After searching for an option to run Java code from Django application(python), I found out that Py4J is the best option for me. I tried Jython, JPype and Python subprocess and each of them have certain limitations:

• Jython. My app runs in python.
• JPype is buggy. You can start JVM just once after that it fails to start again.
• Python subprocess. Cannot pass Java object between Python and Java, because of regular console call.

On Py4J web site is written:

In terms of performance, Py4J has a bigger overhead than both of the previous solutions (Jython and JPype) because it relies on sockets, but if performance is critical to your application, accessing Java objects from Python programs might not be the best idea.

In my application performance is critical, because I'm working with Machine learning framework Mahout. My question is: Will Mahout also run slower because of Py4J gateway server or this overhead just mean that invoking Java methods from Python functions is slower (in latter case performance of Mahout will not be a problem and I can use Py4J).

JPype issue that @HIP_HOP mentioned with JVM getting detached from new threads can be overcome with the following hack (add it before the first call to Java objects in the new thread which does not have JVM yet):

# ensure that current thread is attached to JVM
# (essential to prevent JVM / entire container crashes 
# due to "JPJavaEnv::FindClass" errors)
if not jpype.isThreadAttachedToJVM():jpype.attachThreadToJVM()