Hystrix之服务降级代码演示

所有代码都在github上：https://github.com/demonruin/cloud2020/tree/master

服务降级就是指服务器忙，请稍候再试，不让客户端等待并立刻返回一个友好提示，fallback

哪些情况会触发降级：程序运行异常，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；

服务降级分为服务端降级和客户端降级，好比一双筷子，你可以夹肉，也可以夹菜，不过一般是用来在客户端降级使用，具体情况具体分析使用。下面分别举例在服务端降级和客户端降级代码演示。有个前提啊，就是项目中已经加入了Hystrix的包依赖支持，酌情选择添加

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

服务端降级

1、需要使用@HystrixCommand，设置兜底即fallback降级方法，设置拦截异常信息。8001服务正常timeout时间为6s，但是服务降级做了5秒等待限制，超过了就不再等待，进行服务降级，调用fallback方法；

package com.king.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;/*** created by king on 2020/4/16 3:22 下午*/
@Service
public class PaymentHystrixService {/*** 成功访问** @param id* @return*/public String getOk(Integer id) {return "线程池：" + Thread.currentThread().getName() + " ID:" + id + "\t 访问成功";}/*** 访问超时** @param id* @return* 5000是指5s*/@HystrixCommand(fallbackMethod ="paymentFallback_handler",commandProperties = {@HystrixProperty(name="execution.isolation.thread.timeoutInMilliseconds",value = "5000")})public String getTimeout(Integer id) {int timeout = 6;try {TimeUnit.SECONDS.sleep(timeout);} catch (InterruptedException e) {e.printStackTrace();}return "线程池：" + Thread.currentThread().getName() + " ID:" + id + "\t 访问超时，超时时间(秒)：" + timeout;}public String paymentFallback_handler(Integer id){return "线程池：" + Thread.currentThread().getName() + " paymentFallback_handler---ID:" + id + "\t ";}
}

2、主启动类加注解@EnableCircuitBreaker

package com.king.springcloud;import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;/*** created by king on 2020/4/16 3:21 下午*/
@SpringBootApplication
@EnableEurekaClient
@EnableCircuitBreaker
public class PaymentHystrixMain8001 {public static void main(String[] args) {SpringApplication.run(PaymentHystrixMain8001.class,args);}
}

3、测试结果展示

此时服务端的服务降级就完成代码演示开发了，下面介绍客户端服务降级演示

客户端服务降级

80订单微服务，也可以更好的保护自己，自己也依样画葫芦进行客户端降级保护。

服务降级，客户端去调用服务端，碰上服务端宕机或关闭，本次案例服务降级处理是在客户端80实现完成的，与服务端8001没有关系，只需要为Feign客户端定义的接口添加一个服务降级处理的实现类即可实现解耦；未来我们要面对的异常有：运行时异常比如1/0的异常，超时异常比如sleep(5)，宕机即服务端服务器宕机等等

1、首先需要配置yml，启动feign的hystrix支持

feign:hystrix:#如果处理自身的容错就开启。开启方式与生产端不一样。enabled: true

2、主启动类加上启用注解@EnableHystrix

package com.king.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;
import org.springframework.cloud.openfeign.EnableFeignClients;/*** created by king on 2020/4/16 5:39 下午*/
@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients
@EnableHystrix
public class OrderFeignHystrixMain80 {public static void main(String[] args) {SpringApplication.run(OrderFeignHystrixMain80.class,args);}
}

