CODEWITHSUNDEEP
javaprocessinputstream
Prior99
Prior99

Reputation: 619

Read the output of a process fluidly in Java

In java, I am trying to read the output from a consoleprogram I wrote in C. This program is continuously printing its current progress into stdout using printf(). If I run that program in a console, everything is fine, I am seeing the output. I am now trying to run it from inside java, which also runs fine, the process is starting and calculating, but the whole output however will be read in huge blocks at once (There is no output for some seconds and then everything appears at once).

I assume there is some kind of a buffer in between that must be filled.

In order to draw a progressbar and work with other parameters the program is printing it is neccessary to read from the stdout fluidly and not everything at once.

I already read about this in Questions like Problem reading InputStream from Java Process (Runtime.getRuntime().exec() or ProcessBuilder), but this did not help me very much as I followed the tips in these questions.

Below is the code I am currently trying to use.

public static void main(String[] args)
{
    ProcessBuilder builder = new ProcessBuilder("render.exe", "1920", "1080", "10000", "0", "0", "1", "6", "test.png");
    try
    {
        final Process proc = builder.start();
        final Thread io = new Thread()
        {
            @Override
            public void run()
            {
                final InputStream read = proc.getInputStream();
                int c;
                try
                {
                    while((c = read.read()) != -1)
                        System.out.print((char)c);
                }
                catch (IOException e)
                {
                    e.printStackTrace();
                }
            }
        };
        io.start();
        proc.waitFor();
    }
    catch (IOException | InterruptedException e)
    {
        e.printStackTrace();
    }

}

Upvotes: 1

Views: 303

Answers (1)

Joni
Joni

Reputation: 111369

The C program probably detects that its stdout is not connected to an interactive console and buffers its output; you cannot change this from Java.

Assuming you use stdio, to make the C program produce output more fluidly you can add fflush(stdout) in appropriate places, or you can disable buffering with a call to setvbuf:

setvbuf(stdout, NULL, _IONBF, 0);

Upvotes: 1

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