asyncExist

异步检查数据是否存在。

public static interface ExistListener extends GenericFutureListener<Future<Boolean>> {
    /**
     * This function will be called when listened asyncExist future is done.
     * @param future the listened future
     * @throws Exception
     *
     * Notice: User shouldn't do any operations that may block or time-consuming
     */
    @Override
    public void operationComplete(Future<Boolean> future) throws Exception;
}
 
/**
 * Check value existence for a specific (hashKey, sortKey) pair of current table, async version
 * @param hashKey used to decide which partition the key may exist
 *                if null or length == 0, means hash key is "".
 * @param sortKey all keys under the same hashKey will be sorted by sortKey
 *                if null or length == 0, means sort key is "".
 * @param timeout how long will the operation timeout in milliseconds.
 *                if timeout > 0, it is a timeout value for current op,
 *                else the timeout value in the configuration file will be used.
 *
 * @return A future for current op.
 *
 * Future return:
 *      On success: true if exist, false if not exist
 *      On failure: a throwable, which is an instance of PException
 *
 * Thread safety:
 *      The api is thread safe.
 *      All the listeners for the same table are guaranteed to be dispatched in the same thread, so all the
 *      listeners for the same future are guaranteed to be executed as the same order as the listeners added.
 *      But listeners for different tables are not guaranteed to be dispatched in the same thread.
 */
public Future<Boolean> asyncExist(byte[] hashKey, byte[] sortKey, int timeout/*ms*/);

注：

• 参数：需传入HashKey、SortKey、timeout。
  • timeout单位为毫秒，如果<=0，表示使用配置文件中的默认超时。
• 返回值：Future。
  • 返回结果是个布尔值。如果存在返回true，否则返回false。