Using Python from within Java [duplicate]

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Java Python Integration

I have a large existing codebase written in 100% Java, but I would like to use Python for some new sections of it. I need to do some text and language processing, and I'd much rather use Python and a library like NLTK to do this.

I'm aware of the Jython project, but it looks like this represents a way to use Java and its libraries from within Python, rather than the other way round - am I wrong about this?

If not, what would be the best method to interface between Java and Python, such that (ideally) I can call a method in Python and have the result returned to Java?

Thank you.

Answer 1

Simply run the Python interpreter as a subprocess from within Java.

Write your Python functionality as a proper script, which reads from stdin and writes to stdout.

Use the Java Runtime class to spawn a subprocess that runs your Python script. This is very simple to do and provides a very clean interface.

---

Edit

import simplejson
import sys
for request in sys.stdin.readlines():
    args = simplejson.loads( request )
    result = myFunction( args['this'], args['that'] )
    sys.stdout.writeline( simplejson.dumps( result ) + "\n" )

The interface is simple, structured and very low overhead.

Answer 2

I'm aware of the Jython project, but it looks like this represents a way to use Java and its libraries from within Python, rather than the other way round - am I wrong about this?

Yes, you are wrong. You can either call a command line interpreter to run python code using Jyton or use python code from Java. In the past there was also a python-to-Java compiler, but it got discontinued with Jython 2.2

Answer 3

Remember to first check from those paying for the development that they're OK with the codebase needing a developer who knows both Python and Java from now on, and other cost and maintainability effects you've undoubtedly already accounted for.

See: http://www.acm.org/about/se-code 1.06, 2.03, 2.09, 4.03, 4.05, 6.07

Answer 4

Jython is a Python implementation running on the JVM. You can find information about embedding Python in an existing Java app in the user guide.

I don't know the environment that you're working in, but be aware that mixing languages in the same app can quickly lead to a mess. I recommend creating Java interfaces to represent the operations that you plan to use, along with separately-packaged implementation classes that wrap the Python code.

Answer 5

I don't think you could use NLTK from Jython, since it depends on Numpy which isn't ported to the JVM. If you need NLTK or any other native CPython extension, you might consider using some IPC mechanism to communicate between CPython and the JVM. That being said, there is a project to allow calling CPython from Java, called Jepp:

http://jepp.sourceforge.net/

The reverse (calling Java code from CPython) is the goal of JPype and javaclass:

sourceforge.net/projects/jpype/

pypi.python.org/pypi/javaclass/0.1

I've never used any of these project, so I cant't vow for their quality.

Answer 6

I would write a Python module to handle the text and language processing, and then build a small bridge in jython that your java program can interact with. The jython bridge will be a very simple one, that's really only responsible for forwarding calls to the python module, and return the answer from the python module to the java module. Jython is really easy to use, and setup shouldn't take you more than 15 minutes.

Best of luck!