I have a Java app that takes a long time to be initialized (so I can't use a command-line like interface) and I need to pass text and receive the output of a Java method from Python. Is it possible to load the Java application, have it open all the time the Python script runs and use a method from that app?
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1If you are running Jython it is easyRomain Hippeau– Romain Hippeau2010-05-03 15:48:43 +00:00Commented May 3, 2010 at 15:48
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+1 for Jython. It's seamless to use Java from within the Jython interpreter.gpampara– gpampara2010-05-03 16:34:39 +00:00Commented May 3, 2010 at 16:34
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4 Answers
I don't think the use of Python helps all that much over a command line (at least not a *nix command line), but the basic idea is to communicate over a socket or some similar mechanism. That means that the Java application will have to be wrapped in some code which opens a socket and waits for the python script to contact it. If you are most comfortable with python, you could look to implement that wrapper in Jython.
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I've used JPype for something similar and it worked great.
JPype is an effort to allow python programs full access to java class libraries. This is achieved not through re-implementing Python, as Jython/JPython has done, but rather through interfacing at the native level in both Virtual Machines.
If the java app is running you should also consider xml-rpc as it also works well.
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Py4J is a way to call Java from a python script. Here is the project website: http://py4j.sourceforge.net/
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[ Disclaimer: I am the primary maintainer of PJRmi ]
PJRmi is one of the libraries which provides support for calling into Python; others are:
py4j allows Python to call into Java. It also supports Java calling back into Python so that Python clients can implement Java interfaces. It works by communicating over a socket.
jpy is another in-process implementation. One of its key features is support for fast pass-by-value operations with arrays by use of pointer hand-off.
jpype is another in-process implementation. Since it also uses internal C-based handoff it's highly performant.
PyJNIus is another implementation which accesses Java classes using JNI.
A simple example of calling into Java from Python, where the Java process is long-lived, would look like:
>>> import pjrmi
>>> c = pjrmi.connect_to_child_jvm()
>>> HashMap = c.javaclass.java.util.HashMap
>>> m = HashMap(dict((str(i), i+1) for i in range(5)))
>>> m.get("3")
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Which one of the various versions of the Python/Java bridges you like depends upon your use-case. Ones which use direct JNI for hand-off (like JPype) tend to be very fast but might limit you to a single Java instance per invocation.
