void open() throws java.io.IOException {
  if (source != null)   return;
  if (!channel.isOpen())   throw new IllegalStateException("Channel is closed");
  try {
    source=new ByteBufferRandomAccessSource(channel.map(FileChannel.MapMode.READ_ONLY,offset,length));
  }
 catch (  java.io.IOException e) {
    if (exceptionIsMapFailureException(e))     throw new MapFailedException(e);
    throw e;
  }
}

void open ( ) throws java . io . IOException { if ( source != null ) return ; if ( ! channel . isOpen ( ) ) throw new IllegalStateException ( "Channel is closed" ) ; try { source = new ByteBufferRandomAccessSource ( channel . map ( FileChannel . MapMode . READ_ONLY , offset , length ) ) ; } catch ( java . io . IOException e ) { if ( exceptionIsMapFailureException ( e ) ) throw new MapFailedException ( e ) ; throw e ; } }
map the region of the channel
