Running Python scripts in Java

Question

I'm trying to run a python script during the execution of my java code, because it will depend on the output received from the python script. So far I've tried using jythonc, unfortunately to no success, and now im trying to use the java Runtime and java Process to execute the python script.

Now I've run into a problem when trying to call the python script. I feel as though it doesn't even call the script because it takes less than a couple seconds to get to the next page....

Could the problem be how I am calling the python script?? I am trying to run this through a web application...

Here is some of my code:

    String run = "cmd /c python duplicatetestingoriginal.py" ;

    boolean isCreated = fwr.writeFile(BugFile, GD, 500, true, 5, "LET");

    if(isCreated){
        try{
            r = Runtime.getRuntime();
            p = r.exec(run);
            BufferedReader stdInput = new BufferedReader(new InputStreamReader(p.getInputStream()));
    BufferedReader stdError = new BufferedReader(new InputStreamReader(p.getErrorStream()));

    String line = "";
    while ((line = stdInput.readLine()) != null) {
                System.out.println(line);
    }
    while ((line = stdError.readLine()) != null) {
               errorW.write(line);
    }

            int exitVal = p.waitFor();
            arrayList = fwr.readResults();
        }catch(Exception e){

        }
    }
    else{
        // troubleshoot....

    }

You're running under Windows, yes? Is 'python' on your PATH? What happens if you type cmd /c python duplicatetestingoriginal.py into Start -> Run...? — Managu
– Managu, Commented Jan 25, 2012 at 16:51
You also might want to reconsider how you're reading stdInput/stdError. See "When Runtime.exec won't": javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html — Managu
– Managu, Commented Jan 25, 2012 at 16:52
Yes i am running in Windows, and python is in my PATH. The code runs when i type it into the cmdline or Run — Shahab
– Shahab, Commented Jan 25, 2012 at 16:52
Could it possibly be the case that duplicatetestingoriginal.py isn't in the current directory when you run the Java code? Maybe put in the full absolute path there? — Managu
– Managu, Commented Jan 25, 2012 at 16:55
Another thought: you catch (Exception e) and then drop it. Maybe an Exception is being thrown? Couldn't hurt to add a e.printStackTrace(); while debugging. — Managu
– Managu, Commented Jan 25, 2012 at 16:56

ekstrakt · Accepted Answer · 2012-04-06 16:54:09Z

Instead of String for the command, split it to chunks and make a String[]. No need to state cmd /c, I think.

This is a sample code from my application:

//Running on windows
command = new String[4];
command[0]=directory.getCanonicalPath()+"/data/ExtenalApp.exe"; //extenal commandline app, not placed in path, but in subfolder
command[1]=directory.getCanonicalPath()+"/data/SomeFile.txt"; //file needed for the external app, sent as an argument
command[2]=arg1; //argument for the app
command[3]=arg2; //argument for the app

//Running on Mac
command = new String[6];
command[0]="python";
command[1]=directory.getCanonicalPath()+"/data/wp.py"; //path to the script
command[2]="-F"; //argument/Flag/option
command[3]="--dir="+path; //argument/option
command[4]="--filename="+filename; //argument/option 
command[5]=argument; //argument/option


Process process = Runtime.getRuntime().exec(command);
process.waitFor();
process.destroy();

I don't handle the Input/Output streams because the script/app doesn't require input, and outputs only when finished, nothing important. Which might not be the case for you.

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