Spring Cloud（5）：Hystrix的使用

熔断：类似生活中的保险丝，电流过大就会熔断

降级：类似生活中的旅行，行李箱只有那么大，所以要抛弃一些非必需的物品

熔断降级应用：

某宝双十一商品下单，用户量巨大，于是考虑抛弃相关商品推荐等模块，确保该商品信息和下单功能通畅

熔断和降级的区别以及联系：

1.两者都是为了防止系统崩溃，提高可用性

2.最终给用户的体验是某些功能暂时不可用

3.服务熔断一般是由下游服务故障导致的，服务降级一般是从系统整体负荷考虑，由调用方控制

Hystrix的使用：

基于上一篇Feign的使用：https://www.cnblogs.com/xuyiqing/p/10869026.html

订单服务Order-Service中加入依赖

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

在启动类中加入注解

package org.dreamtech.orderservice;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;

import org.springframework.cloud.openfeign.EnableFeignClients;
import org.springframework.cloud.openfeign.ribbon.LoadBalancerFeignClient;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

@SpringBootApplication
@EnableFeignClients
@EnableCircuitBreaker
public class OrderServiceApplication {

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

    @Bean
    @LoadBalanced
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }
}

Controller层进行修改

package org.dreamtech.orderservice.controller;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import org.dreamtech.orderservice.service.ProductOrderService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

import java.util.HashMap;
import java.util.Map;

@RestController
@RequestMapping("/api/order")
public class OrderController {
    private final ProductOrderService productOrderService;

    @Autowired
    public OrderController(ProductOrderService productOrderService) {
        this.productOrderService = productOrderService;
    }

    @RequestMapping("/save")
    @HystrixCommand(fallbackMethod = "saveOrderFail")
    public Object save(@RequestParam("user_id") int userId, @RequestParam("product_id") int productId) {
        Map<String, Object> data = new HashMap<>();
        data.put("code", 0);
        data.put("data", productOrderService.save(userId, productId));
        return data;
    }

    private Object saveOrderFail(int userId, int productId) {
        Map<String, Object> msg = new HashMap<>();
        msg.put("code", -1);
        msg.put("msg", "请稍后重试");
        return msg;
    }
}

注意：saveOrderFail方法的参数必须和save的参数一致

依次启动Eureka-Server->Product-Service->Order-Service

访问：http://localhost:8781/api/order/save?user_id=1&product_id=4

正常显示：

{"code":0,"data":{"id":0,"productName":"\"iPhone4 data from port=8771\"","tradeNo":"13933d59-34fd-473a-8dbe-f114bc9fd2b9","price":4444,"createTime":"2019-05-17T03:54:12.682+0000","userId":1,"userName":null}}

这时候我关闭Product-Service，模拟熔断

再次访问：http://localhost:8781/api/order/save?user_id=1&product_id=4

显示：

{"msg":"请稍后重试","code":-1}

说明Hystrix配置和使用成功！

Feign结合Hystrix的使用：

配置Feign允许Hystrix

feign:
  hystrix:
    enabled: true

FeignClient加入fallback处理

package org.dreamtech.orderservice.service;

import org.dreamtech.orderservice.fallback.ProductClientFallback;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;

@FeignClient(name = "product-service",fallback = ProductClientFallback.class)
public interface ProductClient {
    @RequestMapping("/api/product/find")
    String findById(@RequestParam(value = "id")int id);
}

ProductClientFallback

package org.dreamtech.orderservice.fallback;

import org.dreamtech.orderservice.service.ProductClient;
import org.springframework.stereotype.Component;

@Component
public class ProductClientFallback implements ProductClient {
    @Override
    public String findById(int id) {
        System.out.println("Feign调用Product-Service异常");
        return null;
    }
}

启动项目，访问：http://localhost:8781/api/order/save?user_id=1&product_id=3成功

关闭Product-Service，访问http://localhost:8781/api/order/save?user_id=1&product_id=3

显示

{"msg":"请稍后重试","code":-1}

并且在控制台打印

Feign调用Product-Service异常

服务异常报警通知：

只是熔断和降级是不够了，还需要报警机制

由于访问量较大，要做到只报警一次，那么需要进行标识

通常实现原理基于缓存，比如Redis

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-redis</artifactId>
        </dependency>

配置

spring:
  application:
    name: order-service
  redis:
    host: 127.0.0.1
    database: 0
    port: 6379
    timeout: 2000

代码

package org.dreamtech.orderservice.controller;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import org.apache.commons.lang.StringUtils;
import org.dreamtech.orderservice.service.ProductOrderService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;

@RestController
@RequestMapping("/api/order")
public class OrderController {
    private final ProductOrderService productOrderService;

    private final StringRedisTemplate redisTemplate;

    @Autowired
    public OrderController(ProductOrderService productOrderService, StringRedisTemplate redisTemplate) {
        this.productOrderService = productOrderService;
        this.redisTemplate = redisTemplate;
    }

