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package com.video.cache;

import java.util.concurrent.TimeUnit;

import org.apache.commons.lang.StringUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.ValueOperations;
import org.springframework.stereotype.Service;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.TypeReference;
/**
 * 双重检测防止缓存穿透模板方法
 * @author 张宇乐
 *
 */
@Service
public class CacheTemplate {
	
	@Autowired
	private RedisTemplate<String, String> redisTemplate;
	
	/**
	 * 
	 * @param key		缓存key
	 * @param clazz		返回值类型
	 * @param expire	缓存失效时间
	 * @param service   如果缓存查不到，调用持久层mapper查询数据
	 * @return
	 */
	public <T> T loadCache(String key, TypeReference<T> clazz, long expire,BaseServiceHandler<T> service) {
		
		//查询缓存（第一次检测缓存）
    	ValueOperations<String, String> ops = redisTemplate.opsForValue();
    	String json = ops.get(key);
    	
    	//判断是否为空
    	if(StringUtils.isNotEmpty(json) && !"null".equalsIgnoreCase(json)) {
    		return JSON.parseObject(json,clazz);
    	}
    	
    	synchronized (this) {
    		//第二次检测缓存
    		json = ops.get(key);
    		if(StringUtils.isNotEmpty(json) && !"null".equalsIgnoreCase(json)) {
        		return JSON.parseObject(json,clazz);
        	}
			
    		//查询DB
    		T result = service.load();
    		//重置缓存
    		ops.set(key, JSON.toJSONString(result), expire, TimeUnit.MINUTES);
    		return result;
		}
	}
	

}

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package com.video.cache;

/**
 * 持久层查询接口
 * 公共接口
 * @author 张宇乐
 *
 * @param <T>
 */
public interface BaseServiceHandler<T> {

	public T load();
}

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@Autowired
private UserDao userDao;

@Autowired
private CacheTemplate cacheTemplate;
    
//测试双重检测 -- 防止缓存穿透
@Override
public User getCacheUser(String userId) {
    User user = cacheTemplate.loadCache(Config.getLoginUserKey(userId), new TypeReference<User>() {}, 10, new BaseServiceHandler<User>() {
	    @Override
	    public User load() {
		    return userDao.selectByPrimaryKey(userId);
	    }
	});
    return user;
}

//测试双重检测 -- 防止缓存穿透
@Override
public List<User> getCacheUserList() {
	String key = "userList";
	return cacheTemplate.loadCache(key, new TypeReference<List<User>>() {}, 10, new BaseServiceHandler<List<User>>() {
		@Override
		public List<User> load() {
			return userDao.getAll();
		}
	});
}

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public User searchPhoto(@Param("userId") String userId);
    
@Select("select * from user;")
public List<User> getAll();