controlling a java program from another

Question

I want to run a Java program from another using ProcessBuilder

I used the code

Process pr = rt.exec("cmd /c cd C:\\Users\\naman\\Desktop & java CalculateSum");
BufferedReader input = new BufferedReader(new InputStreamReader(pr.getInputStream()));
BufferedReader error = new BufferedReader(new InputStreamReader(pr.getErrorStream()));
BufferedWriter output= new BufferedWriter(new OutputStreamWriter(pr.getOutputStream()));
String line = null;

while ((line = input.readLine()) != null) {
    System.out.println(line);
}

output.write("10");
output.write("30");

while ((line = input.readLine()) != null) {
    System.out.println(line);
}

int exitVal = pr.waitFor();
System.out.println("Exited with error code " + exitVal);

CalculateSum has following code:

System.out.print("Enter 1 st value : ");
a=Integer.parseInt(br.readLine());
System.out.print("\nEnter second number : ");
b=Integer.parseInt(br.readLine());
System.out.println("\nresult is : "+(a+b));

My basic motivation is to run a Java program from another Java program.

NOTE: I don't want to use command line arguments to take input. Also I have tried using ProcessBuilder for the same purpose, but that also did not work.

What is the question? Please add actual question to the... question. — hyde
– hyde, Commented Dec 4, 2012 at 12:36
Run a Java program using another Java program!!?? What for dude ? What are you trying to achieve ? — sakthisundar
– sakthisundar, Commented Dec 4, 2012 at 12:37

Markus · Accepted Answer · 2012-12-07 13:22:29Z

1

You could use ExpectJ (http://expectj.sourceforge.net/) to talk to another program using standard input/output.

Use this instead of trixing with BufferedReader/BufferedWriter in your first code block:

ExpectJ expectinator = new ExpectJ(5);
Spawn shell = expectinator.spawn("cmd /c cd C:\\Users\\naman\\Desktop & java CalculateSum");

// Talk to it
shell.expect("Enter 1 st value");
shell.send("10\n");
shell.expect("Enter second value");
shell.send("30\n");

edited Dec 7, 2012 at 13:22

answered Dec 4, 2012 at 12:47

Markus

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3 Comments

Naman Kapoor Over a year ago

In the example given above, I have the source code so I can edit it with expectj.sourceforge.net But in reality I don't have the source code. All I have is the code to access another program.

Markus Over a year ago

Wait, what code do you have? The client (first in your question) or CalculateSum?

Markus Over a year ago

So, what I suggested was to use ExpectJ in the first code block (see edit), not the second (which was CalculateSum). I think it could really work!

hyde · Accepted Answer · 2012-12-04 12:40:55Z

0

Just blindly guessing at what the issue is, the problem may be flushing.

Try adding System.out.flush(); after each print in the CalculateSum.

In the first program, add newline to your output.write calls, such as output.write("10\n");, and also output.flush(); after that.

answered Dec 4, 2012 at 12:40

hyde

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