SpringCloud之Hystrix的详细使用

1.概念

服务降级：服务器繁忙，请稍后再试，不让客户端等待，并立即返回一个友好的提示（一般发生在 程序异常，超时，服务熔断触发服务降级，线程池、信号量 打满也会导致服务降级）
服务熔断 ： 达到最大服务访问后，直接拒绝访问，然后调用服务降级的方法并返回友好提示（如保险丝一样）
服务限流 ： 秒杀等高并发操作，严禁一窝蜂的过来拥挤，排队进入，一秒钟n个，有序进行

***一.服务降级***

2.不使用hystrix的项目

大致的service和controller层如下

***************controller*****************
package com.sky.springcloud.controller;

import com.sky.springcloud.service.paymentservice;
import lombok.extern.slf4j.slf4j;
import org.springframework.beans.factory.annotation.value;
import org.springframework.web.bind.annotation.getmapping;
import org.springframework.web.bind.annotation.pathvariable;
import org.springframework.web.bind.annotation.restcontroller;
import javax.annotation.resource;
@restcontroller
@slf4j
public class paymentcontroller {
    @resource
    private paymentservice paymentservice;
    @value("${server.port}")
    private string serverport;
    @getmapping("/payment/hystrix/ok/{id}")
    public string paymentinfo_ok(@pathvariable("id") integer id){
        string result = paymentservice.paymentinfo_ok(id);
        log.info("*****"+ result);
        return result;
    }
    @getmapping("/payment/hystrix/timeout/{id}")
    public string paymentinfo_timeout(@pathvariable("id") integer id){
        string result = paymentservice.payment_info_timeout(id);
}
*******************service******************** 
package com.sky.springcloud.service;
import org.springframework.stereotype.service;
import java.util.concurrent.timeunit;
@service
public class paymentserviceimpl implements paymentservice{
    @override
    public string paymentinfo_ok(integer id) {
        return "线程池：" + thread.currentthread().getname() + "paymentinfo_ok. id:" + id + "\t" + "~~~~~";
    public string payment_info_timeout(integer id) {
       try {
            timeunit.seconds.sleep(5);
        } catch (interruptedexception e) {
            e.printstacktrace();
        }
        return "线程池：" + thread.currentthread().getname() + "paymentinfo_timeout. id:" + id + "\t" + "~~~~~";

在这种情况时,当通过浏览器访问 timeout这个方法,会三秒后返回结果,而当访问 ok 这个方法时,会直接返回结果(但是这是在访问量很少的时候,一旦访问量过多,访问ok时也会出现延迟,这里可以使用jmeter模拟两万个访问量,如下)

使用 jmeter 模拟后,再去访问ok,会明显出现加载的效果

3. 使用hystrix

在主启动类添加注解
@enablehystrix

package com.sky.springcloud;

import org.springframework.boot.springapplication;
import org.springframework.boot.autoconfigure.springbootapplication;
import org.springframework.cloud.netflix.eureka.enableeurekaclient;
import org.springframework.cloud.netflix.hystrix.enablehystrix;
@springbootapplication
@enableeurekaclient //启用eureka
@enablehystrix     //启用hystrix
public class payment8001 {
    public static void main(string[] args) {
        springapplication.run(payment8001.class,args);
    }
}

在原有的基础上,在service层加上如下注解

 @hystrixcommand(fallbackmethod = "payment_info_timeouthandler",//当服务降级时,调用payment_info_timeouthandler方法
                  commandproperties = {
            @hystrixproperty(name = "execution.isolation.thread.timeoutinmilliseconds",
            value = "3000")//设置时间为3秒,超过三秒就为时间超限

*****************改后的service*******************
package com.sky.springcloud.service;

import com.netflix.hystrix.contrib.javanica.annotation.hystrixcommand;
import com.netflix.hystrix.contrib.javanica.annotation.hystrixproperty;
import org.springframework.stereotype.service;

import java.util.concurrent.timeunit;
@service
public class paymentserviceimpl implements paymentservice{
    @override
    public string paymentinfo_ok(integer id) {
        return "线程池：" + thread.currentthread().getname() + "paymentinfo_ok. id:" + id + "\t" + "~~~~~";
    }

    @hystrixcommand(fallbackmethod = "payment_info_timeouthandler",commandproperties = {
            @hystrixproperty(name = "execution.isolation.thread.timeoutinmilliseconds",value = "3000")
    })
    public string payment_info_timeout(integer id) {
      try {
            timeunit.seconds.sleep(5);
        } catch (interruptedexception e) {
            e.printstacktrace();
        }
      // int a = 10 / 0;
        return "线程池：" + thread.currentthread().getname() + "paymentinfo_timeout. id:" + id + "\t" + "~~~~~";
    }
    public string payment_info_timeouthandler(integer id){
        return "线程超时或异常 " + thread.currentthread().getname();
    }
}

