Running Command Line in Java [duplicate]

Question

Is there a way to run this command line within a Java application?

java -jar map.jar time.rel test.txt debug

I can run it with command but I couldn't do it within Java.

Tripod

I have tried, Runtime rt = Runtime.getRuntime();Process proc = rt.exec("ping localhost"); – Tripod

Do you want to launch a VM from within another VM? – Beady

You can try my small library Jaxec – Ruwenzori

Answer 1

Runtime rt = Runtime.getRuntime();
Process pr = rt.exec("java -jar map.jar time.rel test.txt debug");

http://docs.oracle.com/javase/7/docs/api/java/lang/Runtime.html

Janessa

is it normal that when i try to output it to console it only outputs something like this: java.lang.ProcessImpl@6ecec5288 – Tripod

Use pr.getInputStream(). Here is a detailed example: linglom.com/2007/06/06/… – Janessa

It's useful to check what the process returns with. You can get that with pr.waitFor(). So it looks like this: int retVal = pr.waitFor(). So if it's not 0, you can abort / clean up. – Oehsen

Is there a practical/meaningful difference between pr.exitValue and pr.waitFor()? Update: I think exitValue will throw an exception if the process has not finished where as waitFor... you know – Twoply

nothing it's more java than "Runtime rt = Runtime.getRuntime();" – Veilleux

This answer is problematic. The called app will block unless you read BOTH stderr and stdout. You will get away with it if only a small amount of output is written but once the buffer is exceeded everything stops. – Esbjerg

Answer 2

You can also watch the output like this:

final Process p = Runtime.getRuntime().exec("java -jar map.jar time.rel test.txt debug");

new Thread(new Runnable() {
    public void run() {
        BufferedReader input = new BufferedReader(new InputStreamReader(p.getInputStream()));
        String line = null;

        try {
            while ((line = input.readLine()) != null)
                System.out.println(line);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}).start();

p.waitFor();

And don't forget, if you are running a windows command, you need to put cmd /c in front of your command.

EDIT: And for bonus points, you can also use ProcessBuilder to pass input to a program:

String[] command = new String[] {
        "choice",
        "/C",
        "YN",
        "/M",
        "\"Press Y if you're cool\""
};
String inputLine = "Y";

ProcessBuilder pb = new ProcessBuilder(command);
pb.redirectErrorStream(true);
Process p = pb.start();
BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()));
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(p.getOutputStream()));

writer.write(inputLine);
writer.newLine();
writer.close();

String line;

while ((line = reader.readLine()) != null) {
    System.out.println(line);
}

This will run the windows command choice /C YN /M "Press Y if you're cool" and respond with a Y. So, the output will be:

Press Y if you're cool [Y,N]?Y

Lorettalorette

You can also use p.getErrorStream to understand why your command is broken! – Interstadial

@Craigo: any reference regarding your "cmd /c" statement? thx – Pastelist

Actually, I think you only need the "cmd /c", if you are wanting to run a windows command, like "copy". Apologies for the confusion. – Lorettalorette

this doesn't print the whole output for me. executing "ls" prints different amounts of the directory contents each time. this works best for me: alvinalexander.com/java/edu/pj/pj010016 – Catwalk

Answer 3

To avoid the called process to be blocked if it outputs a lot of data on the standard output and/or error, you have to use the solution provided by Craigo. Note also that ProcessBuilder is better than Runtime.getRuntime().exec(). This is for a couple of reasons: it tokenizes better the arguments, and it also takes care of the error standard output (check also here).

ProcessBuilder builder = new ProcessBuilder("cmd", "arg1", ...);
builder.redirectErrorStream(true);
final Process process = builder.start();

// Watch the process
watch(process);

I use a new function "watch" to gather this data in a new thread. This thread will finish in the calling process when the called process ends.

private static void watch(final Process process) {
    new Thread() {
        public void run() {
            BufferedReader input = new BufferedReader(new InputStreamReader(process.getInputStream()));
            String line = null; 
            try {
                while ((line = input.readLine()) != null) {
                    System.out.println(line);
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }.start();
}

Inadvertent

Thank you for pointing that out, I was actually struggling because I had no stderr. – Redheaded

Answer 4

Runtime.getRuntime().exec("java -jar map.jar time.rel test.txt debug");

Toxoplasmosis

The shortest code is always my favorite. – Hectoliter

Answer 5

import java.io.*;

Process p = Runtime.getRuntime().exec("java -jar map.jar time.rel test.txt debug");

Consider the following if you run into any further problems, but I'm guessing that the above will work for you:

Problems with Runtime.exec()

Oxalate

Answer 6

what about

public class CmdExec {

public static Scanner s = null;


public static void main(String[] args) throws InterruptedException, IOException {
    s = new Scanner(System.in);
    System.out.print("$ ");
    String cmd = s.nextLine();
    final Process p = Runtime.getRuntime().exec(cmd);

    new Thread(new Runnable() {
        public void run() {
            BufferedReader input = new BufferedReader(new InputStreamReader(p.getInputStream()));
            String line = null; 

            try {
                while ((line = input.readLine()) != null) {
                    System.out.println(line);
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }).start();

    p.waitFor();
     }

 }

Cheeseburger

Answer 7

Process p = Runtime.getRuntime().exec("java -jar map.jar time.rel test.txt debug");

Hoahoactzin

Answer 8

Have you tried the exec command within the Runtime class?

Runtime.getRuntime().exec("java -jar map.jar time.rel test.txt debug")

Runtime - Java Documentation

Blastula