convert openAPI specification to a Postman collection using java/spring boot

In java you can run node script as a shell command and read output from it.

1. First create new node project with npm init command.

2. Create index.js file and add the following code. I have modified your code to get input from command line arguments instead of reading from a file.

var Converter = require('openapi-to-postmanv2')
openapiData = process.argv[2]

Converter.convert({ type: 'string', data: openapiData },
    {}, (err, conversionResult) => {
        if (!conversionResult.result) {
            console.log('Could not convert', conversionResult.reason);
        }
        else {
            console.log(conversionResult.output[0].data);
        }
    }
);

3. Create App.java and add following lines.

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class App {
    public static void main(String[] args) throws InterruptedException, IOException {
        String data = "YOUR_DATA_HERE";
        String command = String.format("node index.js \"%s\"", data);
        Runtime runtime = Runtime.getRuntime();
        Process pr = runtime.exec(command);
        pr.waitFor();
        BufferedReader reader = new BufferedReader(new InputStreamReader(pr.getInputStream()));
        String output = "";
        String line;
        while ((line = reader.readLine()) != null) {
            output += line;
        }
        System.out.println(output);
    }
}

4. Compile and run it.

javac App.java
java App

Please note that this is a very minimalist example. You could use standard Error Stream to read errors in your application.