Question

I know there are similar threads, and I have read them all. However none of them have been of any help.

I have this simple batch file:

@echo off
set /p UserInput=Enter a number: 
echo Number was %UserInput%

I want to run this batch file from java, send the number to it and get the input.

I have a strange problem. I started the batch file using cmd /c, opened the input and output streams, but it still won’t work. When I run a program, for example “cmd.exe”, it returns the actual output that you get when you open a CMD window:

Microsoft Windows… Copyright (c) 2009 Microsoft
Corporation. All rights reserved.

So at least the code is partially working. However it simply does not give me ANY output whatsoever when I use "cmd /c C:\\test.bat" (where test.bat is a valid batch file).

This is the java code. What’s wrong with it?

      import java.io.BufferedReader;
    import java.io.BufferedWriter;
    import java.io.IOException;
    import java.io.InputStream;
    import java.io.InputStreamReader;
    import java.io.OutputStream;
    import java.io.OutputStreamWriter;

    public class Test {

        private static BufferedReader bufIn;
        private static BufferedWriter printOut;
        private static Process p;

        public static void main(String[] args) throws IOException {

            Runtime rt = Runtime.getRuntime() ;

            p = rt.exec("cmd.exe /c C:\\test.bat");
            InputStream in = p.getInputStream() ;
            OutputStream out = p.getOutputStream ();

            bufIn = new BufferedReader(new InputStreamReader(in));
            printOut = new BufferedWriter(new OutputStreamWriter(out));

            int ch = 0;
            ch = bufIn.read();

            while (ch != 0) 
            {
                System.out.print((char) ch);
                ch = bufIn.read();
            }

            //send a command to 

            printOut.write("209");
            printOut.flush();

            while (ch != 0) 
            {
                System.out.print((char) ch);
                ch = bufIn.read();
            }



    //p.destroy() ;

    }


}

I should be getting:

Please enter a number:
Number was 209

Edit: I edited the code because it was apparently getting stuck at the readLine while there was no line 🙂

Anyway, I still have a problem.
I’m getting:

Enter a number: 

and nothing else, almost as if the output stream is not working at all.

Answer 1

Instead of using a PrintWriter, try an OutputStreamWriter wrapped in a BufferedWriter:

printOut = new BufferedWriter(new OutputStreamWriter(out));

Obviously you’ll need to change printOut to a BufferedWriter as well.

It also looks like you’re flushing and printing in the wrong order to me, I’d do:

printOut.println("209");
printOut.flush();

As a side point, you can use readLine() on BufferedReader rather than just read()!