详解spring cloud hystrix缓存功能的使用

hystrix缓存的作用是

- 1.减少重复的请求数，降低依赖服务的返回数据始终保持一致。
- 2.==在同一个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==。
- 3.请求缓存在run()和construct()执行之前生效，所以可以有效减少不必要的线程开销。

1 通过hystrixcommand类实现

1.1 开启缓存功能

继承hystrixcommand或hystrixobservablecommand，覆盖getcachekey()方法，指定缓存的key，开启缓存配置。

import com.netflix.hystrix.hystrixcommand;
import com.netflix.hystrix.hystrixcommandgroupkey;
import com.netflix.hystrix.hystrixcommandkey;
import com.netflix.hystrix.hystrixrequestcache;
import com.netflix.hystrix.strategy.concurrency.hystrixconcurrencystrategydefault;
import com.szss.demo.orders.vo.uservo;
import org.slf4j.logger;
import org.slf4j.loggerfactory;
import org.springframework.web.client.resttemplate;

public class usercachecommand extends hystrixcommand<uservo> {
  private static final logger logger = loggerfactory.getlogger(usercachecommand.class);

  private static final hystrixcommandkey getter_key= hystrixcommandkey.factory.askey("commandkey");
  private resttemplate resttemplate;
  private string username;

  public usercachecommand(resttemplate resttemplate, string username) {
    super(setter.withgroupkey(hystrixcommandgroupkey.factory.askey("usercachecommand")).andcommandkey(getter_key));
    this.resttemplate = resttemplate;
    this.username = username;
  }

  @override
  protected uservo run() throws exception {
    logger.info("thread:" + thread.currentthread().getname());
    return resttemplate.getforobject("http://users-service/user/name/{username}", uservo.class, username);
  }

  @override
  protected uservo getfallback() {
    uservo user = new uservo();
    user.setid(-1l);
    user.setusername("调用失败");
    return user;
  }

  @override
  protected string getcachekey() {
    return username;
  }

  public static void flushcache(string username){
    hystrixrequestcache.getinstance(getter_key, hystrixconcurrencystrategydefault.getinstance()).clear(username);
  }
}

1.2 配置hystrixrequestcontextservletfilter

通过servlet的filter配置hystrix的上下文。

import com.netflix.hystrix.strategy.concurrency.hystrixrequestcontext;
import javax.servlet.*;
import javax.servlet.annotation.webfilter;
import java.io.ioexception;

@webfilter(filtername = "hystrixrequestcontextservletfilter",urlpatterns = "/*",asyncsupported = true)
public class hystrixrequestcontextservletfilter implements filter {
  public void dofilter(servletrequest request, servletresponse response, filterchain chain) throws ioexception, servletexception {
    hystrixrequestcontext context = hystrixrequestcontext.initializecontext();
    try {
      chain.dofilter(request, response);
    } finally {
      context.shutdown();
    }
  }

  @override
  public void init(filterconfig filterconfig) throws servletexception {

  }

  @override
  public void destroy() {

  }
}

在不同context中的缓存是不共享的，还有这个request内部一个threadlocal，所以request只能限于当前线程。

1.3 清除失效缓存

继承hystrixcommand或hystrixobservablecommand，在更新接口调用完成后，清空缓存。

import com.netflix.hystrix.hystrixcommand;
import com.netflix.hystrix.hystrixcommandgroupkey;
import com.netflix.hystrix.hystrixcommandkey;
import com.szss.demo.orders.vo.uservo;
import org.slf4j.logger;
import org.slf4j.loggerfactory;
import org.springframework.http.httpentity;
import org.springframework.web.client.resttemplate;

public class userupdatecachecommand extends hystrixcommand<uservo> {
  private static final logger logger = loggerfactory.getlogger(userupdatecachecommand.class);

  private static final hystrixcommandkey getter_key = hystrixcommandkey.factory.askey("commandkey");
  private resttemplate resttemplate;
  private uservo user;

  public userupdatecachecommand(resttemplate resttemplate, uservo user) {
    super(setter.withgroupkey(hystrixcommandgroupkey.factory.askey("userupdatecachecommand")));
    this.resttemplate = resttemplate;
    this.user = user;
  }

  @override
  protected uservo run() throws exception {
    logger.info("thread:" + thread.currentthread().getname());
    httpentity<uservo> u = new httpentity<uservo>(user);
    uservo uservo=resttemplate.postforobject("http://users-service/user",u,uservo.class);
    usercachecommand.flushcache(user.getusername());
    return uservo;
  }

//  @override
//  protected uservo getfallback() {
//    uservo user = new uservo();
//    user.setid(-1l);
//    user.setusername("调用失败");
//    return user;
//  }

  @override
  protected string getcachekey() {
    return user.getusername();
  }
}

2 使用@cacheresult、@cacheremove和@cachekey标注来实现缓存

2.1 使用@cacheresult实现缓存功能

@cacheresult(cachekeymethod = "getcachekey")
@hystrixcommand(commandkey = "finduserbyid", groupkey = "userservice", threadpoolkey = "userservicethreadpool")
public uservo findbyid(long id) {
  responseentity<uservo> user = resttemplate.getforentity("http://users-service/user?id={id}", uservo.class, id);
  return user.getbody();
}

public string getcachekey(long id) {
  return string.valueof(id);
}

@cacheresult注解中的cachekeymethod用来标示缓存key(cachekey)的生成函数。函数的名称可任意取名，入参和标注@cacheresult的方法是一致的，返回类型是string。

2.2 使用@cacheresult和@cachekey实现缓存功能

@cacheresult
@hystrixcommand(commandkey = "finduserbyid", groupkey = "userservice", threadpoolkey = "userservicethreadpool")
public uservo findbyid2(@cachekey("id") long id) {
  responseentity<uservo> user = resttemplate.getforentity("http://users-service/user?id={id}", uservo.class, id);
  return user.getbody();
}

标注@hystrixcommand注解的方法，使用@cachekey标注需要指定的参数作为缓存key。

2.3 使用@cacheremove清空缓存

@cacheremove(commandkey = "finduserbyid")
@hystrixcommand(commandkey = "updateuser",groupkey = "userservice",threadpoolkey = "userservicethreadpool")
public void updateuser(@cachekey("id")uservo user){
  resttemplate.postforobject("http://users-service/user",user,uservo.class);
}

@cacheremove必须指定commandkey，否则程序无法找到缓存位置。

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持服务器之家。

原文链接：https://blog.csdn.net/zhuchuangang/article/details/74566185