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。

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