SpringCloud断路器Hystrix原理及用法解析

这篇文章主要介绍了SpringCloud断路器Hystrix原理及用法解析,文中通过示例代码介绍的非常详细，对大家的学习或者工作具有一定的参考学习价值,需要的朋友可以参考下

在分布式环境中，许多服务依赖项中的一些必然会失败。Hystrix是一个库，通过添加延迟容忍和容错逻辑，帮助你控制这些分布式服务之间的交互。Hystrix通过隔离服务之间的访问点、停止级联失败和提供回退选项来实现这一点，所有这些都可以提高系统的整体弹性

两个比较重要的类

• HystrixCommand
• HystrixObservableCommand

注解@HystrixCommand（fallbackMethods="methods"）methods中可以添加降级策略

除了提供服务降级

还提供了请求缓存

• @CacheResult
• @CacheRemve

不过添加CacheResult的时候，说

HystrixRequestContext未初始化。

2020-01-13 16:12:10.273 ERROR 15348 --- [nio-8083-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet]  : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.reflect.UndeclaredThrowableException] with root cause

java.lang.IllegalStateException: Request caching is not available. Maybe you need to initialize the HystrixRequestContext?
  at com.netflix.hystrix.HystrixRequestCache.get(HystrixRequestCache.java:104) ~[hystrix-core-1.5.18.jar:1.5.18]
  at com.netflix.hystrix.AbstractCommand$7.call(AbstractCommand.java:478) ~[hystrix-core-1.5.18.jar:1.5.18]
  at com.netflix.hystrix.AbstractCommand$7.call(AbstractCommand.java:454) ~[hystrix-core-1.5.18.jar:1.5.18]
  at rx.internal.operators.OnSubscribeDefer.call(OnSubscribeDefer.java:46) ~[rxjava-1.3.8.jar:1.3.8]
  at rx.internal.operators.OnSubscribeDefer.call(OnSubscribeDefer.java:35) ~[rxjava-1.3.8.jar:1.3.8]

查看官方文档https://github.com/Netflix/Hystrix/wiki/How-To-Use

Typically this context will be initialized and shut down via a ServletFilter that wraps a user request or some other lifecycle hook.

在同一用户请求的上下文中，相同依赖服务的返回数据始终保持一致。在当次请求内对同一个依赖进行重复调用，只会真实调用一次。在当次请求内数据可以保证一致性。

初始化是在filter中进行（官方建议），但是每一次请求都会进行初始化 。所以说和一般的缓存还是有去别的，可以解决高并发，保证的资源的线程安全。在某些场景很有用。

请求合并

  @HystrixCollapser(batchMethod = "findALl",collapserProperties = @HystrixProperty(name = "timerDelayInMilliseconds",value = "100"))
  public String doBFindOne(String id){

    System.out.println("begin do provider service");
    return restTemplate.getForEntity("http://service-provider:8081/api/v1/provider/do",String.class).getBody();
  }

全部代码

package com.gitee.munan56.cloud.hystrixconsumer;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCollapser;
import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import com.netflix.hystrix.contrib.javanica.annotation.HystrixProperty;
import com.netflix.hystrix.contrib.javanica.cache.annotation.CacheResult;
import com.netflix.hystrix.strategy.concurrency.HystrixRequestContext;
import com.netflix.ribbon.proxy.annotation.Hystrix;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;

import java.util.List;


@Service
public class AService {

  @Autowired
  private RestTemplate restTemplate;

  public String doAService(){
    return "A Service is run";
  }

//  @Hystrix(fallbackHandler = )
  @HystrixCommand(fallbackMethod = "error")
  public String doBServiceOne(){
    System.out.println("begin do provider service");
    return restTemplate.getForEntity("http://service-provider:8081/api/v1/provider/do",String.class).getBody();
  }

  
  @CacheResult(cacheKeyMethod = "getKey")
  @HystrixCommand(fallbackMethod = "error")
  public String doBServiceTwo(String id){

    System.out.println("begin do provider service");
    return restTemplate.getForEntity("http://service-provider:8081/api/v1/provider/do",String.class).getBody();
  }

  
  @HystrixCollapser(batchMethod = "findALl",collapserProperties = @HystrixProperty(name = "timerDelayInMilliseconds",value = "100"))
  public String doBFindOne(String id){

    System.out.println("begin do provider service");
    return restTemplate.getForEntity("http://service-provider:8081/api/v1/provider/do",String.class).getBody();
  }

  @HystrixCommand()
  public String findALl(List ids){
    System.out.println("begin do provider service");
    return restTemplate.getForEntity("http://service-provider:8081/api/v1/provider/do",String.class).getBody();
  }

  
  public String error(Throwable e){
    return "do provider error this is default result" + "the error is " + e.getMessage();
  }
  
  public String error(String id ,Throwable e){
    return "do provider error this is default result" + "the error is " + e.getMessage();
  }


  public String getKey(String id){
    return id;
  }
}

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