How Can I Efficiently Execute Multiple Command Line Commands from a Java Program?

Executing Command Line Commands via Java

Executing external commands from a Java program can be useful for automating tasks or accessing system functionality. However, as demonstrated in the initial question, simply using Runtime.getRuntime().exec() may not yield the desired behavior, especially when interacting with the Windows command prompt.

To resolve this issue, a more advanced approach is required. As suggested in the quoted post, one effective solution involves reusing a process to execute multiple commands. The following code exemplifies this technique:

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");
// Add additional commands here
stdin.close();
int returnCode = p.waitFor();
System.out.println("Return code = " + returnCode);

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

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

    private final OutputStream ostrm_;
    private final InputStream istrm_;
}

Explanation:

• The code launches a cmd process, keeping it alive for subsequent commands.
• Two threads are created to handle the process's input and output streams, ensuring real-time interaction.
• stdin is used to send the command "dir c: /A /Q" to the command prompt.
• The process executes this command and any additional commands sent through stdin.
• p.waitFor() blocks until the command finishes, ensuring the completion of all tasks before proceeding.
• The return code is checked to indicate the success or failure of the executed commands.

This approach allows for a more interactive execution of commands on the Windows command prompt from within a Java application.

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