详解spring cloud hystrix缓存功能的使用

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 {

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 {

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(HystrixComsauqkIHcmmandGroupKey.Factory.asKey("userUpdateCacheCommand")));

this.restTemplate = restTemplate;

this.user = user;

}

@Override

protected UserVO run() throws Exception {

LOGGER.info("thread:" + Thread.currentThread().getName());

HttpEntity u = new HttpEntity(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 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 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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