Running a .py file from Java

I am trying to execute a .py file from java code. I move the .py file in the default dir of my java project and I call it using the following code:

    String cmd = "python/";
    String py = "file";
    String run = "python  " +cmd+ py + ".py";
    System.out.println(run);
    //Runtime.getRuntime().exec(run);

    Process p = Runtime.getRuntime().exec("python  file.py");

Either using variable run, or the whole path or "python file.py" my code is running showing the message build successful total time 0 seconds without execute the file.py. What is my problem here?

You can use like this also:

String command = "python /c start python path\to\script\script.py";
Process p = Runtime.getRuntime().exec(command + param );

or

String prg = "import sys";
BufferedWriter out = new BufferedWriter(new FileWriter("path/a.py"));
out.write(prg);
out.close();
Process p = Runtime.getRuntime().exec("python path/a.py");
BufferedReader in = new BufferedReader(new InputStreamReader(p.getInputStream()));
String ret = in.readLine();
System.out.println("value is : "+ret);

Run Python script from Java

I believe we can use ProcessBuilder

Runtime.getRuntime().exec("python "+cmd + py + ".py");
.....
//since exec has its own process we can use that
ProcessBuilder builder = new ProcessBuilder("python", py + ".py");
builder.directory(new File(cmd));
builder.redirectError();
....
Process newProcess = builder.start();

String command = "cmd /c python <command to execute or script to run>";
    Process p = Runtime.getRuntime().exec(command);
    p.waitFor();
    BufferedReader bri = new BufferedReader(new InputStreamReader(p.getInputStream()));
    BufferedReader bre = new BufferedReader(new InputStreamReader(p.getErrorStream()));
          String line;
        while ((line = bri.readLine()) != null) {
            System.out.println(line);
          }
          bri.close();
          while ((line = bre.readLine()) != null) {
            System.out.println(line);
          }
          bre.close();
          p.waitFor();
          System.out.println("Done.");

    p.destroy();