Hystix熔断解决雪崩问题

1.线程隔离，服务降级（服务的消费方做降级处理）

当服务繁忙时，如果服务出现异常，不是粗暴的直接报错，而是返回一个友好的提示，虽然拒绝了用户的访问，但是会返回一个结果。

这就好比去买鱼，平常超市买鱼会额外赠送杀鱼的服务。等到逢年过节，超时繁忙时，可能就不提供杀鱼服务了，这就是服务的降级。

系统特别繁忙时，一些次要服务暂时中断，优先保证主要服务的畅通，一切资源优先让给主要服务来使用，在双十一、618时，京东天猫都会采用这样的策略。

pom.xml

<dependency>
    <groupid>org.springframework.cloud</groupid>
    <artifactid>spring-cloud-starter-netflix-hystrix</artifactid>
</dependency>

userconsumerapplication.java

package cn.itcast.user;

import org.springframework.boot.springapplication;
import org.springframework.boot.autoconfigure.springbootapplication;
import org.springframework.cloud.client.springcloudapplication;
import org.springframework.cloud.client.circuitbreaker.enablecircuitbreaker;
import org.springframework.cloud.client.discovery.enablediscoveryclient;
import org.springframework.cloud.client.loadbalancer.loadbalanced;
import org.springframework.context.annotation.bean;
import org.springframework.http.client.okhttp3clienthttprequestfactory;
import org.springframework.web.client.resttemplate;

//@enablediscoveryclient
//@springbootapplication
//@enablecircuitbreaker //服务的熔断
@springcloudapplication  //springcloudapplication可以替代上面三个
public class userconsumerdemoapplication {

    @bean
    @loadbalanced  //负载均衡
    public resttemplate resttemplate() {
        // 这次我们使用了okhttp客户端,只需要注入工厂即可
        return new resttemplate(new okhttp3clienthttprequestfactory());
    }

    public static void main(string[] args) {
        springapplication.run(userconsumerdemoapplication.class, args);
    }
}

 3.userhcontroller.java

package cn.itcast.user.controller;

import cn.itcast.user.pojo.user;
import com.netflix.hystrix.contrib.javanica.annotation.hystrixcommand;
import org.springframework.beans.factory.annotation.autowired;
import org.springframework.web.bind.annotation.getmapping;
import org.springframework.web.bind.annotation.pathvariable;
import org.springframework.web.bind.annotation.requestmapping;
import org.springframework.web.bind.annotation.restcontroller;
import org.springframework.web.client.resttemplate;

@restcontroller
@requestmapping("consumerh")
public class userhcontroller {
    @autowired
    private resttemplate resttemplate;

    @getmapping("{id}")
    @hystrixcommand(fallbackmethod = "queryuserbyidfallback")   //单个方法的超时返回
    public string queryuserbyid(@pathvariable("id") long id){
        string url = "http://user-service/user/" + id;
        //user user = resttemplate.getforobject(url, user.class);
        //return  user;
        string user = resttemplate.getforobject(url, string.class);
        return user;
    }

    public string queryuserbyidfallback(@pathvariable("id") long id){
        return "用户信息查询出现异常！";
//        user user = new user();
//        user.setid(id);
//        user.setnickname("用户信息查询出现异常！");
//        return user;
    }
}

==========================
配置统一超时信息

package cn.itcast.user.controller;

import cn.itcast.user.pojo.user;
import com.netflix.hystrix.contrib.javanica.annotation.defaultproperties;
import com.netflix.hystrix.contrib.javanica.annotation.hystrixcommand;
import org.springframework.beans.factory.annotation.autowired;
import org.springframework.web.bind.annotation.getmapping;
import org.springframework.web.bind.annotation.pathvariable;
import org.springframework.web.bind.annotation.requestmapping;
import org.springframework.web.bind.annotation.restcontroller;
import org.springframework.web.client.resttemplate;

@restcontroller
@requestmapping("consumerh")
@defaultproperties(defaultfallback = "queryuserbyidfallback")
public class userhcontroller {
    @autowired
    private resttemplate resttemplate;

    @getmapping("{id}")
    //@hystrixcommand(fallbackmethod = "queryuserbyidfallback")
    @hystrixcommand
    public string queryuserbyid(@pathvariable("id") long id){
        string url = "http://user-service/user/" + id;
        //user user = resttemplate.getforobject(url, user.class);
        //return  user;
        string user = resttemplate.getforobject(url, string.class);
        return user;
    }

    //public string queryuserbyidfallback(@pathvariable("id") long id){
        //return "用户信息查询出现异常！";
//        user user = new user();
//        user.setid(id);
//        user.setnickname("用户信息查询出现异常！");
//        return user;
    //}

    public string queryuserbyidfallback(){
        return "用户信息查询出现异常！";
    }
}

=============================================================

package cn.itcast.user.controller;

import cn.itcast.user.pojo.user;
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.beans.factory.annotation.autowired;
import org.springframework.web.bind.annotation.getmapping;
import org.springframework.web.bind.annotation.pathvariable;
import org.springframework.web.bind.annotation.requestmapping;
import org.springframework.web.bind.annotation.restcontroller;
import org.springframework.web.client.resttemplate;

@restcontroller
@requestmapping("consumerh")
@defaultproperties(defaultfallback = "queryuserbyidfallback")
public class userhcontroller {
    @autowired
    private resttemplate resttemplate;

    @getmapping("{id}")
    @hystrixcommand(commandproperties = {
            @hystrixproperty(name = "execution.isolation.thread.timeoutinmilliseconds",value = "3000"),  //响应超时时间
            @hystrixproperty(name = "circuitbreaker.requestvolumethreshold",value = "10"),
            @hystrixproperty(name = "circuitbreaker.sleepwindowinmilliseconds",value = "10000"),   
            @hystrixproperty(name = "circuitbreaker.errorthresholdpercentage",value = "60")
    })
    public string queryuserbyid(@pathvariable("id") long id){
        if(id % 2 ==0){
            throw new runtimeexception("");
        }
        string url = "http://user-service/user/" + id;
        string user = resttemplate.getforobject(url, string.class);
        return user;
    }

    public string queryuserbyidfallback(){
        return "用户信息查询出现异常！";
    }
}