Thread: Input stream buffers up to 4K before available to read

Hi there,



I have a scenario where I want to read the input stream of a process(/usr/bin/program ran using java process builder) as soon as the program writes to stdout/console.
In general the program /usr/bin/program writes data to console/stdout as soon as there are bytes avaialble even with say 100 bytes. But the same program when I ran
using Java process builder and read the input stream, I do not get the data as soon as program writes to stdout/console but after 4K of data is available on the input stream.

I need the data(every byte written) to be available in the input stream in real time.

I have tried at least these two options. Any help would be greatly appreciated.

Option 1:
process = new ProcessBuilder().redirectErrorStream(true).command ("/usr/bin/ntfsubscribe", "-s").start();
InputStream is = process.getInputStream();
ReadableByteChannel channel = Channels.newChannel(is);
ByteBuffer buf = ByteBuffer.allocate(2048);

int bytesRead = channel.read(buf);
while (bytesRead != -1) {

System.out.println("Read " + bytesRead);
buf.flip();

while(buf.hasRemaining()){
System.out.print((char) buf.get());
}

buf.clear();
bytesRead = channel.read(buf);
}

Option 2:
BufferedReader input = new BufferedReader(new InputStreamReader(is));
String line = "";
while ((line = input.readLine()) != null) {

System.out.println(line);
}


Thanks

In my case, when the process first generated output of 1450 bytes it was not available in the input stream. It was in the
buffer and the process waited until the the next subsequent outputs adds upto 4k to produce output into inputstream. The process(/usr/bin/program)
generates the output when there is external trigger to it. Since after generating the first output, there was no external
trigger the first output was simply in the buffer but not yet available to the input stream to read. Hence, it is not real time and the first event is kind of lost on time.

Every output from the process is considering as an event on which some other process is started, some algorithm is run etc.

The output is the control data output not raw data output. Hence I need every data that is generated and which is less then 4k should
be immediately avaialble to the inputstream to read.

Hope I was able to clarifiy. I would be glad to have any technical work around to this if this is the behavior.

Yes I have tried directly reading the input stream in a separate thread and the same result.

Something like this in the thread run. I now have separate threads per input, output and error but no luck yet.
try {
int c;
String line = "";
while ((c = inputstream.read()) != -1) {
if (((char) c == '\r') || ((char) c == '\n')) {
if (!line.isEmpty())
System.out.println(line);
line = "";
} else
line += (char) c;
}
} catch (Throwable t) {
t.printStackTrace();
}