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November 2001



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Regarding the Runtime.getRuntime().exec(String cmd)

Posted by Hiran on November 14, 2001 at 3:18 AM

What I'm wondering is how to use Runtime.getRuntime().exec(String cmd) to open up a file? I want to open up an mp3 file using the configured player (on my computer, it's Winamp) and play it. The following bit of code (created by Matt) works with 'start "c:\a - d.mp3"' (w/o the single quotes) a string argument passed to Runtime.getRuntime().exec(String cmd). (I've changed the original code to display the exact cmd string passed to Runtime's exec method. Just enter in the text field 'start "c:\a - d.mp3"' (w/o the single quotes), where c:\a - d.mp3 is an actual mp3 file):

* Copyright 2001, by Matt Gerrans.
// I suppose "import javax.swing.*" would be more succinct, but
// just in case your productivity is being meaasured by LOC:
import javax.swing.JTextField;
import javax.swing.JTextArea;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JButton;
import javax.swing.JScrollPane;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.Container;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

public class ExecTester {
* A simple tester for Runtime.exec(). Could easily be adapted to
* testing other API calls (Hmm... maybe it shouldn't be called
* "ExecTester" in that case...). ExecTester runs as a console app
* (no GUI) or as a Swing application. You give no command line
* parameters, or the command line option /showui, the GUI will
* appear. Otherwise, it is assumed that the first parameter on
* command line is to be passed to Runtime.exec().
* Note (on Windows platform, for sure and I think also on unix
* platforms), if you want to include spaces (i.e. multipart
* command, as in a program to execute with parameters) you
* must put quotes around the whole thing, like so:
* java ExecTester "notepad c:\autoexec.bat"
* In case you didn't know it, that causes the whole thing to be
* packaged in args[0] (or argv[0] in C/C++).
JTextField commandField;
JTextArea outputText;
* Shows a simple Swing UI for testing exec(). This is handy when
* you want to try several different exec()s.
public void showUI()
JFrame frame = new JFrame("Runtime.exec() Tester");
// frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
// Sun docs say use JFrame.EXIT_ON_CLOSE, but it doesn't exist,
// (in JDK 1.2, at least) so I'll add this window adapter:
frame.addWindowListener( new WindowAdapter()
public void windowClosing(WindowEvent e)
Container pane = frame.getContentPane();
pane.setLayout( new java.awt.FlowLayout() );
pane.add(new JLabel("Enter your command:"));

commandField = new JTextField("notepad c:\\windows\\win.ini", 30);

final JButton goButton = new JButton("Execute It!");

goButton.addActionListener( new goButtonListener() );
pane.add( new JLabel( "Results of execution:" ) );
outputText = new JTextArea(5,50);
pane.add( new JScrollPane(outputText) );

frame.setSize( 600, 200 );
// Yes, I'm ashamed of hard-coding the window size, but the default
// JFrame wasn't coming up nicely arranged. This could probably
// be fixed by fooling with more frames and layouts, but I'll leave
// that as an exercise for whomever wishes to pursue it.
* Runs the exec() and adds its output to the results area.
class goButtonListener implements ActionListener
public void actionPerformed(ActionEvent e)
outputText.append( runExec( commandField.getText() ) );
* Executes Runtime.exec() and returns the results is a
* human-readable string.
* @param cmd The command to send to Runtime.exec().
public static String runExec( String cmd )
String results = "Results of Runtime.getRuntime().exec( \"" +
cmd + "\" ):";
Runtime.getRuntime().exec( cmd );
results += " No problem.";
catch( e )
results += "\n " + e.toString();
return results + "\n";
* Displays the UI or simply runs the command line, depending upon
* what's specified by args[0].
* @param args The usual thing.
public static void main( String[] args )
if( args.length == 0 || args[0].equals( "/showui" ) )
(new ExecTester()).showUI();
System.out.println( "Runtime.getRuntime().exec( \"" +
args[0] + "\" ): " + runExec(args[0]));

But when I pass 'start "c:\a - d.mp3"' (w/o the single quotes) as a parameter to Runtime's exec method in the following code:

public class TestClass {
public TestClass() {

public void main(String[] args) throws {
String cmd = "start \"c:\\a - d.mp3\"";

it compiles, but does nothing. Anyone know why?


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