

</project>

#服务名称
spring.application.name=consumer-hystrix
#端口号
server.port=8505
#在注册中心中进行注册
eureka.client.serviceUrl.defaultZone=http://localhost:8800/eureka/

package com.cntaiping.tpa.hystrix;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.cloud.netflix.hystrix.EnableHystrix;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

@SpringBootApplication
@EnableHystrix
public class HystrixApplication {

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

    @Bean
    @LoadBalanced
    RestTemplate restTemplate() {
        return new RestTemplate();
    }
}

在hello方法上加上@HystrixCommand注解。该注解对该方法创建了熔断器的功能，并指定了fallbackMethod熔断方法，熔断方法直接返回了一个字符串

package com.cntaiping.tpa.hystrix.service;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;

@Service
public class HelloService {
    @Autowired
    RestTemplate restTemplate;

    @HystrixCommand(fallbackMethod = "error")
    public String hello(String name) {
        return restTemplate.getForObject("http://producer/get?name="+name, String.class);
    }

    public String error(String name) {
        return "hi,"+name+",sorry,error!";
    }
}

package com.cntaiping.tpa.hystrix.controller;

import com.cntaiping.tpa.hystrix.service.HelloService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {
    @Autowired
    HelloService helloService;

    @GetMapping(value = "/hello")
    public String hello(@RequestParam String name) {
        return helloService.hello( name );
    }
}