No error or output when C++ executable is run from Java

Question

I am trying to run a c++ executable from my Java web application. When I go the relevant page it executes the commands and runs the executable but does not produce any output.

Here is my code:

URL createWav = QRcodeController.class.getClassLoader().getResource("createWav");
log.info("The path of the c++ executable obtained: "+ createWav.getPath());
Process p1 = Runtime.getRuntime().exec("chmod 777 " + createWav.getPath());
p1.waitFor();
int exitVal=1;
try {
        Process p2 = Runtime.getRuntime().exec(createWav.getPath(), args);
        exitVal = p2.waitFor();
}
catch (Exception e)
{
    log.error(e.getStackTrace());
}
if(exitVal == 1)
    throw new Exception("Error in c++ program");

It does not throw any error so the c++ program runs fine but it does not produce the file it is supposed to. When I run the same command from the command line in the same machine it works perfectly producing the required file. I am not sure what I am doing wrong.

Could you retry this with a hard coded path? It might be that the file is being created by the Java program but in a different place. — Stefan
– Stefan, Commented Jun 28, 2012 at 10:40
It was not able to run the program so that is why I could not find the file. Thanks. — ishan
– ishan, Commented Jun 29, 2012 at 6:17

Denys Séguret · Accepted Answer · 2012-06-28 10:40:58Z

2

Get the output stream and the error stream from the process to see what happens.

Now you're working blindly.

answered Jun 28, 2012 at 10:40

Denys Séguret

384k90 gold badges813 silver badges780 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

ishan Over a year ago

Thanks I am able to see the output now and currently onto debugging it. Thanks for the help.

MvG · Accepted Answer · 2012-06-28 11:04:03Z

1

The C++ program is writing its output to a pipe, not the standard output of the Java program. Use Process.getOutputStream() to access that stream or, with Java 1.7, employ a ProcessBuilder where you can use redirectOutput like this:

pb.redirectOutput(ProcessBuilder.Redirect.INHERIT)

In case your C++ program might write things to its standard error stream, you should probably deal with that in the same way.

Also note that leaving either of these streams connected to a pipe and not reading from that pipe might cause your application to block on output if the buffer associated with the pipe becomes full. To simply ignore output, you'd have to explicitely redirect it to /dev/null. That's not your aim just now, but it might be in a different situation.

edited Jun 28, 2012 at 11:04

answered Jun 28, 2012 at 10:47

MvG

61.8k25 gold badges158 silver badges294 bronze badges

Collectives™ on Stack Overflow

No error or output when C++ executable is run from Java

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related