Custom java serialization of message

Question

Hi,

While writing a message on wire, I want to write down the number of bytes in the data followed by the data.

Message format:

{num of bytes in data}{data}

I can do this by writing the data to a temporary byteArrayOutput stream and then obtaining the byte array size from it, writing the size followed by the byte array. This approach involves a lot of overhead, viz. unnecessary creation of temporary byte arrays, creation of temporary streams, etc.

Do we have a better (considering both CPU and garbage creation) way of achieving this?

Answer 1

Here’s what I would do, in order of preference.

1. Don’t bother about memory consumption and stuff. Most likely this already is the optimal solution unless it takes a lot of time to create the byte representation of your data so that creating it twice is a noticable impact.
2. (Actually this would be more like #37 on my list, with #2 to #36 being empty.) Include a method in your all your data objects that can calculate the size of the byte representation and takes less resources than it would to create the byte representation.

Answer 2

A typical approach would be to introduce a re-useable ByteBuffer. For example:

ByteBuffer out = ...

int oldPos = out.position(); // Remember current position.
out.position(oldPos + 2); // Leave space for message length (unsigned short)

out.putInt(...); // Write out data.

// Finally prepend buffer with number of bytes.
out.putShort(oldPos, (short)(out.position() - (oldPos + 2)));

Once the buffer is populated you could then send the data over the wire using SocketChannel.write(ByteBuffer) (assuming you are using NIO).