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。