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。

hystrix缓存功能的使用