Embed Jython to Your Java Codebase

Jython is a great tool for some quick Java scripts using a pretty solid syntax. Actually, it works wonderfully when it comes to implementing some maintenance or monitoring scripts with

If you work with other teams that have a Python background, it makes absolute sense to integrate Python to your Java applications.

First, let’s import the Jython interpreter using the standalone version.

group 'com.gkatzioura'
version '1.0-SNAPSHOT'

apply plugin: 'java'

sourceCompatibility = 1.5

repositories {
    mavenCentral()
}

dependencies {
    testCompile group: 'junit', name: 'junit', version: '4.11'
    compile group: 'org.python', name: 'jython-standalone', version: '2.7.0'
}

The easiest thing to do is just to execute a Python file in our class path. The file would be hello_world.py

 print "Hello World" 

And then pass the file as an inputstream to the interpeter

package com.gkatzioura;

import org.python.core.PyClass;
import org.python.core.PyInteger;
import org.python.core.PyObject;
import org.python.core.PyObjectDerived;
import org.python.util.PythonInterpreter;

import java.io.InputStream;

/**
 * Created by gkatzioura on 19/10/2016.
 */
public class JythonCaller {

    private PythonInterpreter pythonInterpreter;

    public JythonCaller() {
        pythonInterpreter = new PythonInterpreter();
    }

    public void invokeScript(InputStream inputStream) {

        pythonInterpreter.execfile(inputStream);
    }

}

 @Test public void testInvokeScript() { InputStream inputStream = this.getClass().getClassLoader().getResourceAsStream("hello_world.py"); jythonCaller.invokeScript(inputStream); } 

The next step is to create a Python class file and another Python file that will import the class file and instantiate a class.

The class file would be divider.py.

class Divider:

    def divide(self,numerator,denominator):

        return numerator/denominator;

And the file importing the Divider class would be classcaller.py

from divider import Divider

divider = Divider()

print divider.divide(10,5);

So let us test it

@Test
public void testInvokeClassCaller() {

    InputStream inputStream = this.getClass().getClassLoader().getResourceAsStream("classcaller.py");
    jythonCaller.invokeScript(inputStream);
} 

What we can understand from this example is that the interpreter successfully imports the files from the classpath.

Running files using the interpreter is OK, however, we need to fully utilize classes and functions implemented in Python.

Therefore, the next step is to create a Python class and use its functions using Java.

package com.gkatzioura;

import org.python.core.PyClass;
import org.python.core.PyInteger;
import org.python.core.PyObject;
import org.python.core.PyObjectDerived;
import org.python.util.PythonInterpreter;

import java.io.InputStream;

/**
 * Created by gkatzioura on 19/10/2016.
 */
public class JythonCaller {

    private PythonInterpreter pythonInterpreter;

    public JythonCaller() {
        pythonInterpreter = new PythonInterpreter();
    }

    public void invokeClass() {

        pythonInterpreter.exec("from divider import Divider");
        PyClass dividerDef = (PyClass) pythonInterpreter.get("Divider");
        PyObject divider = dividerDef.__call__();
        PyObject pyObject = divider.invoke("divide",new PyInteger(20),new PyInteger(4));

        System.out.println(pyObject.toString());
    }

}

You can find the source code on GitHub.