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。
