cassandra内部API使用二2010-07-07
/**根据Key和column从缓存读取数据.
*@paramaKeyAreaKey
*@paramaNamecolumn
*@returnObject缓存数据
*/
publicObjectget(StringaKeyArea,StringaName)
{
Map<String,Object>resultMap=getResultMap(aKeyArea,aName);
if(resultMap!=null)
{
returnresultMap.get(CacheConstants.CACHE_MAP_KEY_VALUE);
}
returnnull;
}
/**根据Key和column从缓存读取数据,包括timestamp.
*@paramaKeyAreaKey
*@paramaNamecolumn
*
*@returnMap<String,Object>缓存数据
*key:"cache.timestamp",value:存放缓存数据时的timestamp
*key:"cache.value",value:缓存对象
*/
publicMap<String,Object>getResultMap(StringaKeyArea,StringaName)
{
Map<String,Object>resultMap=newHashMap<String,Object>();
CassandraClientPoolpool=CassandraClientPoolFactory.INSTANCE.get();
//取得客户端（群集服务器）
CassandraClientclient=null;
try
{
//从群集服务器获得一个客户端
client=pool.borrowClient(mCassandraClient);
//Keyspace
Keyspacekeyspace=
client.getKeyspace(mDefaultKeyspace);
//ColumnPath
ColumnPathcolumnPath=newColumnPath(mDefaultColumnFamily);
columnPath.setColumn(bytes(aName));
//从缓存读取
Columncol=keyspace.getColumn(aKeyArea,columnPath);
byte[]objBytes=col.getValue();
//由微秒转换为毫秒
longtimestamp=col.getTimestamp()
/CacheConstants.MICROSECONDS_PER_MILLISECONDS;
//从字节数组获取对象
Objectobj=ByteUtil.getObjectFromBytes(objBytes);
//缓存对象
resultMap.put(CacheConstants.CACHE_MAP_KEY_VALUE,obj);
//存放缓存数据时的timestamp
resultMap.put(CacheConstants.CACHE_MAP_KEY_TIMESTAMP,timestamp);
//为确保finally中能正确释放client，此处需重获取一次
client=keyspace.getClient();
//用户的缓存数据
returnresultMap;
}
//Key或者Column不存在
catch(NotFoundExceptione)
{
sLog.error(e);
}
catch(Exceptione)
{
sLog.error("根据Key和column从缓存读取数据（包括timestamp）时出错。");
sLog.error(e);
}
finally
{
//finally中释放client
releaseClient(pool,client);
}
returnnull;
}