java缓存实例

import  java.util.Collection;
import  java.util.Collections;
import  java.util.Iterator;
import  java.util.List;
import  java.util.Map;
import  java.util.concurrent.ConcurrentHashMap;

import  org.springframework.beans.factory.annotation.Autowired;
import  org.springframework.stereotype.Component;

import  net.blogjava.frankiegao123.log.slf4j.Log;
import  net.blogjava.frankiegao123.log.slf4j.LogFactory;

/**
 * <p>System.Config 配置缓存</p>
 *
 * @author frankiegao123
 * 2010-6-10 下午02:48:35
 */
@Component ( "configCache" )
public  class  ConfigCache  implements  ConfigService {

    private  final  static  Log log = LogFactory.getLog(ConfigCache. class );

    /**
     * 更新缓存时记录的时间
     */
    private  volatile  long  time = 0L;

    /**
     * 正在更新缓存时的门闩，为 true 时表示当前没有更新缓存，为 true 时表示当前正在更新缓存
     */
    private  volatile  boolean  updateGate =  true ;

    /**
     * 缓存容器
     */
    private  Map<String, SysConfig> cache =  new  ConcurrentHashMap<String, SysConfig>();

    private  CommonDao commonDao;

    @Autowired
    public  ConfigCache(CommonDao commonDao) {
        this .commonDao = commonDao;
        log.info( "initializing cache..." );
        refreshCache();
        time = System.currentTimeMillis();
        log.info( "initialized cache finished, cache size: {}, set cache time to current: {}, cache timeout: {}ms" , cache.size(), time, ConfigConstant.CACHE_TIMEOUT);
    }

    /**
     * <p>根据配置的键名获取配置值</p>
     *
     * @param configKey
     * @return
     * @author frankiegao123
     * 2010-6-10 上午11:18:33
     */
    public  SysConfig getSysConfig(String configKey) {
        long  current = System.currentTimeMillis();
        if (updateGate && isTimeout(current)) {
            synchronized  ( this ) {
                if (updateGate) {
                    timeoutSynRefresh(current);
                }
            }
        }
        return  cache.get(configKey);
    }

    /**
     * <p>超时时更新缓存。该方法需要在同步环境中调用</p>
     * @param current
     * @author frankiegao123
     * 2010-6-10 上午11:16:30
     */
    private  void  timeoutSynRefresh( long  current) {
        updateGate =  false ;
        log.info( "refresh cache start..., time out: {}, size: {}, set updateGate to false" , (current - time) /  1000.0 , cache.size());
        try  {
            refreshCache();
            time = current;
            log.info( "refresh cache finished, size after update: {}, set cache time to current: {}" , cache.size(), String.valueOf(time));
        }  catch  (Exception e) {
            log.error( "refresh cache failed" , e);
        }  finally  {
            updateGate =  true ;
            log.info( "refresh cache finished, set updateGate to true" );
        }
    }

    /**
     * <p>更新缓存数据</p>
     *
     * @author frankiegao123
     * 2010-6-10 上午11:15:55
     */
    private  void  refreshCache() {
        List<SysConfig> configs = commonDao.getSysConfigs();
        for (Iterator<SysConfig> i = configs.iterator(); i.hasNext(); ) {
            SysConfig config = i.next();
            cache.put(config.getKey(), config);
        }
        commonDao.clear();
        SysConfig config = cache.get(SysConfig.TEST_KEY);
        if (config ==  null ) {
            log.error( "refresh cache, cannot find TEST_KEY" );
        }  else  {
            log.info( "refresh cache, find TEST_KEY = [{}]" , config.getValue());
        }
    }

    /**
     * <p>缓存是否超时</p>
     *
     * @param current
     * @return
     * @author frankiegao123
     * 2010-6-10 上午11:16:12
     */
    private  boolean  isTimeout( long  current) {
        return  (current - time >= ConfigConstant.CACHE_TIMEOUT);
    }

    Collection<SysConfig> getSysConfigs() {
        return  Collections.unmodifiableCollection(cache.values());
    }

    int  getSize() {
        return  cache.size();
    }

    long  getTime() {
        return  time;
    }

    boolean  isUpdateGate() {
        return  updateGate;
    }

    void  refresh() {
        time = 0L;
        log.info( "refresh: reset cache time to 0" );
        getSysConfig( "none" );
        log.info( "refresh: refresh cache finished, cache: {0}" , String.valueOf(time));
    }
}