Thread: NIO UDP DatagramChannel data not sending out…

Nice to meet you, dear all.

I'm a beginner and this is my first time programming such thing using Java.

I'm writing a program which gets data input from a port, saves it into a buffer, and when the buffer is full, it'll send out the data using another port. The protocol is UDP.

So here is my code:

try {
    // UDP data-in settings
    DatagramChannel inChannel = DatagramChannel.open();
    SocketAddress inAddress = new InetSocketAddress(FMBuffer.IN_PORT);
    inChannel.bind(inAddress);
 
    // UDP data-out settings
    DatagramChannel outChannel = DatagramChannel.open();
    SocketAddress outAddress = new InetSocketAddress(FMBuffer.OUT_PORT);
    outChannel.bind(outAddress);
 
    LinkedList<ByteBuffer> buffer = new LinkedList<ByteBuffer>();
    ByteBuffer b = ByteBuffer
            .allocateDirect(FMBuffer.UDP_MAX_PACKET_SIZE);
 
    while (true) {          
 
        if (inChannel.receive(b) != null) { // Receive data and put into b
            b.flip();                   
            // Save b into the buffer
            buffer.addLast(b);
 
            System.out.print("In(" + buffer.size() + "): ");
            while (buffer.getLast().hasRemaining()) {                           
                System.out.write(buffer.getLast().get());
            }
            System.out.println();
 
            // If the buffer reaches the set limit
            if (buffer.size() > FMBuffer.BUFFER_LIST_SIZE) {
                // Send the first b out, then remove it
                System.out.print("Out(" + buffer.size() + "): ");
                while (buffer.getFirst().hasRemaining()) {                          
                    System.out.write(buffer.getFirst().get());
                    outChannel.send(buffer.getFirst(), outAddress);
                }
                System.out.println();
                buffer.removeFirst();
            }
 
            b.clear();
 
        } else { // Receive no data
            if (buffer.size() > 0) {
                // Send the first b out, then remove it
                System.out.print("Out remaining(" + buffer.size() + "): ");
                while (buffer.getFirst().hasRemaining()) {                          
                    System.out.write(buffer.getFirst().get());
                    outChannel.send(buffer.getFirst(), outAddress);
                }
                System.out.println();
                buffer.removeFirst();
            }
        }
    }
} catch (IOException e) {
    e.printStackTrace();
}

There are several problems...

I tried to use a program to read from 127.0.0.1:OUT_PORT. The program said that the port is in use. What shall I do?

Say BUFFER_LIST_SIZE = 5 and outChannel.send(...) is commented. The output data is always blank, not the input one. Also, if I stop sending data to it, it will not output the remaining data from its buffer. With inputs like "* UDP Flood. Server stress test ****", it will output:

 
    In(1): ***** UDP Flood. Server stress test ****
    In(2): ***** UDP Flood. Server stress test ****
    In(3): ***** UDP Flood. Server stress test ****
    In(4): ***** UDP Flood. Server stress test ****
    In(5): ***** UDP Flood. Server stress test ****
    In(6): ***** UDP Flood. Server stress test ****
    Out(6): 
    In(6): ***** UDP Flood. Server stress test ****
    Out(6): 
    In(6): ***** UDP Flood. Server stress test ****
    Out(6): 
    In(6): ***** UDP Flood. Server stress test ****
    Out(6):

Thank you so much!

Originally Posted by Norm

Has the program been executed more than once? Has the first execution stopped completely before the second one has started?

You mean the 3rd party test program that reads the OUT_PORT, or my Java program?
There is only one instance running at the same time.
Thank you so much.