Question

I’m still a little shaky on using ByteBuffer‘s. What I want to do is have data written to the ByteBuffer, then go to the beginning of the ByteBuffer and write a byte before all of that data (the payload of a packet is written, then prepended with the header.) How can I do that?

Diagram:

Buffer starts with:

|  PAYLOAD  |

Buffer after op code header is added (after what I want to do):

|  HEADER  |  PAYLOAD  |

The | just being separators of the kind of data, not literally anything.

Answer 1

What you are looking for is called ‘scatter-gather I/O’ and it is supported by ScatteringByteChannel.read(ByteBuffer[]) and GatheringByteChannel.write(ByteBuffer[]). Note the arrays. These interfaces are supported by FileChannel, SocketChannel, and DatagramSocketChannel and the Pipe channels.