Calling Java from Python

Question

What is the best way to call java from python   jython and RPC are not an option for me    I ve heard of JCC  http   pypi python org pypi JCC 1 9 a C   code generator for calling Java from C   Python But this requires compiling every possible call  I would prefer another solution   I ve hear about JPype  http   jpype sourceforge net   tutorial  http   www slideshare net onyame mixing-python-and-java  import jpype  jpype startJVM path to jvm dll   -ea    javaPackage   jpype JPackage  JavaPackageName    javaClass   javaPackage JavaClassName  javaObject   javaClass    javaObject JavaMethodName    jpype shutdownJVM      This looks like what I need  However  the last release is from Jan 2009 and I see people failing to compile JPype   Is JPype a dead project   Are there any other alternatives   Regards  David

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I m assuming that if you can get from C   to Java then you are all set  I ve seen a product of the kind you mention work well  As it happens the one we used was CodeMesh  I m not specifically endorsing this vendor  or making any statement about their product s relative quality  but I have seen it work in quite a high volume scenario   I would say generally that if at all possible I would recommend keeping away from direct integration via JNI if you can  Some simple REST service approach  or queue-based architecture will tend to be simpler to develop and diagnose  You can get quite decent perfomance if you use such decoupled technologies carefully

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Here is my summary of this problem  5 Ways of Calling Java from Python  http   baojie org blog 2014 06 16 call-java-from-python   cached   Short answer  Jpype works pretty well and is proven in many projects  such as python-boilerpipe   but Pyjnius is faster and simpler than JPype  I have tried Pyjnius Jnius  JCC  javabridge  Jpype and Py4j   Py4j is a bit hard to use  as you need to start a gateway  adding another layer of fragility

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I ve been integrating a lot of stuff into Python lately  including Java   The most robust method I ve found is to use IKVM and a C  wrapper   IKVM has a neat little application that allows you to take any Java JAR  and convert it directly to  Net DLL   It simply translates the JVM bytecode to CLR bytecode   See http   sourceforge net p ikvm wiki Ikvmc  for details   The converted library behaves just like a native C  library  and you can use it without needing the JVM   You can then create a C  DLL wrapper project  and add a reference to the converted DLL   You can now create some wrapper stubs that call the methods that you want to expose  and mark those methods as DllEport   See https   stackoverflow com a 29854281 1977538 for details   The wrapper DLL acts just like a native C library  with the exported methods looking just like exported C methods   You can connect to them using ctype as usual   I ve tried it with Python 2 7  but it should work with 3 0 as well   Works on Windows and the Linuxes  If you happen to use C   then this is probably the best approach to try when integrating almost anything into python

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If you re in Python 3  there s a fork of JPype called JPype1-py3  pip install JPype1-py3   This works for me on OSX   Python 3 4 3   You may need to export JAVA HOME  Library Java JavaVirtualMachines your-java-version   from jpype import   startJVM getDefaultJVMPath     -ea   java lang System out println  hello world   shutdownJVM

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Through my own experience trying to run some java code from within python i a manner similar to how python code runs within java code in python  I was unable to a find a straight forward methodology   My solution to my problem was by running this java code as beanshell scripts by calling the beanshell interpreter as a shell commnad from within my python code after editing the java code in a temporary file with the appropriate packages and variables   If what I am talking about is helpful in any manner  I am glad to help you sharing more details of my solutions

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I m on OSX 10 10 2  and succeeded in using JPype   Ran into installation problems with Jnius  others have too   Javabridge installed but gave mysterious errors when I tried to use it  PyJ4 has this inconvenience of having to start a Gateway server in Java first  JCC wouldn t install   Finally  JPype ended up working   There s a maintained fork of JPype on Github   It has the major advantages that  a  it installs properly and  b  it can very efficiently convert java arrays to numpy array  np arr   java arr      The installation process was   git clone https   github com originell jpype git cd jpype python setup py install   And you should be able to import jpype  The following demo worked   import jpype as jp jp startJVM jp getDefaultJVMPath     -ea   jp java lang System out println  hello world   jp shutdownJVM      When I tried calling my own java code  I had to first compile  javac   blah HelloWorldJPype java   and I had to change the JVM path from the default  otherwise you ll get inexplicable  class not found  errors    For me  this meant changing the startJVM command to   jp startJVM   Library Java JavaVirtualMachines jdk1 7 0 79 jdk Contents MacOS libjli dylib    -ea   c   jp JClass  blah HelloWorldJPype       Where my java class file is in   blah HelloWorldJPype class

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You could also use Py4J  There is an example on the frontpage and lots of documentation  but essentially  you just call Java methods from your python code as if they were python methods   from py4j java gateway import JavaGateway gateway   JavaGateway                            connect to the JVM java object   gateway jvm mypackage MyClass      invoke constructor other object   java object doThat   other object doThis 1  abc   gateway jvm java lang System out println  Hello World      call a static method   As opposed to Jython  one part of Py4J runs in the Python VM so it is always  up to date  with the latest version of Python and you can use libraries that do not run well on Jython  e g   lxml   The other part runs in the Java VM you want to call    The communication is done through sockets instead of JNI and Py4J has its own protocol  to optimize certain cases  to manage memory  etc    Disclaimer  I am the author of Py4J

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I m just beginning to use JPype 0 5 4 2  july 2011  and it looks like it s working nicely    I m on Xubuntu 10 04

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Pyjnius   Docs  http   pyjnius readthedocs org en latest   Github  https   github com kivy pyjnius  From the github page      A Python module to access Java classes as Python classes using JNI       PyJNIus is a  Work In Progress        Quick overview   gt  gt  gt  from jnius import autoclass  gt  gt  gt  autoclass  java lang System   out println  Hello world   Hello world   gt  gt  gt  Stack   autoclass  java util Stack    gt  gt  gt  stack   Stack    gt  gt  gt  stack push  hello    gt  gt  gt  stack push  world    gt  gt  gt  print stack pop   world  gt  gt  gt  print stack pop   hello

[java] Calling Java from Python

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