Re: [Jython-dev] generating javaclasses from jython in runtime.

[Oti <oh...@ya...>]

[ Morten Wilken ]

> 1) have some python code in a file.
> 2) at runtime, read the file and put the code in a class that
> implements a
> java interface
> 3) comple the class and let the jvm load it, so i could use it as a
> normal
> class.

Morten,
please find an example below. Hopefully it is what you were looking
for.
The java interface:

 package test;

 public interface MyInterface {
   public Number getNumber(String start);
 }

The small.py file containing a class implementing the java interface
(should be on python.path):

 from test import MyInterface
 from java.lang import Integer
 class implementation(MyInterface):
   def getNumber(self, start):
     return Integer(len(start))

A java class to get instances of the implementation:

 package test;

 import org.python.core.Py;
 import org.python.core.PyObject;
 import org.python.core.PySystemState;
 import org.python.core.imp;

 public class MyInterfaceFactory {
   private PyObject _classObject;
   
   public MyInterfaceFactory() {
     String module = "small";         // module (=file) on python.path
     String clazz = "implementation"; // class in the module
     PySystemState.initialize();
     PyObject moduleObject = imp.importName(module, false);
     if (moduleObject != null) {
       _classObject = moduleObject.__getattr__(clazz);
       // AttributeError if not found
     } else {
       throw Py.ImportError("unable to import " + module);
     }
   }

   public MyInterface getInstance() {
     return
      (MyInterface)
        _classObject.__call__().__tojava__(MyInterface.class);
   }
 }

Use it as follows:

 package test;

 public class MyInterfaceTest {
   public static void main(String args[]) {
     String start = "";
     if (args.length > 0) start = args[0];
     MyInterfaceFactory factory = new MyInterfaceFactory();
     MyInterface myInterface = factory.getInstance();
     Number result = myInterface.getNumber(start);
     System.out.println("result = " + result);
   }
 }

Finally, calling the test program:

 java test.MyInterfaceTest hey
 result = 3

> i guess the end result would be like using the jython interpreter,
> but
> without the interpretation overhead.

In my example, the file is interpreted only once, but you can create
any number of instances of MyInterface.

Best wishes,
Oti.

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