Hystix熔斷解決雪崩問題

1.線程隔離，服務降級（服務的消費方做降級處理）

當服務繁忙時，如果服務出現異常，不是粗暴的直接報錯，而是返回一個友好的提示，雖然拒絕了用戶的訪問，但是會返回一個結果。

這就好比去買魚，平常超市買魚會額外贈送殺魚的服務。等到逢年過節，超時繁忙時，可能就不提供殺魚服務了，這就是服務的降級。

系統特別繁忙時，一些次要服務暫時中斷，優先保證主要服務的暢通，一切資源優先讓給主要服務來使用，在雙十一、618時，京東天貓都會采用這樣的策略。

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 //服務的熔斷
@SpringCloudApplication  //SpringCloudApplication可以替代上面三個
public class UserConsumerDemoApplication {

    @Bean
    @LoadBalanced  //負載均衡
    public RestTemplate restTemplate() {
        // 這次我們使用了OkHttp客戶端,只需要注入工廠即可
        return new RestTemplate(new OkHttp3ClientHttpRequestFactory());
    }

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

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?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 {@Autowiredprivate RestTemplate restTemplate;@GetMapping("{id}")@HystrixCommand(fallbackMethod = "queryUserByIdFallback")   //單個方法的超時返回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 "用戶信息查詢出現異常！";
//        User user = new User();
//        user.setId(id);
//        user.setNickName("用戶信息查詢出現異常！");
//        return user;
    }
}

==========================
配置統一超時信息

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 "用戶信息查詢出現異常！";
//        User user = new User();
//        user.setId(id);
//        user.setNickName("用戶信息查詢出現異常！");
//        return user;
    //}

    public String queryUserByIdFallback(){
        return "用戶信息查詢出現異常！";
    }
}

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

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"),  //響應超時時間
            @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 "用戶信息查詢出現異常！";
    }
}

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