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From: Eric Sosman <esosman@comcast-dot-net.invalid>
Newsgroups: comp.lang.java.programmer
Subject: Re: Getting results of command execution
Date: Fri, 19 Jun 2015 11:01:01 -0400
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On 6/18/2015 10:30 AM, FredK wrote:
>
> The requirement is essentially that I want to include a panel in my program that acts like a shell. So throughout the lifetime of the program, in addition to interacting with the program the user can also use it as if it were a shell - kind of like a Unix xterm, with additional capabilities. For example, the user could type "ls", then point to a file name, right-click on it and it would open up an editor for that file (based on what kind of file it is), or if it is the name of a directory, cd to that directory and possibly execute ls in that directory. Typing "<Ctrl>+U" would execute "cd ..;pwd;ls", plus other features.
>
> I have written something like this in C using Motif, and it works fine - I just fork at the beginning and the child becomes a shell, and I redirect the pipes such that I have access to the shell's input, output, and error streams.
>
> But I don't know how to do this in Java.

     Quick and (very) dirty, Windows version:


import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.Reader;
import java.io.Writer;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;

public class Foo extends JPanel {

    private final JTextArea screen;
    private final Process shellProcess;
    private final Writer shellInput;
    private final Reader shellOutput;

    private Foo() throws IOException {
       assert SwingUtilities.isEventDispatchThread();
       screen = new JTextArea(24, 80);
       add(new JScrollPane(screen));

       ProcessBuilder builder = new ProcessBuilder();
       builder.command("cmd");
       builder.redirectErrorStream(true);
       shellProcess = builder.start();
       shellInput = new OutputStreamWriter(shellProcess.getOutputStream());
       shellOutput = new InputStreamReader(shellProcess.getInputStream());

       Runnable listener = () -> {
          char[] buffer = new char[512];
          int len;
          do {
             String text;
             try {
                len = shellOutput.read(buffer);
                text = (len >= 0) ? new String(buffer, 0, len) : "*** 
EOF ***";
             } catch (IOException ex) {
                len = -1;
                text = "*** " + ex.getLocalizedMessage() + " ***";
             }

             final String finalText = text;
             SwingUtilities.invokeLater(() -> {
                screen.append(finalText);
             });
          } while (len >= 0);
       };
       new Thread(listener).start();
    }

    public void stopProcess() {
       shellProcess.destroyForcibly();
    }

    private static final String NEWLINE = 
System.getProperty("line.separator");

    public void sendCommand(String command) {
       if (!command.endsWith(NEWLINE)) {
          command += NEWLINE;
       }
       try {
          shellInput.write(command);
          shellInput.flush();
       } catch (IOException ex) {
          Logger.getLogger(Foo.class.getName()).log(Level.SEVERE, null, ex);
          System.exit(1);
       }
    }

    public static void main(String[] unused) {
       SwingUtilities.invokeLater(() -> {
          JFrame frame = new JFrame("Foo");

          final Foo foo;
          try {
             foo = new Foo();
          } catch (IOException ex) {
             Logger.getLogger(Foo.class.getName()).log(Level.SEVERE, 
null, ex);
             System.exit(1);
             return;  // to placate the compiler
          }
          frame.add(foo, BorderLayout.CENTER);

          final JTextField command = new JTextField(60);
          command.addActionListener((ActionEvent e) -> {
             foo.sendCommand(command.getText());
          });
          JLabel label = new JLabel("Command me:");
          label.setLabelFor(command);
          JPanel controls = new JPanel();
          controls.add(label);
          controls.add(command);
          frame.add(controls, BorderLayout.SOUTH);

          frame.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
          frame.addWindowListener(new WindowAdapter() {
             @Override
             public void windowClosing(WindowEvent e) {
                foo.stopProcess();
                System.exit(0);
             }
          });

          frame.pack();
          frame.setVisible(true);
       });
    }
}

-- 
esosman@comcast-dot-net.invalid
"Don't be afraid of work. Make work afraid of you." -- TLM