How to Properly Execute Multiple Command-Line Commands in Java?

How to Execute Command Line Arguments Via Java

Question:

How do you execute command line arguments through Java? For example, consider the following code:

// Execute command
String command = "cmd /c start cmd.exe";
Process child = Runtime.getRuntime().exec(command);

// Get output stream to write from it
OutputStream out = child.getOutputStream();

out.write("cd C:/ /r/n".getBytes());
out.flush();
out.write("dir /r/n".getBytes());
out.close();

This code opens the command line but doesn't execute the "cd" or "dir" commands.

Answer:

To reuse a single process for multiple commands in Windows, follow these steps:

1. Create a String array with the command name, in this case, "cmd".
2. Execute the command using Runtime.getRuntime().exec(command).
3. Start threads to handle error and output streams.
4. Open a PrintWriter on the output stream.
5. Write the desired commands to the PrintWriter.
6. Close the PrintWriter.
7. Wait for the process to complete with p.waitFor().

Here's an example:

String[] command = {"cmd"};
Process p = Runtime.getRuntime().exec(command);
new Thread(new SyncPipe(p.getErrorStream(), System.err)).start();
new Thread(new SyncPipe(p.getInputStream(), System.out)).start();
PrintWriter stdin = new PrintWriter(p.getOutputStream());
stdin.println("dir c:\ /A /Q");
stdin.close();
int returnCode = p.waitFor();
System.out.println("Return code = " + returnCode);

SyncPipe Class:

class SyncPipe implements Runnable {
    public SyncPipe(InputStream istrm, OutputStream ostrm) {
        istrm_ = istrm;
        ostrm_ = ostrm;
    }

    public void run() {
        try {
            final byte[] buffer = new byte[1024];
            for (int length = 0; (length = istrm_.read(buffer)) != -1; ) {
                ostrm_.write(buffer, 0, length);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private final OutputStream ostrm_;
    private final InputStream istrm_;
}

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