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！";
    }
}