Java - How to call python classes using processbuilder

Question

How do I call and execute python class methods from java. My current java code works, but only if I write:

if __name__ == '__main__':
    print("hello")

But I want to execute a class method, regardless of if __name__ == '__main__':

Example python class method I would like to run:

class SECFileScraper:
    def __init__(self):
        self.counter = 5

    def tester_func(self):
        return "hello, this test works"

Essentially I would want to run SECFileScraper.tester_func() in java.

My Java code:

try {

            ProcessBuilder pb = new ProcessBuilder(Arrays.asList(
                    "python", pdfFileScraper));
            Process p = pb.start();

            BufferedReader bfr = new BufferedReader(new InputStreamReader(p.getInputStream()));
            String line = "";
            System.out.println("Running Python starts: " + line);
            int exitCode = p.waitFor();
            System.out.println("Exit Code : " + exitCode);
            line = bfr.readLine();
            System.out.println("First Line: " + line);
            while ((line = bfr.readLine()) != null) {
                System.out.println("Python Output: " + line);


            }

        } catch (Exception e) {
            e.printStackTrace();
        }

pdfFileScraper is the file path to my python script.

I've tried jython, but my python files use pandas and sqlite3, which can't be implemented using jython.

Answer 1

So if I understand your requirement, you want to invoke a class method in pdfFileScraper.py. The basics of doing this from the shell would be something akin to:

scraper=path/to/pdfFileScraper.py
dir_of_scraper=$(dirname $scraper)
export PYTHONPATH=$dir_of_scraper
python -c 'import pdfFileScraper; pdfFileScraper.ClassInScraper()'

What we do is get the directory of pdfFileScraper, and add it to the PYTHONPATH, then we run python with a command that imports the pdfFileScraper file as a module, which exposes all the methods and classes in the class in the namespace pdfFileScraper, and then construct a class ClassInScraper().

In java, something like:

import java.io.*;
import java.util.*;

public class RunFile {
    public static void main(String args[]) throws Exception {
        File f = new File(args[0]); // .py file (e.g. bob/script.py)

        String dir = f.getParent(); // dir of .py file
        String file = f.getName(); // name of .py file (script.py)
        String module = file.substring(0, file.lastIndexOf('.'));
        String command = "import " + module + "; " + module + "." + args[1];
        List<String> items = Arrays.asList("python", "-c", command);
        ProcessBuilder pb = new ProcessBuilder(items);
        Map<String, String> env = pb.environment();
        env.put("PYTHONPATH", dir);
        pb.redirectErrorStream();
        Process p = pb.start();

        BufferedReader bfr = new BufferedReader(new InputStreamReader(p.getInputStream()));
        String line = "";
        System.out.println("Running Python starts: " + line);
        int exitCode = p.waitFor();
        System.out.println("Exit Code : " + exitCode);
        line = bfr.readLine();
        System.out.println("First Line: " + line);
        while ((line = bfr.readLine()) != null) {
            System.out.println("Python Output: " + line);
        }
    }
}