Java - Read process output when it's finished

Question

I have a problem in my code

ProcessBuilder pb = new ProcessBuilder("my program.exe","-g");
Process core = pb.start();
if(!core.waitFor(5, TimeUnit.HOURS))
{
    isDestroyed = true;
    core.destroy();
}
else
    isDestroyed = false;

String xmlOutput = IOUtils.toString(core.getInputStream());

And the problem is that it works all the time exactly 5 hours, but when I run it from console, it works <10 seconds. What's the problem? OS is Windows 8.1 64bit.

I want it runs the same time as from console. Or there is another good way to get output? If yes, please say how. Thanks

Do you have a requirement of waiting for 5 hours or you just need to wait till the Process completes? — m3nation
– m3nation, Commented Jun 9, 2015 at 7:18

Hummeling Engineering BV · Accepted Answer · 2015-06-09 08:02:30Z

1

You can have your process return its output while it's processing:

ProcessBuilder pb = new ProcessBuilder("my program.exe","-g");
Process core = pb.start();
InputStream stream = core.getInputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(stream));
String line;
StringBuilder stringBuilder = new StringBuilder();
long end = System.currentTimeMillis() + TimeUnit.HOURS.toMillis(5);

while (System.currentTimeMillis() < end && (line = reader.readLine()) != null) {
    stringBuilder.append(line);
}
stream.close();
String xmlOutput = stringBuilder.toString();

edited Jun 9, 2015 at 8:02

answered Jun 9, 2015 at 7:35

Hummeling Engineering BV

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5 Comments

ivan Over a year ago

It should be limited 5 hours. If I add the lines: long end = System.currentTimeMillis() + TimeUnit.HOURS.toMillis(5); and the condition into the cycle while (System.currentTimeMillis() < end && (line = reader.readLine()) != null) will that work correctly?

Hummeling Engineering BV Over a year ago

@ivan Indeed, that would stop the process after five hours, unless finished earlier.

JohnK Over a year ago

I'm trying to use this algorithm with stderr (viz., InputStream stream = core.getErrorStream()), but there's nothing coming from the readLine. Is that to be expected when there's no error or what am I doing wrong?

Hummeling Engineering BV Over a year ago

@JohnK The readLine() method returns null when there's no errors. Does it do that?

JohnK Over a year ago

@HummelingEngineeringBV Thanks for your reply! I wasn't getting anything but null. But I figured out my problem: I had set .redirectError(ProcessBuilder.Redirect.INHERIT) on the ProcessBuilder and forgetten about it. Thanks again for your reply!

user207421 · Accepted Answer · 2015-06-09 07:29:35Z

0

You're deadlocked for 5 hours waiting for the process to exit while it is waiting for you to consume some input so it won't be blocked producing it so it can exit.

You should consume the input first, and then do the waitFor().

NB You also need to close the output stream to the process so it isn't waiting for input.

answered Jun 9, 2015 at 7:29

user207421

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1 Comment

ivan Over a year ago

My program is a scanner that can work very huge time. But I want to limit this 5 hours. Will that work? I mean that reading can take more than 5 hours, I worry about it

user4910279 · Accepted Answer · 2015-06-09 08:10:37Z

Consume the process's STDOUT in another thread. And main thread waits for the process terminattion.

    ProcessBuilder pb = new ProcessBuilder("my program.exe","-g");
    Process core = pb.start();
    InputStream stream = core.getInputStream();
    BufferedReader reader = new BufferedReader(new InputStreamReader(stream));
    StringBuilder stringBuilder = new StringBuilder();
    new Thread(() -> {
        try {
            String line;
            while ((line = reader.readLine()) != null) {
                stringBuilder.append(line);
            }
        } catch (IOException ex) {
        }
    }).start();;
    if(!core.waitFor(5, TimeUnit.HOURS)) {
        isDestroyed = true;
        core.destroy();
    } else
        isDestroyed = false;

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