spring cloud：三、断路器（hystrix）

在分布式系统中，根据业务来拆分成一个个的微服务，服务与服务之间可以相互调用（RPC），在spring cloud 中可以用RestTemplate+ribbon和feign来调用。为了保证其高可用，单个服务有时候会集群部署，由于网络或程序自躾的原因，服务并不能保证百分百可靠可用，如果单个服务出现问题，调用这个服务就出现线程阻塞，此时若有大量的请求涌入，servlet容器的线程资源就会被消耗完毕导致服务瘫痪。服务与服务之间的依赖性，故障会传播，会对整个微服务系统造成不可估量的严重后果，这就是常说的服务故障的“雪崩效应”。为了解决这个问题，有人就提出了一种解决问题的思路，断路器模型。就是每一个调用服务的接口处加一个断路器，默认是关闭的，当对服务调用时，不可用的次数达到一个阀值时，断路器就会打开，通过回调方法迅速返回一个值结束调用，避免出现连锁故障。

一、改造上一篇文章的zhangsanService（ribbon+restTemplate方式），在pom.xml中加入hystrix的依赖

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

改造启动类ZhangsanServiceApplication.java:

package com.gaox.zhangsanService;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.netflix.hystrix.EnableHystrix;
import org.springframework.context.annotation.Bean;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

@SpringBootApplication
@EnableEurekaClient
@EnableHystrix
@RestController
public class ZhangsanServiceApplication {

   public static void main(String[] args) {
      SpringApplication.run(ZhangsanServiceApplication.class, args);
   }
   @Bean
   @LoadBalanced
   public RestTemplate restTemplate(){
      return new RestTemplate();
   }

   @Autowired
   private RestTemplate restTemplate;

   @RequestMapping("/hello")
   @HystrixCommand(fallbackMethod = "helloError")
   public String hello(String name){
      String result=restTemplate.getForObject("http://HELLOSERVICE/hello?name="+name,String.class);
      return result;

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

依次启动，serviceCenter,helloService:8762,helloService:8763,zhangsanService,在浏览器中访问http://localhost:8764/hello?name=zhangsan

浏览器依次会显示

你好，zhangsan。我是helloService,端口是8762

你好，zhangsan。我是helloService,端口是8763

此时关闭helloService:8763, http://localhost:8764/hello?name=zhangsan

浏览器依次会显示

你好，zhangsan。我是helloService,端口是8762

hello ,zhangsan! sorry ,error !

这说明当zhangsanService调用的服务helloService:8763不可用时，会执行快速失败，直接返回一个字符串，而不是等待响应超时，这就很好的控制了当大量请求涌入的时候线程不会阻塞

二、feign是自带断路器的，spring cloud的有些版本中，默认是关闭的，需要在配置文件中打开它，下面上一篇文章中的lisiService为基础来改造一下

Application.properties:

server.port=8765
spring.application.name=lisiService
eureka.client.service-url.defaultZone=http://localhost:8761/eureka/
feign.hystrix.enabled=true

LisiServiceApplication.java:

package com.gaox.lisiService;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.netflix.feign.EnableFeignClients;
import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients
@RestController
public class LisiServiceApplication {

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


    @FeignClient(value = "helloService" ,fallback = HelloError.class)
    public interface HelloService {
        @RequestMapping(value = "/hello", method = RequestMethod.GET)
         String hello(@RequestParam("name") String name);
    }
    @Component
    public class HelloError implements HelloService {
        @Override
        public String hello(String name){
            return "hello  ,"+name+"!  sorry ,error !";
        }
    }
    @Autowired
   private HelloService helloService;

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

依次启动serviceCenter,helloService:8762,helloService:8763,lisiService，然后在浏览器输入http://localhost:8765/hello?name=lisi，浏览器会交替显示

你好，lisi。我是helloService,端口是8762

你好，lisi。我是helloService,端口是8763

此时关闭helloService:8763, http://localhost:8764/hello?name=zhangsan

浏览器依次会显示

你好，lisi。我是helloService,端口是8762

hello , lisi! sorry ,error !

这说明断路器起作用了，当lisiService调用的服务helloService:8763不可用时，会执行快速失败，直接返回一个字符串，而不是等待响应超时，这就很好的控制了当大量请求涌入的时候线程不会阻塞

三、在feign中使用hystrix dashboard(仪表盘)功能

Pom.xml添加以下内容：

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

LisiServiceApplication.java启动类上加两个注解@EnableHystrixDashboard
和@EnableCircuitBreaker

package com.gaox.lisiService;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.netflix.feign.EnableFeignClients;
import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.cloud.netflix.hystrix.dashboard.EnableHystrixDashboard;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients
@RestController
@EnableHystrixDashboard
@EnableCircuitBreaker
publicclass LisiServiceApplication {

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

    @FeignClient(value = "helloService",fallback = HelloError.class)
    public interface HelloService{
        @RequestMapping(value = "/hello", method =RequestMethod.GET)
         String hello(@RequestParam("name") Stringname);
    }
    @Component
    public class HelloError implements HelloService{
        @Override
        public String hello(Stringname){
            return "hello ,"+name+"! sorry ,error !";
        }
    }
    @Autowired
   private HelloService helloService;

    @RequestMapping("/hello")
    public String hello(@RequestParam("name")Stringname){
    return helloService.hello(name);
    }
}

打开浏览器：访问http://localhost:8765/hystrix,界面如下：

第一个输入框：http://localhost:8765/hystrix.stream

Delay：默认不变即可

Title:（这个可以随便输入）

然后点击按钮进入，如图

四、在ribbon中使用hystrix dashboard(仪表盘)功能

Pom.xml添加以下内容：


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

LisiServiceApplication.java启动类上加个注解@EnableHystrixDashboard
package com.gaox.zhangsanService;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.netflix.hystrix.EnableHystrix;
import org.springframework.cloud.netflix.hystrix.dashboard.EnableHystrixDashboard;
import org.springframework.context.annotation.Bean;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

@SpringBootApplication
@EnableEurekaClient
@EnableHystrix
@EnableHystrixDashboard
@RestController
public class ZhangsanServiceApplication {

   public static void main(String[] args) {
      SpringApplication.run(ZhangsanServiceApplication.class, args);
   }
   @Bean
   @LoadBalanced
   public RestTemplate restTemplate(){
      return new RestTemplate();
   }

   @Autowired
   private RestTemplate restTemplate;

   @RequestMapping("/hello")
   @HystrixCommand(fallbackMethod = "helloError")
   public String hello(String name){
      String result=restTemplate.getForObject("http://HELLOSERVICE/hello?name="+name,String.class);
      return result;

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

然后打开浏览器之后的操作和上面feign方法的一样。

spring cloud：三、断路器（hystrix）

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