Module for dynamically loading Java Classes using the import system.
This is a replacement for the jpype.JPackage(“com”).fuzzy.Main type syntax. It features better safety as the objects produced are checked for class existence. To use java imports, import the domains package prior to importing a java class.
This module supports three different styles of importing java classes.
1) Import of the package path¶
Importing a series of package creates a path to all classes contained in that package. It does not provide access the the contained packages. The root package is added to the global scope. Imported packages are added to the directory of the base module.
import java.lang # Adds java as a module import java.util mystr = java.lang.String('hello') mylist = java.util.LinkedList() path = java.nio.files.Paths.get() # ERROR java.nio.files not imported
2) Import of the package path as a module¶
import <java_package> as <var>
A package can be imported as a local variable. This provides access to all java classes in that package. Contained packages are not available.
import java.nio as nio bb = nio.ByteBuffer() path = nio.file.Path() # ERROR subpackages file must be imported
3) Import a class from an object¶
from <java_package> import <class>[,<class>*] [as <var>]
An individual class can be imported from a java package. This supports inner classes as well.
# Import one class from java.lang import String mystr = String('hello') # Import multiple classes from java.lang import Number,Integer,Double # Import java inner class java.lang.ProcessBuilder.Redirect from java.lang.ProcessBuilder import Redirect
This method can also be used to import a static variable or method from a class.
Wild card Imports¶
Wild card imports for classes will import all static method and fields into the global namespace. They will also import any inner classes that have been previously be accessed.
Wild card importation of package symbols are not currently supported and have unpredictable effects. Because of the nature of class loaders it is not possible to determine what classes are currently loaded. Some classes are loaded by the boot strap loader and thus are not available for discovery.
As currently implemented [from <java_package> import *] will import all classes and static variables which have already been imported by another import call. As a result which classes will be imported is based on the code pat and thus very unreliable.
It is possible to determine the classes available using Guava for java extension jars or for jars specifically loaded in the class path. But this is sufficiently unreliable that we recommend not using wildcards for any purpose.
Occasionally a java class may contain a python keyword. Python keywords as automatically remapped using trailing underscore.
from org.raise_ import Object => imports "org.raise.Object"
Controlling Java package imports¶
By default domains imports four top level domains (TLD) into the python import system (com, gov, java, org). Additional domains can be added by calling registerDomain. Domains can be an alias for a java package path.
domains.registerDomain('jname') from jname.framework import FrameObject domains.registerDomain('jlang', alias='java.lang') from jlang import String
- Wildcard imports are unreliable and should be avoided. Limitations in the Java specification are such that there is no way to get class information at runtime. Python does not have a good hook to prevent the use of wildcard loading.
- Non-static members can be imported but can not be called without an instance. Jpype does not provide an easy way to determine which functions objects can be called without an object.