Send byte array from java program to c++

Question

I am currently learning networking and need some help on figuring out the simplest way to send a byte array through UDP from a Java program to a C++ one. Previously, I created a very simple client and server program, both in Java, and was able to use the Java classes DatagramSocket and DatagramPacket to send and receive data packets between the two java client/server programs.

But now, I have a network emulator that I need to go through which is written in C++, so my fear is that it would not recognize the DatagramSocket and DatagramPacket data, since they are Java classes.

If I have the hostname and listening UDP port of the network emulator which is written in C++, how would I go about sending a byte array to it in Java?

robermann robermann · Accepted Answer · 2014-03-13T23:34:23

Your fear of Java classes not being recognized is wrong, because when you write UDP packets you are speaking a different API (UDP is a network protocol). You are not serializing Java objects.

Below there is a working example, a Java client sends UDP packets to a PureData (that is, a not-Java) server (from codesounding):

package codesounding;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;

/*
  Every instruction type triggers an UDP message, each on different ports:
            Variable declaration:   7001
            Start block ({):        7002
            End block (}):          7003
            break:                  7004
            continue:               7005
            do:                     7006
            for:                    7007
            if:                     7008
            return:                 7009
            throw:                  7010
            while:                  7011
 */
public class UDPProcessor extends SilentProcessor {
    private static final String TARGET = "target"; //target host name
    private final DatagramPacket packetVar;
    private final DatagramPacket packetStart;
    private final DatagramPacket packetEnd;
    private final DatagramPacket packetBreak;
    private final DatagramPacket packetContinue;
    private final DatagramPacket packetDo;
    private final DatagramPacket packetFor;
    private final DatagramPacket packetIf;
    private final DatagramPacket packetReturn;
    private final DatagramPacket packetThrow;
    private final DatagramPacket packetWhile;
    final DatagramSocket socket; 
    final byte[] signal = "1;\n".getBytes(); //this message will trigger both PureData and MaxMSP UDP receivers; see the example patches

    public UDPProcessor() {
        try {
            String target = "127.0.0.1";
            if (System.getProperty(TARGET) != null  && !System.getProperty(TARGET).equals("")) {
                target = System.getProperty(TARGET);
            }
            System.out.println("Sending to "+target+"...");
            socket = new DatagramSocket();
            InetAddress address = InetAddress.getByName(target);

            packetVar = new DatagramPacket(signal, signal.length, address, 7001);
            packetStart = new DatagramPacket(signal, signal.length, address, 7002);
            packetEnd = new DatagramPacket(signal, signal.length, address, 7003);
            packetBreak = new DatagramPacket(signal, signal.length, address, 7004);
            packetContinue = new DatagramPacket(signal, signal.length, address, 7005);
            packetDo = new DatagramPacket(signal, signal.length, address, 7006);
            packetFor = new DatagramPacket(signal, signal.length, address, 7007);
            packetIf = new DatagramPacket(signal, signal.length, address, 7008);
            packetReturn = new DatagramPacket(signal, signal.length, address, 7009);
            packetThrow = new DatagramPacket(signal, signal.length, address, 7010);
            packetWhile = new DatagramPacket(signal, signal.length, address, 7011);

        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    private synchronized void send(DatagramPacket packet) {
        try {
            socket.send(packet);
        } catch (IOException e) {
            e.printStackTrace();
            //skipping 
        }
    }

    public void getVarDeclaration() {
        send(packetVar);
    }

    public void getStartBlock() {
        send(packetStart);
    }

    public void getEndBlock() {
        send(packetEnd);
    }

    public void getIfStatement() {
        send(packetIf);
    }

    public void getForStatement() {
        send(packetFor);
    }

    public void getDoStatement() {
        send(packetDo);
    }

    public void getWhileStatement() {
        send(packetWhile);
    }

    public void getReturnStatement() {
        send(packetReturn);
    }

    public void getBreakStatement() {
        send(packetBreak);
    }

    public void getContinueStatement() {
        send(packetContinue);
    }

    public void getThrowStatement() {
        send(packetThrow);
    }

}

Send byte array from java program to c++

1 Answers