executing java commands using a java program

[nagsen kamble]

Hi,

Instead from command prompt, I am trying to execute java commands like 'javac', 'java' using java program. I have tried Runtime.getRuntime().exec() but it only executes the DOS commands like 'del'. samples those i tried are:

with taking commands as String[],

1.
commands[0] = "cmd";
commands[1] = "javac C:\\test.java";

2.
commands[0] = "cmd";
commands[1] = "javac";
commands[2] = "C:\\test.java";

3.
commands[0] = "cmd";
commands[1] = "set";
commands[2] = "path=C:\\Program Files\\IBM\\WebSphere Studio\\Application Developer IE\\v5.1\\runtimes\\base_v5\\java\\bin";
commands[3] = "javac C:\\test.java";

But none of above is working...no error/exception occurs but nothing happen. Just command prompt comes and disappears but no other action is happening....only DOS command such as following 'del' is working:

commands[0] = "cmd";
commands[1] = "del";
commands[2] = "C:\\test.java";

The lines used to execute are:

Runtime r= Runtime.getRuntime();
Process p=null;
try
{
p=r.exec(commands);
}catch(Exception e)
{
System.out.println("Exception is:- "+e.getMessage());
}

Could you please tell me what is the way to execute java commands using java programming language?

My ultimate intention is to execute java commands (jar - xvf and other commands) to jar and unjar the files using java program instead command prompt.

[Rok Štelcer]

Here you go:

import java.io.*;

public class Test
{
	public static void main(String[] args) throws IOException, InterruptedException
	{
		javac("Test.java");
		jar(JAR.CREATE,  "test.jar", "file_1.txt", "file_2.txt", "file_3.txt", "file_4.txt");
		jar(JAR.EXTRACT, "test.jar");
	}

	private static void javac(String src) throws IOException, InterruptedException
	{
		Runtime runtime = Runtime.getRuntime();

		Process process = runtime.exec("cmd");

		OutputStream stdout = process.getOutputStream();

		String line = "javac " + src + " \n";   
		System.out.println(line);

		stdout.write(line.getBytes() );

		stdout.flush();
		stdout.close();

		process.waitFor();
	}

	private static void jar(JAR action, String fileName, String ... files)  throws IOException, InterruptedException
	{
		Runtime runtime = Runtime.getRuntime();

		Process process = runtime.exec("cmd");

		OutputStream stdout = process.getOutputStream();

		String line = null;
		switch (action)
		{
		case CREATE:
			{

				String args = "";
				for (String file : files)
				{
					args += (file + " ");
				}
				line = "jar cf " + fileName + " " + args + " \n"; 
				break;
			}
		case EXTRACT:
			{
				line = "jar xf " + fileName + " \n"; 
				break;
			}
		} 
		System.out.println(line); 

		stdout.write(line.getBytes() );

		stdout.flush();
		stdout.close();

		process.waitFor();
	}

	enum JAR
	{
		CREATE, EXTRACT
	}
}

Regards,
Rok

[Rob Spoor]

Read the Javaworld article "When Runtime().exec won't". You really should.

If you don't need the command window, you can simply skip the "cmd" part and execute the javac command directly:

String[] command = {"javac", src};
Process process = Runtime.exec(command);

About creating the JAR file, I wouldn't do that using command line but using the API itself. Check out the java.util.jar package; you can use a JarOutputStream around a FileOutputStream to write the entries. Writing an entry goes as follows:
1) create a ZipEntry
2) call putNextEntry()
3) write the entire contents of the file to put in the JAR file
4) repeat steps 2 and 3 for all other entries
5) close() the JarOutputStream
You can even add a Manifest.MF file using the Manifest class.

Unpacking the JAR file can be done using JarFile or JarInputStream.

[Campbell Ritchie]

Please search this website; there have been threads about using DOS commands with Runtime.exec() before, but you may have to go back a few years. Some of those commands are specific commands for the command line program, rather than invocations of executables. I can't remember the details, but there will be more in the old thread.

And I presume you have read when Runtime.exec() won't, Michael Daconta's classic article (which I see Rob has quoted too)?