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Latrisha Adan
Firstly Do you only want to call functions or do you actually want Python code to change the data in your java objects? This is very important. If you only want to call some Python code with or without arguments, then that is not very difficult. If your arguments are primitives it makes it even more easy. However, if you want to have Java class implement member functions in Python, which change the data of the Java object, then this is not so easy or straight forward.
Secondly are we talking CPython, or will Jython do? I would say CPython is where its at! I would advocate this is why Python is so kool! Having such high abstractions however access to C or C++ when needed. Imagine if you could have that in Java. This question is not even worth asking if Jython is ok because then it is easy anyway.
Jython from Java is so easy, and if this is really enough then great. However it is very slow and no CPython! Is life worth living without CPython? I don't think so! You can easily have Python code implementing your member functions for you Java objects.
Pyro is the remote object module for Python. You have some object on a CPython interpreter, and you can send it objects which are transferred via serialization and it can also return objects via this method. Note that if you send a serialized Python object from Jython and then call some functions which change the data in its members, then you will not see those changes in Java. You just need to remember to send back the data which you want from Pyro. This, I believe, is the easiest way to get to CPython! You do not need any JNI or JNA or SWIG or .... You don't need to know any C, or C++. Kool huh?
OMG this method is not for the faint of heart. And I can tell you it has taken me very long to achieve this in with a decent method. Main reason you would want to do this is so that you can run CPython code which as full rein over you java object. There are major things to consider before deciding to try and breed Java (which is like a chimp) with Python (which is like a horse). Firstly if you crash the interpreter, that's lights out for you program! And don't get me started on concurrency issues! In addition, there is a lot of boiler, I believe I have found the best configuration to minimize this boiler but it is still a lot! So how to go about this:Consider that C++ is your middle man, your objects are actually C++ objects! Good that you know that now. Just write your object as if your program is in C++ and not Java, with the data you want to access from both worlds. Then you can use the wrapper generator called SWIG to make this accessible to java and compile a dll which you call (System.load(dllNameHere)) in Java. Get this working first, then move on to the hard part!To get to Python you need to embed an interpreter. Firstly I suggest doing some hello interpreter programs or this tutorial Embedding Python in C/C. Once you have that working, its time to make the horse and the monkey dance! You can send you C++ object to Python via [boost][3] . I know I have not given you the fish, merely told you where to find the fish. Some pointers to note for this when compiling.
When you compile boost you will need to compile a shared library. And you need to include and link to the stuff you need from jdk, ie jawt.lib, jvm.lib, (you will also need the client jvm.dll in your path when launching the application) As well as the python27.lib or whatever and the boost_python-vc100-mt-1_55.lib.Then include Python/include, jdk/include, boost and only use shared libraries (dlls) otherwise boost has a teary. And yeah full on I know. There are so many ways in which this can go sour. So make sure you get each thing done block by block. Then put them together.
It's not smart to have python code inside java. Wrap your python code with flask or another web framework to make it a microservice. This makes your java program able to call this microservice (e.g. via REST).
Several of the answers mention that you can use JNI or JNA to access cpython but I would not recommend starting from scratch because there are already open source libraries for accessing cpython from java. For example:
GraalVM is a good choice. I've done Java+Javascript combination with GraalVM for microservice design (Java with Javascript reflection). They recently added support for python, I'd give it a try especially with how big its community has grown over the years.
GraalVM provides a Python 3.8 compliant runtime. A primary goal of the GraalVM Python runtime is to support SciPy and its constituent libraries, as well as to work with other data science and machine learning libraries from the rich Python ecosystem. At this point, the Python runtime is made available for experimentation and curious end-users.
It depends on what do you mean by python functions? if they were written in cpython you can not directly call them you will have to use JNI, but if they were written in Jython you can easily call them from java, as jython ultimately generates java byte code.
Now when I say written in cpython or jython it doesn't make much sense because python is python and most code will run on both implementations unless you are using specific libraries which relies on cpython or java.
There are a number of differences. First, Jython programs cannot use CPython extension modules written in C. These modules usually have files with the extension .so, .pyd or .dll. If you want to use such a module, you should look for an equivalent written in pure Python or Java. Although it is technically feasible to support such extensions - IronPython does so - there are no plans to do so in Jython.
This gives a pretty good overview over the current options. Some of which are named in other answers. Jython is not usable until they decide to not implement Python 3. Many of the other projects are coming from the python side and want to access java. But there are a few options still, to name something which has not been named yet: gRPC
I have similar requirement, I think best solution is thrift for me(also a rpc solution), just run test passed successfully right now, and can use thrift-generator to gen thrift file from java interface, then gen python files and java client files from the thrift file
In in terms of data exchange from python to Java we can make it a rest services and exchange the data in the XML or Json format but sometimes we need to call automated script is easily created with python to called in java file.
Java 21 is chock-full of great features but that's for naught of you can't actually upgrade, so I've collected all potential upgrade hurdles and we'll go over every issue that you may encounter on the road from Java 17 to 21
Java 21 is chock-full of great features and if you're coming all the way from 17, there's a plethora of additions to use and get used to.From pattern matching to sequenced collections and countless API additions, from faster GC and overall performance improvements to better security, from virtual threads to better JFR and much, much more - you'll see improvements in all areas.And that's all great and in the coming weeks we'll tell you all about that in the "Road to 21" video series that you're currently watching the first episode of.
But it's all for naught if you can't actually update.And while there isn't one big hurdle, there are plenty of small ones that may cause hiccups when you're moving your project to Java 21.So to make sure that you can hit the ground running, I've collected them all and we'll go over every issue that you may encounter on the road from Java 17 to 21, although I'm sure most of you will only see a tiny fraction.
We'll cover changes in existing APIs that may require you to update your code, ongoing deprecations, and who better to do that than Dr. Deprecator himself, changes in networking and encoding, runtime and tools.If you want to follow up on any of this, there are plenty of links in the description.But we'll also go beyond the nitty-gritty details and see the bigger picture of how to best prepare and execute your Java and 3rd party updates.
We'll get to that, Jose, but we also need to let people know that the introduction of these new interfaces may lead to conflicts with external implementations of the collection interfaces.So if you or your dependencies contain any of those, be aware that you may encounter method naming conflicts or issues with covariant overrides and type inference.
First, Double.toString() and Float.toString() now correctly determine the smallest number of digits that still uniquely distinguish the float or double from its adjacent float or double.So, for example, calling Double.toString(1e23) will now print "1.0E23" instead of 9.a-lot-of-ninesE22.
The other change concerns IdentityHashMap.Its methods remove(key, value) and replace(key, value, newValue) erroneously compared value arguments to the values in the map with equals even though it's the identity hash map.So that's been fixed, which might mean that code now removes and replaces fewer elements than it used to.
First, let's start off with the Thread API:The Thread.stop, Thread.suspend, and Thread.resume APIs have now been changed, so that they unconditionally throw UnsupportedOperationException.They don't actually operate on the target thread.We've made those changes to make room for Loom's virtual threads.If your application uses any of those Thread APIs, you're gonna have to change it.We also made some changes to the bulk operations on ThreadGroup.
Another area to keep your eye on is the security manager.It was deprecated for removal in JDK 17.One change you'll need to make in JDK 21 is to make sure to set the java.security.manager property to allow, in order for your application to call the setSecurityManager API.
Another change we're contemplating is, even in the future, after we removed the security manager, are we still going to have the getSecurityManager API return null.Most things that use security features only do the check permissions test if getSecurityManager returns non-null.
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