public void mark (int readAheadLimit) throws IOException

Marks the present position in the stream. Subsequent calls to reset() will attempt to reposition the stream to this point. Not all character-input streams support the mark() operation.

Parameters:
readAheadLimit    Limit on the number of characters that may be read while still preserving the mark. After reading this many characters, attempting to reset the stream may fail.

Exceptions:
IOException    If the stream does not support mark(), or if some other I/O error occurs