3、在controller接口上加注解，配置fallback降级兜底方法，进行请求超时等情况下的服务降级

package com.king.springcloud.controller;import com.king.springcloud.service.OrderFeignHystrixService;
import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import com.netflix.hystrix.contrib.javanica.annotation.HystrixProperty;
import lombok.extern.slf4j.Slf4j;
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;/*** created by king on 2020/4/16 5:43 下午*/
@RestController
@Slf4j
public class OrderFeignHystrixController {@Resourceprivate OrderFeignHystrixService orderFeignHystrixService;@GetMapping(value = "/payment/ok/{id}")public String getOK(@PathVariable("id") Integer id) {return orderFeignHystrixService.getOk(id);}@GetMapping(value = "/payment/timeout/{id}")@HystrixCommand(fallbackMethod = "fallbackHystrix_handler_order",commandProperties = {@HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds",value = "1500")})public String getTimeout(@PathVariable("id") Integer id) {return orderFeignHystrixService.getTimeout(id);}public String fallbackHystrix_handler_order(@PathVariable("id") Integer id){return "80请求服务失败";}
}

此处设置的请求超时时间为1500毫秒，而8001提供的服务超时时间是3000毫秒，所以客户端请求会直接请求超时，调用服务降级fallback方法，结果展示

上面是简单的服务降级举例，但是每个业务方法对应一个兜底的fallback方法，会造成代码膨胀。而降级fallback方法和业务代码混乱在一起，所以一般会进行处理，将统一和自定义的进行区分开，或者将fallback方法从业务代码中抽取出来；

统一和自定义分开：

一、在客户端服务降级，统一处理方式

在controller上加统一@DefaultProperties(defaultFallback = "globle_fallbackHystrix_handler")注解
在接口上统一加 @HystrixCommand注解
自定义的降级处理方法，扔参照timeout的接口自定义服务降级处理方法

package com.king.springcloud.controller;import com.king.springcloud.service.OrderFeignHystrixService;
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 lombok.extern.slf4j.Slf4j;
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;/*** created by king on 2020/4/16 5:43 下午*/
@RestController
@Slf4j
@DefaultProperties(defaultFallback = "globle_fallbackHystrix_handler")
public class OrderFeignHystrixController {@Resourceprivate OrderFeignHystrixService orderFeignHystrixService;@GetMapping(value = "/payment/ok/{id}")@HystrixCommandpublic String getOK(@PathVariable("id") Integer id) {return orderFeignHystrixService.getOk(id);}@GetMapping(value = "/payment/timeout/{id}")@HystrixCommand(fallbackMethod = "fallbackHystrix_handler_order",commandProperties = {@HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds",value = "1500")})public String getTimeout(@PathVariable("id") Integer id) {return orderFeignHystrixService.getTimeout(id);}public String fallbackHystrix_handler_order(@PathVariable("id") Integer id){return "80请求服务失败";}public String globle_fallbackHystrix_handler(){return "请求服务失败，返回全局服务降级处理方法";}
}

二、将降级方法从业务代码中抽取出来，不再糅合的处理方法

去掉上述方法中在controller上加统一@DefaultProperties(defaultFallback = "globle_fallbackHystrix_handler")注解
去掉在接口上统一加 @HystrixCommand注解
保留 yml中的feign启用hystrix的配置
新建FallbackServiceHandler类，实现接口OrderFeignHystrixService，并重写每一个方法，作为兜底fallback服务降级
在OrderFeignHystrixService的feign注解配置上，指定兜底fallback服务降级类

package com.king.springcloud.service;import org.springframework.stereotype.Component;/*** created by king on 2020/4/17 1:31 下午*/
@Component
public class FallbackServiceHandler implements OrderFeignHystrixService {public String getOk(Integer id) {return null;}public String getTimeout(Integer id) {return null;}
}

package com.king.springcloud.service;import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;/*** created by king on 2020/4/16 5:40 下午*/
@Component
@FeignClient(value = "CLOUD-PAYMENT-SERVICE-HYSTRIX",fallback = FallbackServiceHandler.class)
public interface OrderFeignHystrixService {@GetMapping(value = "/payment/ok/{id}")public String getOk(@PathVariable("id") Integer id);@GetMapping(value = "/payment/timeout/{id}")public String getTimeout(@PathVariable("id") Integer id);
}

测试结果如下