如上service所示,如果再次访问timeout需要等待五秒,但是hystrix设置的超时时间为三秒,所以当三秒后没有结果就会服务降级,从而调用timeouthandler这个指定 的方法来执行(或者有程序出错等情况也会服务降级)

4. 全局的hystrix配置

@defaultproperties(defaultfallback = “gloub_test”)

package com.sky.springcloud.service;

import com.netflix.hystrix.contrib.javanica.annotation.defaultproperties;
import com.netflix.hystrix.contrib.javanica.annotation.hystrixcommand;
import com.netflix.hystrix.contrib.javanica.annotation.hystrixproperty;
import org.springframework.stereotype.service;
@service
@defaultproperties(defaultfallback = "gloub_test")
public class paymentserviceimpl implements paymentservice{
    @override
    @hystrixcommand
    public string paymentinfo_ok(integer id) {
        int a = 10 / 0;
        return "线程池：" + thread.currentthread().getname() + "paymentinfo_ok. id:" + id + "\t" + "~~~~~";
    }
    @hystrixcommand(fallbackmethod = "payment_info_timeouthandler",commandproperties = {
            @hystrixproperty(name = "execution.isolation.thread.timeoutinmilliseconds",value = "3000")
    })
    public string payment_info_timeout(integer id) {
   /*     try {
            timeunit.seconds.sleep(5);
        } catch (interruptedexception e) {
            e.printstacktrace();
        }*/
        return "线程池：" + thread.currentthread().getname() + "paymentinfo_timeout. id:" + id + "\t" + "~~~~~";
    public string payment_info_timeouthandler(integer id){
        return "线程超时或异常 " + thread.currentthread().getname();
    public string gloub_test(){
        return "走了全局的";
}

如上service所示,加了@hystrixcommand的方法里,
如果没指定fallbackmethod 就会默认去找全局的defaultfallback
这里 当paymentinfo_ok 方法出错时,会调用gloub_test方法
当payment_info_timeout出错时,会调用payment_info_timeouthandler方法

 ***二.服务熔断***

1.熔断机制概述

熔断机制是应对雪崩效应的一种微服务链路保护机制,当扇出链路的某个微服务出错不可用或者响应时间太长,会进行服务的降级,进而熔断该节点微服务的调用,快速返回错误的相应信息.当检测到该节点微服务调用相应正常后,恢复调用链路.

2.项目中使用

在上面的基础上,改写service和controller(添加以下代码)

//是否开启服务熔断(断路器)
 @hystrixproperty(name = "circuitbreaker.enabled",value = "true"),
 //服务请求的次数 
 @hystrixproperty(name = "circuitbreaker.requestvolumethreshold",value = "10"),
 //时间的窗口期
 @hystrixproperty(name = "circuitbreaker.sleepwindowinmilliseconds", value = "10000"),
 //当失败率达到多少后发生熔断
 @hystrixproperty(name = "circuitbreaker.errorthresholdpercentage",value = "60"), 

******************service*****************
    @hystrixcommand(fallbackmethod = "paymentcircuitbreaker_fallback",
                    commandproperties = {
                    @hystrixproperty(name = "circuitbreaker.enabled",value = "true"),
                    @hystrixproperty(name = "circuitbreaker.requestvolumethreshold",value = "10"),
                    @hystrixproperty(name = "circuitbreaker.sleepwindowinmilliseconds", value = "10000"),
                    @hystrixproperty(name = "circuitbreaker.errorthresholdpercentage",value = "60"),
                    })
    public string paymentcircuitbreaker(@pathvariable("id") integer id){
        if(id<0){
            throw new runtimeexception("********** id不能为负");
        }
        string serialnumber = idutil.simpleuuid();
        return thread.currentthread().getname() + "\t" + serialnumber;
    }
    public string paymentcircuitbreaker_fallback(@pathvariable("id") integer id){
        return  "id 不能为负:" + id;
************controller********************
    @getmapping("/payment/circuit/{id}")
        string result = paymentservice.paymentcircuitbreaker(id);
        log.info(result + "***********");
        return result;

如上所示,当访问paymentcircuitbreaker时,如果id小于零则会有一个运行错误,这时候就会通过服务降级来调用paymentcircuitbreaker_fallback方法,当错误的次数达到60%的时候(自己设的),就会出现服务熔断,这个时候再访问id大于零的情况,也会发生服务降级,因为开起了服务熔断,需要慢慢的恢复正常.

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