Execute an external program

import java.io.*;
public class CmdExec {

  public static void main(String argv[]) {
    try {
      String line;
      Process p = Runtime.getRuntime().exec
        (System.getenv("windir") +"\\system32\\"+"tree.com /A");
      BufferedReader input =
        new BufferedReader
          (new InputStreamReader(p.getInputStream()));
      while ((line = input.readLine()) != null) {
        System.out.println(line);
      }
      input.close();
    }
    catch (Exception err) {
      err.printStackTrace();
    }
  }
}

Windows CMD (or BAT) file and retrieve the errorlevel or exitcode

// win xp
import java.io.*;
public class CmdExec {
  public static void main(String argv[]) {
    try {
      String line;
      Process p = Runtime.getRuntime().exec("test.cmd");
      p.waitFor();
      System.out.println(p.exitValue());
    }
    catch (Exception err) {
      err.printStackTrace();
    }
  }
}

@echo hello world
@exit 42

Launch a Unix script

String[] cmd = {"/bin/sh", "-c", "ls > hello"};
Runtime.getRuntime().exec(cmd);

Using the ProcessBuilder

   
import java.io.*;
import java.util.*;

public class CmdProcessBuilder {
  public static void main(String args[]) 
     throws InterruptedException,IOException 
  {
    List<String> command = new ArrayList<String>();
    command.add(System.getenv("windir") +"\\system32\\"+"tree.com");
    command.add("/A");

    ProcessBuilder builder = new ProcessBuilder(command);
    Map<String, String> environ = builder.environment();
    builder.directory(new File(System.getenv("temp")));

    System.out.println("Directory : " + System.getenv("temp") );
    final Process process = builder.start();
    InputStream is = process.getInputStream();
    InputStreamReader isr = new InputStreamReader(is);
    BufferedReader br = new BufferedReader(isr);
    String line;
    while ((line = br.readLine()) != null) {
      System.out.println(line);
    }
    System.out.println("Program terminated!");
  }
}

Windows rundll32 utility

// "file" is the filename of the data file 
//  ex. myresume.doc 
//  to start Word if the doc extension is associated with it.
Runtime.getRuntime().exec
  ("rundll32 SHELL32.DLL,ShellExec_RunDLL " + file.getAbsolutePath());

See also this HowTo about the new Desktop API, the recommended solution (but you need JDK1.6).
See also this one to open the default browser.

[Dialup.java]
public class Dialup {
  public static void main(String[] args) throws Exception {
    Process p = Runtime.getRuntime()
      .exec("rundll32.exe rnaui.dll,RnaDial MyConnection");
    p.waitFor();
    System.out.println("Done.");
  }
}

You still need to press ENTER to CONNECT, there is an option in the Connection properties to connect automatically.

rasdial "connection name"
rasdial "connection name" /d to drop
rasdial /? for more options

PDF (Windows only)

public class ShowPDF {
  public static void main(String[] args) throws Exception {
    Process p = 
      Runtime.getRuntime()
        .exec("rundll32 url.dll,FileProtocolHandler c:/pdf/mypdf.pdf");
    p.waitFor();
    System.out.println("Done.");
  }
}

PDF (Mac only)

public class ShowPDF {
  public static void main (String[] args) throws Exception{
    Process p = Runtime.getRuntime().exec("open /Documents/mypdf.pdf");
  }
}

Path to executable with spaces in them

You can include a path for the program to be executed. On the Win plateform, you need to put the path in quotes if the path contains spaces.

 
public class Test {
  public static void main(String[] args) throws Exception {
    Process p = Runtime.getRuntime().exec(
       "\"c:/program files/windows/notepad.exe\"");
    p.waitFor();
  }
}

If you need to pass arguments, it's safer to a String array especially if they contain spaces.

String[] cmd = { "myProgram.exe", "-o=This is an option" };
Runtime.getRuntime().exec(cmd);

String fileName = "c:\\Applications\\My Documents\\test.doc";
String[] commands = {"cmd", "/c", "start", "\"DummyTitle\"",fileName};
Runtime.getRuntime().exec(commands);

VBSCRIPT

// Win9x
Runtime.getRuntime().exec("start myscript.vbs");

// WinNT
Runtime.getRuntime().exec("cmd /c start myscript.vbs");

or

// with a visible console
Runtime.getRuntime().exec("cscript myscript.vbs");

// with no visible console
Runtime.getRuntime().exec("wscript myscript.vbs");

HTML Help (Windows only)

Runtime.getRuntime().exec("hh.exe myhelpfile.chm");

Start Excel

import java.io.IOException;

class StartExcel {
    public static void main(String args[])
        throws IOException
    {
        Runtime.getRuntime().exec("cmd /c start excel.exe");
    }
}

import java.io.IOException;

class StartExcel {
    public static void main(String args[])
        throws IOException
    {
        String fileName = "c:\\temp\\xls\\test2.xls";
        String[] commands = {"cmd", "/c", "start", "\"DummyTitle\"",fileName};
        Runtime.getRuntime().exec(commands);
    }
}