java nio and ByteBuffer problem

Question

I met a problem. I use nio socket to receive message. Upon a complete message is received, I send the dataBuffer which holds the received message to another user. But there is exception below. Where is the problem? I try to call dataBuffer.duplicate() and write it out. But at the receiver side, the read operation throws such exception. I have to assign a new ByteBuffer and make a new copy of message and write it out. In this case, there is no error. But I do not want the copy step. Is there any other way to solve it?

Exception thrown

java.nio.BufferOverflowException
    at java.nio.HeapByteBuffer.put(Unknown Source)
    at java.nio.ByteBuffer.put(Unknown Source)
    at serviceHandlerPackage.ServiceHandler.readComplete(ServiceHandler.java:218)

Code

readEventHAndler(SocketChannel socket) {
   readCompleteData(socket);
}

readCompleteData(Socket) {
    ByteBuffer dataBuffer; //hold complete message
    if(!dataComplete)  return;
    else   process(dataBuffer);
}

process(dataBuffer) {
   ...

   processHandler();

   sendNext(dataBuffer);

}


sendNext(dataBuffer) {
    write(dataBuffer);

}

Answer 1

Whenever you read data into a buffer, if you want to write the buffer out another channel, you need to call: buffer.flip() before writing. You don't need to duplicate the buffer if you are writing on the same thread as you are reading.

Also - BufferOverflowException means you are putting more data into the buffer than its capacity. This sounds like a buffer is not getting buffer.clear() called to reset the position to zero.

There isn't enough code written above to diagnose exactly what the problem is.