Question

I have a piece of code that invokes an instance of the bash terminal through the use of the following —

proc = Runtime.getRuntime().exec("/bin/bash", null, working-dir);

and then to run unix commands on this invoked instance of bash I’m using a PrintWriter object like this —

PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(proc.getOutputStream())), true);

I’m then using the PrintWriter object to actually execute the commands in the following fashion–

out.println("pwd");
out.println("ls >a.txt");

While both of the commands seem to work perfectly fine, I have an issue in the case wherein I construct a command based on some user input. Being specific, I’m constructing a command to send some files to a printer on the network and I’m doing it like this —

while ((strLine = br.readLine()) != null)   {
cmd= blah +blah +blah;//Construction of the command
out.println(cmd);
}

What is actually happening in the above piece of code is that br is reading from a file which contains all the files that need to be printed and then the string having the file name goes into the command and I write it onto the PrintWriter object.

the issue Im facing is that , I guess there some sort of queuing that’s happening and the PrintWriter object is not actually passing on the command to the invoked bash instance every time a command is constructed.
So at the end of the day, if there are 40 commands that are being constructed, only about 16-18 documents are being printed.
I guess it it because it is sending all the commands to the printer in one go resulting in the loss.I want to eliminate this loss.

Any pointers ??

Thanks
p1nG

Answer 1

Try putting an out.flush() in your loop. This will flush the buffer in the BufferedWriter that you created.

Another tip may be to avoid trying use a single bash exec for all of the commands and instead construct and execute the command individually. Consider using Process Builder instead of Runtime.exec().