Jynx 0.2 released

I’ve released Jynx 0.2. Jynx is a Jython package which utilizes dynamic Java compilation from Jython and improves on Java scripting. With Jynx 0.2 two major new features are implemented now.

Annotation Extraction

In the initial Jynx 0.1 release an annotation object was defined which can be used as a decorator. A Python class such as

@JavaClass
class TestClass(Object):
    @annotation("Test")
    @signature("public void _()")
    def test_report_test_failure(self):
        assertTrue("length of empty list is 0", len([]) != 0)

equipped with the JavaClass decorator is compiled into a Java class on the fly which acts as a proxy for a Python object and provides the correct interface for being used within a Java framework which expects methods of a particular type signature and annotations. The class defined above can be used within JUnit 4.X.

Jynx 0.2 provides a new classmethod extract of the annotation class which can be used to extract Java annotation classes and acts as a factory function for Jython annotation objects.

# import Test annotation in JUnit 4.X
from org.junit import Test      
 
# a Python annotation object
Test = annotation.extract(Test) 
 
# keep a signature object as a parameter and returns a new Jython
# annotation object. The Java code generator will create a method
# with the correct signature and the @Test annotation
Test = Test(signature("public void _()")  
 
@JavaClass
class TestClass(Object):
    @Test
    def test_report_test_failure(self):
       assertTrue("length of empty list is 0", len([]) != 0)

As we see there is no overhead left here. When programming against a Java API / framework, Jython annotations can be defined within a single file and used application wide.

Classpath Manipulation

For reasons which are not completely transparent to me Java doesn’t permit runtime classpath manipulations. The JDK defines an addURL method in a special classloader called URLClassLoader. This method is protected and cannot generally be accessed without reflection. Internally the Sun JVM uses such a loader class ( or a subclass of it ) and when you are willing to accept a hack and programming against an implementation detail you can use the JVMs default class loader and add new paths to a classpath:

from java.lang import ClassLoader
systemLoader = ClassLoader.getSystemClassLoader()
systemLoader.addURL("file:///C|junit-4.6.jar")

Jynx defines a ClassPath class and a new sys module attribute classpath. Adding a file system path P to sys.classpath results in a method call

systemloader.addURL(URL("file:"+pathname2url(pth)))

which converts the file system path into a Java URL object and adds it to the classpath. Additionally the same path is added to the PYTHONPATH via sys.path:

sys.classpath.append(r"C:\junit-4.6.jar")

The advantage is that each Python package can maintain the Java packages it depends upon and no global CLASSPATH environment variable has to be adapted unless a Java or Jython class defines its own class loader.

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