Executing program from Java program?

Newbie & Debugging Questions
#1

What I have works fine in Windows but doesn’t work on OS X. The strange thing about it is that if it’s run from the command line in OS X, it works, but using Java, it doesn’t work for some reason. To be specific, “nothing” happens. No errors, exceptions, freezing or windows. The program just proceeds as if nothing happened.

Here’s the code (slightly modified to make it clearer).


		Runtime r = Runtime.getRuntime();
		
		try
		{
			String command = "java -Djava.library.path=blah -jar blah.jar";
			r.exec(command);
		}
		
		catch(Exception ex)
		{
			System.out.println("Caught exception " + ex.getMessage());
		}
#2

First of all, what you’re doing will probably crash the sub-process anyway, because you’re not taking the Process instance and read the out/err streams from it, so eventually the buffers will get full, and block the sub-process execution.

So, take the streams, and while you’re at it, print them to your console, as they are very likely to tell you exactly what is happening and why it’s not working like you expected.

#3

Hmm. Still no luck on this issue (only on Linux and OS X). The streams complain about not allowing spaces in paths despite my enclosing these paths in quotes.

#4

that’s some code I use to run Java Webstart from Windows, Linux and Mac OS X. Sorry it’s long - but you should somehow find your solutions inside ;D (NOTE: replace “javaws” with “java”)

package king.lib.access;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.URLConnection;

import javax.swing.JOptionPane;

/**
 * Allows to run a webstart application.
 *
 * @author  Christoph Aschwanden
 * @since  March 30, 2006
 */
public final class WebstartRunner {

  
  /**
   * Private to prevent instantiation of this class.
   */
  private WebstartRunner() {
    // does nothing.
  }
  
  /**
   * Runs the inputted jnlp file. 
   * 
   * @param jnlp  The location of the online jnlp to run.
   * @param localVersion  The version of the installer we are running to start the jnlp.
   */
  public static void run(String jnlp, int localVersion) {
    // find if OS is windows
    String osName = System.getProperty("os.name").toLowerCase();
    boolean windowsOS = osName.indexOf("windows") >= 0;
    boolean macOSX = osName.indexOf("mac os x") >= 0;

    // find Java home directory
    String javaHome = System.getProperty("java.home");
    String fileSeparator = System.getProperty("file.separator");
    
    // set quoting style (windows only can use quotes)
    String quote = windowsOS ? "\"" : "";
    
    // check if version is still good
    String jnlpPath = jnlp.substring(0, jnlp.lastIndexOf("/") + 1);
    String requiredVersionFile = jnlpPath + "RequiredWebstartRunner.version";
    try {
      // find remote version
      URL url = new URL(requiredVersionFile);
      URLConnection connection = url.openConnection();
      BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
      String line = reader.readLine();
      int remoteVersion = Integer.parseInt(line);
      
      // check if still valid
      if (remoteVersion > localVersion) {
        // tell newer version available
        JOptionPane.showMessageDialog(null
            , "A new version of the Aevum Obscurum game client is available!\n"
            + "Please go to http://www.aevumobscurum.com for information and download.\n"
            + "\n"
            + "Your Installed Version: V" + localVersion + "\n"
            + "Required Version: V" + remoteVersion + "\n"
            + "\n"
            , "Aevum Obscurum: New Version Available."
            , JOptionPane.ERROR_MESSAGE);

        // need to redownload!
        System.out.println("Redownload of installer required. New version available");
      }
      else {
        // build list of commands
        String[] cmd = new String[2];
        if (macOSX) {
          cmd[0] = "javaws"; 
        }
        else {
          cmd[0] = quote + javaHome + fileSeparator + "bin" + fileSeparator + "javaws" + quote;
        }
        cmd[1] = jnlp;
        
        // set property!
        System.setProperty("runtime.start.method", "install4j");
        System.setProperty("runtime.start.version", "" + localVersion);
        
        // and execute command!
        try {
          Runtime.getRuntime().exec(cmd);
        }
        catch (IOException e) {
          System.err.println("Cannot start the webstart file (" + jnlp + "): " + e);
        }
      }
    }
    catch (IOException e) {
      // server down or file not found - connection cannot be established
      JOptionPane.showMessageDialog(null
          , "The connection to the Aevum Obscurum server could not be established.\n"
          + "Please try again later or go to http://www.aevumobscurum.com for further "
          + "information.\n"
          + "\n"
          + "We apologize for any inconvenience this might cause you.\n"
          + "\n"
          + "\n"
          , "Error Connecting to Aevum Obscurum Server"
          , JOptionPane.ERROR_MESSAGE);
      
      // output error to console
      System.err.println("IO exception (" + requiredVersionFile + "): " + e);
    }
  }
  
  /** 
   * The main method which will be called.
   *
   * @param args  The arguments for the webstart runner. 
   *              args[0] should be the location of the .jnlp file to run. 
   *              args[1] the version of the installer.
   */
  public static void main(String[] args) {
    run(args[0], Integer.parseInt(args[1]));
  }
}
#5

It turned out to be a variety of issues, but they all linked back to the fact that Linux and OS X don’t like quotes in the command line, despite me using them fine in the shell scripts I provided for Linux users.