Hide jpy from Python users

[jjbrosnan]

In our documentation, we have some instances of Python code that uses jpy to call Java from Python. We've begun to add some functionalities to the deephaven module that allow a user to call java without using jpy. One area that isn't covered, though, is importing Java packages in Python.

Currently, it's extremely diffieult (if not impossible) to implement the analogue of the following code in Python:

ClassLoader.getSystemClassLoader().addURL(new URL(URL_to_jar))

The closest you can get in Python is:

import jpy
URL = jpy.get_type("java.net.URL")
URLClassLoader = jpy.get_type("java.net.URLClassLoader")
jar_url = URL(URL_to_jar)
URL_array = jpy.array(URL, [jar_url])
cryptocompare_classloader = URLClassLoader(URL_array)

This, however, creates a URLClassLoader, but does not get the System ClassLoader. Attempting to call getSystemClassLoader() returns a java.lang.ClassLoader, which does not have an addURL() method.

If a user wants to use an external Java package in a Python console for some reason, they can't. It would be pretty nice to have a little java method that can be called from Python to make this easy for a Python user.

[jmao-denver]

@chipkent I am puzzled that this is slated for May delivery. I talked to @jjbrosnan to learn more about it and he suggested that I reach out to you to see if there is a concrete use case that could demo this is something we absolutely need to provide. Your thoughts?

[chipkent]

1. I don't think this is a May deliverable.
2. I think this stuff gets fixed by Make Python import Java types using import #1525.
3. I think the example above can be made to work using jpy.get_type('java.lang.ClassLoader'), so that the python is just like the Java. @jjbrosnan