Hystrix会监控微服务的调用状况，失败调用达到一定阀值时，会启用熔断机制

开发环境

• JDK8+
• Gradle4+
• Spring Boot 2.0.0.M3
• Spring Cloud Starter Netflix Eureka Client Finchley.M2
• Spring Cloud Starter OpenFeign Finchley.M2
• Spring Cloud Starter Netflix Hystrix Finchley.M2

创建项目

以之前的micro-weather-eureka-client-feign为蓝本，创建micro-weather-eureka-client-feign-hystrix项目

修改源码

修改build.gradle配置，添加Hystrix依赖：

//依赖关系
dependencies {

    //Eureka Client
    compile('org.springframework.cloud:spring-cloud-starter-netflix-eureka-client')

    //Feign
    compile('org.springframework.cloud:spring-cloud-starter-openfeign:2.0.0.M3')

    //Hystrix
    compile('org.springframework.cloud:spring-cloud-starter-netflix-hystrix')

    //该依赖用于测试阶段
    testCompile('org.springframework.boot:spring-boot-starter-test')
}

修改com.study.spring.cloud.weather包下的Application类，加入@EnableCircuitBreaker注解：

package com.study.spring.cloud.weather;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.netflix.feign.EnableFeignClients;

/*
 * @SpringBootApplication注解声明Spring Boot应用
 * 作用等同于@Configuration, @EnableAutoConfiguration, @ComponentScan，
 * 简化Spring配置
*/
@SpringBootApplication
//启用可发现的客户端
@EnableDiscoveryClient
//启用Feign
@EnableFeignClients
//启用Hystrix
@EnableCircuitBreaker
//Application类一定要处于整个工程的根目录下，这样它才能根据配置去扫描子节点下的Spring的Bean
public class Application {

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

修改com.study.spring.cloud.weather.controller包下的CityController类：

package com.study.spring.cloud.weather.controller;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import com.study.spring.cloud.weather.service.CityClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

//用于处理rest请求的controller
@RestController
public class CityController {

	@Autowired
	private CityClient cityClient;

	@GetMapping("/cities")
	//启用断路器
	@HystrixCommand(fallbackMethod = "defaultCities")
	public String listCity() {
		//通过Feign客户端来查找
		String body=cityClient.listCity();
		return body;
	}

	public String defaultCities(){
		return "City Data Server is down!";
	}
	
}

修改application.properties配置文件：

#应用名称
spring.application.name=micro-weather-eureka-client-feign-hystrix

#注册服务器的URL
eureka.client.service-url.defaultZone=http://localhost:8761/eureka/

#请求服务时的超时时间
feign.client.config.feignName.connect-timeout=5000

#读数据时的超时时间
feign.client.config.feignName.read-timeout=5000

运行

先在IDE上运行micro-weather-eureka-server

再通过命令行指定端口（如8085）运行msa-weather-city-eureka

最后在IDE上运行micro-weather-eureka-client-feign-hystrix

访问http://localhost:8080/cities页面：

将msa-weather-city-eureka断掉，再刷新http://localhost:8080/cities页面：

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