Java - passing input into external C/C++ application

Question

I'm trying to enter some value in external application using Java.

Java application looks like this:

Runtime runtime = Runtime.getRuntime();
// ... str build ...
proc = runtime.exec(str);
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(proc.getOutputStream()));
bw.write(value);
bw.flush();
bw.close();
if (proc.waitFor() != 0) 
    // error msg
// the end

Application hangs at waitFor method.

External application looks like this:

welcome banner

please enter 8 character input:

Welcome banner is printed using printf and input is taken with SetConsoleMode/ReadConsoleInput. ReadConsoleInput reads one char and they are masked with * character.

Help

Answer 1

you can use:

proc.getOutputStream().write("some date".getBytes())

keep in mind that you HAVE to read everything the app send to stdout and stderr, else it might get stuck writing there. I use a generic class to read it in a different thread. usage is like:

InputStreamSucker inSucker = new InputStreamSucker(proc.getInputStream());
InputStreamSucker errSucker = new InputStreamSucker(proc.getErrorStream());
proc.waitFor();
int exit = process.exitValue();
inSucker.join();
errSucker.join();

InputStreamSucker code is here:

public class InputStreamSucker extends Thread
{
    static Logger logger = Logger.getLogger(InputStreamSucker.class);

    private final BufferedInputStream m_in;

    private final ByteArrayOutputStream m_out;

    private final File m_outFile;

    public InputStreamSucker(InputStream in) throws FileNotFoundException
    {
     this(in, null);
    }


    public InputStreamSucker(InputStream in, File outFile) throws FileNotFoundException
    {
     m_in = new BufferedInputStream(in, 4096);
     m_outFile = outFile;
     m_out = new ByteArrayOutputStream();
     start();
    }

    @Override
    public void run()
    {
     try
     {
      int c;
      while ((c = m_in.read()) != -1)
      {
       m_out.write(c);
      }
     }
     catch (IOException e)
     {
      logger.error("Error pumping stream", e);
     }
     finally
     {
      if (m_in != null)
      {
       try
       {
        m_in.close();
       } 
       catch (IOException e)
       {
       }
      }

      try
      {
       m_out.close();
      }
      catch (IOException e)
      {
       logger.error("Error closing out stream", e);
      }

      if (m_outFile != null)
      {
       byte data[] = m_out.toByteArray();
       if (data.length > 0)
       {
        FileOutputStream fo = null;
        try
        {
         fo = new FileOutputStream(m_outFile);
         fo.write(data);
        }
        catch (IOException e)
        {
         logger.error("Error writing " + m_outFile);
        }
        finally
        {
         try
         {
          if (fo != null) fo.close();
         }
         catch (IOException e)
         {
          logger.error("Error closing " + m_outFile);
         }
        }
       }
      }
     }
    }

    public String getOutput()
    {
     return new String(m_out.toByteArray());
    }
}

Answer 2

Still not working :-(

I'm trying to recreate external application using disassembly code and this is pretty close to it ... Imagine this as a external C/C++ application in which I'm trying to enter value using Java:

HANDLE hStdin = GetStdHandle(STD_INPUT_HANDLE); 
DWORD cNumRead;
INPUT_RECORD irBuffer[1]; 
int x = 0;

printf("\nwelcome banner\n\nplease enter 8 characters: ");

SetConsoleMode(hStdin, 0);
do {
 ReadConsoleInput(hStdin, irBuffer, 1, &cNumRead);
 for (int i = 0; i < 8; i++) {
  switch (irBuffer[i].EventType) {
   case KEY_EVENT:
    if (irBuffer[i].Event.KeyEvent.bKeyDown) {
     printf("*");
     fflush(stdout);
     x++;
    }
    break;
   default:
    break;
  }
 }
} while (x < 8);

printf("\nsuccessfully finished\n");

return 0;

Answer 3

Got the answer! The trick is to use WriteConsoleInput() API because program expects keyboard event, not text ... That's why the waitFor() waited forever! :)

Answer 4

Hey johnhy, I think that I'm having the same problem as you, could you please explain a little further what you mean about using WriteConsoleInput() API? I've looked for documentation about it but I don't see any API for Java.

Here's the question I've posted regarding my problem.

http://stackoverflow.com/questions/3240704/execute-external-program-using-processbuilder-and-provide-input

Thanks a lot, and sorry for asking more questions instead of giving an answer. Regards.