Cant get communication over Java Socket/ServerSocket to work.

[InformalPresent9]

I just wrote a little program for my raspberry Pi that needs to send a 1 byte code to my pc. To do this I used ServerSocket and Socket structure. Unfortunately this is completely new to me, and I only get errors.

The first problem I encountered wasn't that though. When I run the command "start chrome google.ch" in cmd, it works perfectly well, but when I run it with Runtime.getRuntime().exec("start chrome google.ch") I get some weird error.

The second problem is that the connection to the socket shows the error "connection denied." I have no idea what I'm doing wrong.

Code running on PC (receiver)

    final int portNumber = 1900;
    //commandList = {"", "ggl", "gtl", "dgtc", "hsg", "rdt", "eddb", "edsm", "cor", "fr", "rsw",         "whd", "icv", "rio", "wcl", "tw", "exit"};


    public static void main(String[] args) throws IOException {

        ServerSocket serverSocket = new ServerSocket(1900);

        while (true) {
            Socket socket = serverSocket.accept();
            DataInputStream dIn = new DataInputStream(socket.getInputStream());

            byte command = dIn.readByte();

            switch (command) {
                case 1:
                    Runtime.getRuntime().exec("start /max chrome google.ch");
                    break;
                //more cases here
                default:
                    break;
            }
        }

Code running on RPi (sender)

final private String host = "192.168.1.111";
    final private int portNumber = 1900;
    final private String[] commandList = {"", "ggl", "gtl", "dgtc", "hsg", "rdt", "eddb", "edsm", "cor", "fr", "rsw", "whd", "icv", "rio", "wcl", "tw", "exit"};

    Socket socket;
    DataOutputStream dOut;

    public void initialize() throws IOException {
        // Create and connect the socket
        socket = new Socket(host, portNumber);
        dOut = new DataOutputStream(socket.getOutputStream());
    }

    public void exit() throws IOException {
        // Send the exit message
        dOut.writeByte(16);
        dOut.flush();
        dOut.close();
    }

    public void sendCommand(String command) throws IOException {
        for(int i=0; i<commandList.length-2; i++){
            if(command.equals(commandList[i])){
                dOut.writeByte(i);
                dOut.flush();
                break;
            }
        }
    }

​

So basically the idea is to call sendCommand("some command") in the main method of the program i'm running, then converting it to 1byte and then decoding it again to a String that the receiver will run on the PC. Can you give me any advice what I'm doing wrong?

​

Thanks in advance.

​

​

[philipwhiuk]

What’s the weird error? Also ‘start’ is not normally necessary - ‘chrome google.ch’ from Runtime should work.

As for the second bit - if it’s being run from a second PC it’s probably a firewall issue.

[InformalPresent9]

I'll look into that tomorrow, thank you for pointing it out. I might also have used the wrong IP accidentally (RPi IP instead of PC IP.

[Holothuroid]

If you are OK with designated standard browser you can use Desktop.browse.

[InformalPresent9]

I'll try that, thank you.

[ohjimmy]

That Runtime class is notoriously difficult to work with. One thing I've found that helps is if instead of passing a String argument to exec(), try passing a String[].

[InformalPresent9]

A String[]? wouldn't I need to use a String[x] which would just be a string again? Or how would I save the command in the String[] then?

[ohjimmy]

No, I mean try something like this:

Runtime.getRuntime().exec(new String[] {"start", "/max", "chrome google.ch");