Reading to Process Freezes Console

Question

So, I've been working on a Java app that's supposed to let people run their Minecraft servers using a program with an interface. When you run a shell script, all output is put in the window, and then you can write input. The input is then read by the process and interpreted. This lets you use sub-commands, such as "start," "stop," "help," "op," and so on. However, I can't figure out how to send the input to the process.

This is what the console looks like:

I tried the following:

public void createConsoleInput(final InputStream inputStream /* Obtained via process.getInputStream() */)
{
    final Thread consoleThread = new Thread()
    {
        @Override
        public void run()
        {
            final BufferedReader br = new BufferedReader(new InputStreamReader(inputStream));
            consoleInput.addActionListener(new ActionListener()
            {
                @Override
                public void actionPerformed(ActionEvent e)
                {
                    try
                    {
                        String cmd = consoleInput.getText();
                        lastmessage = cmd;

                        System.out.println("» /" + cmd);
                        br.read(cmd.toCharArray());
                        consoleInput.setText("");
                    }
                    catch (IOException e1)
                    {
                        e1.printStackTrace();
                    }
                }
            });
        }
    };
    consoleThread.start();
}

The field, which I labeled "Input" in the above picture, when accelerated, will execute the actionPerformed() method. However, it seems to freeze at the line: br.read(cmd.toCharArray());

It unfreezes after the process is killed externally. It doesn't even do the System.out part until after it's been killed. So, my question is: how do I do this properly?

EDIT:

After changing it to a writer, it no longer hangs. Instead, it just prints the console message:

public void createConsoleInput(final BufferedWriter writer)
{
    final Thread consoleThread = new Thread()
    {
        @Override
        public void run()
        {
            consoleInput.addActionListener(new ActionListener()
            {
                @Override
                public void actionPerformed(ActionEvent e)
                {
                    try
                    {
                        String cmd = consoleInput.getText();
                        lastmessage = cmd;

                        System.out.println("» /" + cmd);
                        writer.write(cmd);
                        consoleInput.setText("");
                    }
                    catch (IOException e1)
                    {
                        e1.printStackTrace();
                    }
                }
            });
        }
    };
    consoleThread.start();
}

The writer is accessed like this:

BufferedWriter stdin = new BufferedWriter(new OutputStreamWriter(p.getOutputStream()));

EDIT 2: I've tried messing around with the code, but nothing seems to fix it. I feel like I'm just writing to the wrong stream.

An `InputStream` is something you can *read from* - it's input from *your* perspective (but it's output from the perspective of the other process) — user253751, Apr 30 '15 at 03:20
@immibis: Nope. Changing it to `writer.write(cmd + "\n");` didn't seem to change anything. — ColonelHedgehog, Apr 30 '15 at 03:55

score 0 · Answer 1 · answered Apr 30 '15 at 22:57

Fixed! I simply needed to flush the writer. Take a look:

public void createConsoleInput(final BufferedWriter writer)
{
    final Thread consoleThread = new Thread()
    {
        @Override
        public void run()
        {
            consoleInput.addActionListener(new ActionListener()
            {
                @Override
                public void actionPerformed(ActionEvent action)
                {
                    try
                    {
                        String cmd = consoleInput.getText();
                        lastmessage = cmd;

                        System.out.println("» /" + cmd);
                        writer.write(cmd + "\n");
                        consoleInput.setText("");
                        writer.flush();
                    }
                    catch (IOException e)
                    {
                        e.printStackTrace();
                    }
                }
            });
        }
    };
    consoleThread.start();
}

Reading to Process Freezes Console

1 Answers1