Program Locking in While

Question

I’m working on a project and I’m having problems with the same, this program I’m posting is similar to what I’m working on.

The problem is this: it arrives in while, the program does its function, then hangs and does not come out.

I’ve tried everything. Could someone give some suggestion?

public class CommandZ {

private static String Command;
private static Scanner scan;


public static void main(String[] args) {        
    scan = new Scanner(System.in);


        System.out.println("Shell: ");
        Command = scan.nextLine();

        ProcessBuilder pb = new ProcessBuilder("powershell.exe", "-Command", Command);
        Process p;
        try {
            p = pb.start();
        } catch (IOException e) {
            System.out.println("Failed to start powershell");
            return;
        }


        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(p.getInputStream()));
        String line;
        System.out.println("Begin!");
        try {
            //PROBLEMA AQUI
            while((line = bufferedReader.readLine()) != null){
                System.out.println(line);
                //Imprimi as linhas, e não da sequência no programa..




            }
        } catch (IOException e) {
            System.out.println("Failed to read line");
            return;
        }

        System.out.println("Exit");


    }

Answer 1

This code can solve your problem.

The source is this chatting, specifically at the end of the conversation.

Code:

import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintStream;
import java.io.PrintWriter;


public class Gobbler implements Runnable {

    private PrintStream out;
    private String message;

    private BufferedReader reader;

    public Gobbler(InputStream inputStream, PrintStream out) {
        this.reader = new BufferedReader(new InputStreamReader(inputStream));
               this.out = out;
        this.message = ( null != message ) ? message : "";
    }

    public void run() {
        String line;

        try {
            while (null != (line = this.reader.readLine())) {
                out.println(message + line);
            }
            this.reader.close();
        } catch (IOException e) {
            System.err.println("ERROR: " + e.getMessage());
        }
    }
}


class PowerConsole {

    private ProcessBuilder pb;
    Process p;
    boolean closed = false;
    PrintWriter writer;

    PowerConsole(String[] commandList) {
        pb = new ProcessBuilder(commandList);
        try {
            p = pb.start();
        } catch (IOException ex) {
            throw new RuntimeException("Cannot execute PowerShell.exe", ex);
        }
        writer = new PrintWriter(new OutputStreamWriter(new BufferedOutputStream(p.getOutputStream())), true);
        Gobbler outGobbler = new Gobbler(p.getInputStream(), System.out);
        Gobbler errGobbler = new Gobbler(p.getErrorStream(), System.out);
        Thread outThread = new Thread(outGobbler);
        Thread errThread = new Thread(errGobbler);
        outThread.start();
        errThread.start();
    }

    public void execute(String command) {
        if (!closed) {
            writer.println(command);
            writer.flush();
        } else {
            throw new IllegalStateException("Power console has ben closed.");
        }
    }

    public void close() {
        try {
            execute("exit");
            p.waitFor();
        } catch (InterruptedException ex) {
        }
    }

    public static void main(String[] args) throws IOException, InterruptedException {
        PowerConsole pc = new PowerConsole(new String[]{"powershell.exe", "-NoExit", "-Command", "-"});
        System.out.println("========== Executing dir");
        pc.execute("dir"); 
//        System.out.println("========== Executing cd\\");
//        pc.execute("cd \\"); Thread.sleep(2000);
//        System.out.println("========== Executing dir");
//        pc.execute("dir"); Thread.sleep(2000);
//        System.out.println("========== Executing cd \\temp");
//        pc.execute("cd \\temp"); Thread.sleep(2000);
//        System.out.println("========== Executing dir");
//        pc.execute("dir"); Thread.sleep(2000);
//        System.out.println("========== Executing cd \\bubba");
//        pc.execute("cd \\bubba"); Thread.sleep(2000);
        System.out.println("========== Exiting .... bye.");
        pc.close();
    }
}

Answer 2

I found a solution in stackoverflow.with:

ProcessBuilder proc = new ProcessBuilder().inheritIO().command(
                "powershell.exe", "-Command", Command);
        proc.redirectErrorStream(true);
        Process p = proc.start();
        BufferedReader bufferedReader = new BufferedReader(
                new InputStreamReader(p.getInputStream()));
        String line;
        while ((line = bufferedReader.readLine()) != null) {
            System.out.println(line);

Answer 3

Guess your problem is because the "powershell.exe" is waiting for command in Runtime. And because of that the while "hangs" on execution. Because Process is waiting for new data to be read.

I found this link who talks about it.

I also ran some tests running on Windows. Calling cmd.exe and passing the commands, the same hangs on while. Because I imagine he’s waiting for new commands to keep returning in the Inputstreamreader. But when I run only one command like ipconfig. It usually finishes the program.

Well I hope I helped ^^

Answer 4

Your mistake has to do with logic. You did not guarantee that the variable line reach the value null therefore the while repeats indefinitely. You should do this at the end of the while, I added before the comment:

...
while((line = bufferedReader.readLine()) != null){
    System.out.println(line);
    line = null;
 //Imprimi as linhas, e não da sequência no programa..
...