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詳解spring cloud hystrix緩存功能的使用

更新時間：2018年08月18日 10:02:37 作者：TS笑天

這篇文章主要介紹了詳解spring cloudhystrix緩存功能的使用，小編覺得挺不錯的，現(xiàn)在分享給大家，也給大家做個參考。一起跟隨小編過來看看吧

hystrix緩存的作用是

- 1.減少重復(fù)的請求數(shù)，降低依賴服務(wù)的返回數(shù)據(jù)始終保持一致。
- 2.==在同一個用戶請求的上下文中，相同依賴服務(wù)的返回數(shù)據(jù)始終保持一致==。
- 3.請求緩存在run()和construct()執(zhí)行之前生效，所以可以有效減少不必要的線程開銷。

1 通過HystrixCommand類實現(xiàn)

1.1 開啟緩存功能

繼承HystrixCommand或HystrixObservableCommand，覆蓋getCacheKey()方法，指定緩存的key，開啟緩存配置。

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("調(diào)用失敗");
    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

通過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中的緩存是不共享的，還有這個request內(nèi)部一個ThreadLocal，所以request只能限于當(dāng)前線程。

1.3 清除失效緩存

繼承HystrixCommand或HystrixObservableCommand，在更新接口調(diào)用完成后，清空緩存。

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("調(diào)用失敗");
//    return user;
//  }

  @Override
  protected String getCacheKey() {
    return user.getUsername();
  }
}

2 使用@CacheResult、@CacheRemove和@CacheKey標(biāo)注來實現(xiàn)緩存

2.1 使用@CacheResult實現(xiàn)緩存功能

  @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用來標(biāo)示緩存key(cacheKey)的生成函數(shù)。函數(shù)的名稱可任意取名，入?yún)⒑蜆?biāo)注@CacheResult的方法是一致的，返回類型是String。

2.2 使用@CacheResult和@CacheKey實現(xiàn)緩存功能

  @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();
  }

標(biāo)注@HystrixCommand注解的方法，使用@CacheKey標(biāo)注需要指定的參數(shù)作為緩存key。

2.3 使用@CacheRemove清空緩存

  @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必須指定commandKey，否則程序無法找到緩存位置。

以上就是本文的全部內(nèi)容，希望對大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。

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