3 ways to execute python scripts in java (Including 3rd party packages)

If you want to execute some piece of python script code in your java programm, you may have two good options to achieve this.

One is "javax.script" , the other is "jython"

Both of them could open a python intepreter in your programm,  and execute python script.

 

1. javax.script

import javax.script.ScriptEngineManager;
import javax.script.ScriptEngine;

public class RunPythonScriptSample {
    public static void main(String[] args) {
        //
        // Creating an instance of ScriptManager. With ScriptManager in hand we
        // can create an interpreter or ScriptEngine to run JavaScript.
        //
        ScriptEngineManager manager = new ScriptEngineManager();
        
        //
        // Calling manager.getEngineByExtension("js") returns a ScriptEngine
        // implementation for python.
        //
        ScriptEngine engine = manager.getEngineByExtension("python");

        //
        // Do something with the script engine.
         engine.eval("import os");
        //......
    }
}


 



2 Jython


jython is java implementation of python. In this approach, you need to install jython, then from the build package, find out jython.jar.

Import this jar to your project. We need to use  classes e.g "org.python.util.PythonInterprete" in this jar.



import org.python.util.PythonInterpreter; 
import org.python.core.*; 

public class SimpleEmbedded { 
    public static void main(String []args)
	throws PyException
    { 
	PythonInterpreter interp =
	    new PythonInterpreter();//open a python interpreter

	System.out.println("Hello, brave new world");
	interp.exec("import sys");//execute python script 
	interp.exec("print sys");

	interp.set("a", new PyInteger(42));
	interp.exec("print a");
	interp.exec("x = 2+2");
	PyObject x = interp.get("x");

	System.out.println("x: "+x);
	System.out.println("Goodbye, cruel world");
    }
}


 

See also : http://jythonpodcast.hostjava.net/jythonbook/chapter10.html



3. If you just want to execute a python script file. You can use Runtime.exec() to fork a process and execute the command.

The key point of these approach is "Set correct environment variables to JVM"



Below is a example. 

What's more in this example? Standard output stream - stdout in python script will be redirect to java inputstream, this is extremly 

useful when you want to retrieve data / check the result from the python script.



import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Vector;

public class RunPythonScipt {

	/**
	 * Run pyJaql test script- "test.py" 
	 * Test result will be recorded in "testl.log" 
	 */
	public void runl() {

		Process proc = null;
		Runtime runtime = Runtime.getRuntime();
		List<String> list = new Vector<String>();
		Map<String, String> sysenv = System.getenv();// get system environment
		// variables
		Iterator<String> it = sysenv.keySet().iterator();
		while (it.hasNext()) {
			String key = it.next();
			list.add(key + "=" + sysenv.get(key));// add system environment
			// variables to JVM runtime
			// variables
		}
		String[] env = new String[list.size()];
		System.arraycopy(list.toArray(), 0, env, 0, list.size());
		try {
			proc = runtime.exec("test.py",env);// execute test script
		} catch (IOException e) {
			e.printStackTrace();
		}
		InputStream stdin = proc.getInputStream();
		InputStreamReader isr = new InputStreamReader(stdin);
		BufferedReader br = new BufferedReader(isr);
		String line = null;
		String result = null;
		try {
			// record the test result in "test.log"
			BufferedWriter recorder = new BufferedWriter(new FileWriter("test.log"));
			while ((line = br.readLine()) != null) {
				recorder.write(line + "/n");
			}
			recorder.close();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

}