spring cloud：三、斷路器（hystrix）

在分佈式系統中，根據業務來拆分成一個個的微服務，服務與服務之間可以相互調用（RPC），在spring cloud 中可以用RestTemplate+ribbon和feign來調用。爲了保證其高可用，單個服務有時候會集羣部署，由於網絡或程序自躾的原因，服務並不能保證百分百可靠可用，如果單個服務出現問題，調用這個服務就出現線程阻塞，此時若有大量的請求涌入，servlet容器的線程資源就會被消耗完畢導致服務癱瘓。服務與服務之間的依賴性，故障會傳播，會對整個微服務系統造成不可估量的嚴重後果，這就是常說的服務故障的“雪崩效應”。爲了解決這個問題，有人就提出了一種解決問題的思路，斷路器模型。就是每一個調用服務的接口處加一個斷路器，默認是關閉的，當對服務調用時，不可用的次數達到一個閥值時，斷路器就會打開，通過回調方法迅速返回一個值結束調用，避免出現連鎖故障。

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

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

改造啓動類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 !";
   }
}

依次啓動，serviceCenter,helloService:8762,helloService:8763,zhangsanService,在瀏覽器中訪問http://localhost:8764/hello?name=zhangsan

瀏覽器依次會顯示

你好，zhangsan。我是helloService,端口是8762

你好，zhangsan。我是helloService,端口是8763

此時關閉helloService:8763, http://localhost:8764/hello?name=zhangsan

瀏覽器依次會顯示

你好，zhangsan。我是helloService,端口是8762

hello ,zhangsan! sorry ,error !

這說明當zhangsanService調用的服務helloService:8763不可用時，會執行快速失敗，直接返回一個字符串，而不是等待響應超時，這就很好的控制了當大量請求涌入的時候線程不會阻塞

二、feign是自帶斷路器的，spring cloud的有些版本中，默認是關閉的，需要在配置文件中打開它，下面上一篇文章中的lisiService爲基礎來改造一下

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);
    }
}

依次啓動serviceCenter,helloService:8762,helloService:8763,lisiService，然後在瀏覽器輸入http://localhost:8765/hello?name=lisi，瀏覽器會交替顯示

你好，lisi。我是helloService,端口是8762

你好，lisi。我是helloService,端口是8763

此時關閉helloService:8763, http://localhost:8764/hello?name=zhangsan

瀏覽器依次會顯示

你好，lisi。我是helloService,端口是8762

hello , lisi! sorry ,error !

這說明斷路器起作用了，當lisiService調用的服務helloService:8763不可用時，會執行快速失敗，直接返回一個字符串，而不是等待響應超時，這就很好的控制了當大量請求涌入的時候線程不會阻塞

三、在feign中使用hystrix dashboard(儀表盤)功能

Pom.xml添加以下內容：

<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啓動類上加兩個註解@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);
    }
}

打開瀏覽器：訪問http://localhost:8765/hystrix,界面如下：

第一個輸入框：http://localhost:8765/hystrix.stream

Delay：默認不變即可

Title:（這個可以隨便輸入）

然後點擊按鈕進入，如圖

四、在ribbon中使用hystrix dashboard(儀表盤)功能

Pom.xml添加以下內容：


<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啓動類上加個註解@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 !";
   }
}

然後打開瀏覽器之後的操作和上面feign方法的一樣。

spring cloud：三、斷路器（hystrix）

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