    @RequestMapping("/save")
    @HystrixCommand(fallbackMethod = "saveOrderFail")
    public Object save(@RequestParam("user_id") int userId, @RequestParam("product_id") int productId) {
        Map<String, Object> data = new HashMap<>();
        data.put("code", 0);
        data.put("data", productOrderService.save(userId, productId));
        return data;
    }

    private Object saveOrderFail(int userId, int productId) {

        String saveOrderKey = "save-order";
        String sendValue = redisTemplate.opsForValue().get(saveOrderKey);

        new Thread(() -> {
            if (StringUtils.isBlank(sendValue)) {
                // TODO 由于没有短信发送接口，模拟发送短信
                System.out.println("短信发送成功");
                redisTemplate.opsForValue().set(saveOrderKey, "save-order-fail", 20, TimeUnit.SECONDS);
            } else {
                System.out.println("已经发送过短信，20秒内不重复发送");
            }
        }).start();

        Map<String, Object> msg = new HashMap<>();
        msg.put("code", -1);
        msg.put("msg", "请稍后重试");
        return msg;
    }
}

测试

启动项目，访问http://localhost:8781/api/order/save?user_id=1&product_id=3没有问题

关闭Product-Service再访问，控制台打印：

Feign调用Product-Service异常
短信发送成功

再次访问：

Feign调用Product-Service异常
已经发送过短信，20秒内不重复发送

等待20秒访问：

Feign调用Product-Service异常
短信发送成功

成功

或者更进一步，拿到IP，发送短信

package org.dreamtech.orderservice.controller;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import org.apache.commons.lang.StringUtils;
import org.dreamtech.orderservice.service.ProductOrderService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

import javax.servlet.http.HttpServletRequest;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;

@RestController
@RequestMapping("/api/order")
public class OrderController {
    private final ProductOrderService productOrderService;

    private final StringRedisTemplate redisTemplate;

    @Autowired
    public OrderController(ProductOrderService productOrderService, StringRedisTemplate redisTemplate) {
        this.productOrderService = productOrderService;
        this.redisTemplate = redisTemplate;
    }

    @RequestMapping("/save")
    @HystrixCommand(fallbackMethod = "saveOrderFail")
    public Object save(@RequestParam("user_id") int userId, @RequestParam("product_id") int productId, HttpServletRequest request) {
        Map<String, Object> data = new HashMap<>();
        data.put("code", 0);
        data.put("data", productOrderService.save(userId, productId));
        return data;
    }

    private Object saveOrderFail(int userId, int productId,HttpServletRequest request) {

        String saveOrderKey = "save-order";
        String sendValue = redisTemplate.opsForValue().get(saveOrderKey);
        String ip = request.getRemoteAddr();

        new Thread(() -> {
            if (StringUtils.isBlank(sendValue)) {
                // TODO 由于没有短信发送接口，模拟发送短信
                System.out.println("短信发送成功，紧急情况，用户下单失败！来自于IP："+ip);
                redisTemplate.opsForValue().set(saveOrderKey, "save-order-fail", 20, TimeUnit.SECONDS);
            } else {
                System.out.println("已经发送过短信，20秒内不重复发送");
            }
        }).start();

        Map<String, Object> msg = new HashMap<>();
        msg.put("code", -1);
        msg.put("msg", "请稍后重试");
        return msg;
    }
}

Hystrix自定义配置：

关闭超时时间（实际情况不要用）

hystrix:
  command:
    default:
      execution:
        timeout:
          enabled: false

修改超时时间为4秒：

hystrix:
  command:
    default:
      execution:
        isolation:
          thread:
            timeoutInMilliseconds: 4000

不过Feign默认超时时间少于4秒，所以对Feign也进行修改：

feign:
  hystrix:
    enabled: true
  client:
    config:
      default:
        connectTimeout: 4000
        readTimeout: 4000

感觉YML的配置真的不舒服，不如继续用PROPERTIES

Hystrix-Dashboard：对Hystrix过程和结果的可视化界面

Hystrix-Dashboard的使用：

加入依赖：不只是Dashboard，还依赖于SpringBoot的监控Actuator

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-hystrix-dashboard</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>

在启动类中加入注解：@EnableHystrixDashboard

package org.dreamtech.orderservice;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.cloud.netflix.hystrix.dashboard.EnableHystrixDashboard;
import org.springframework.cloud.openfeign.EnableFeignClients;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

@SpringBootApplication
@EnableFeignClients
@EnableCircuitBreaker
@EnableHystrixDashboard
public class OrderServiceApplication {

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

    @Bean
    @LoadBalanced
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }
}

启动后访问：http://localhost:8781/hystrix

根据提示输入http://localhost:8781/actuator/hystrix.stream，发现报错：

Unable to connect to Command Metric Stream.

而且我如我直接访问http://localhost:8781/actuator/hystrix.stream也会显示404

解决：配置文件

management:
  endpoints:
    web:
      exposure:
        include: "*"

原因：配置Actuator开启全部端点

启动后访问：http://localhost:8781/hystrix

根据提示输入http://localhost:8781/actuator/hystrix.stream

或者直接访问：http://localhost:8781/actuator/hystrix.stream不会报错