An implementation of a Jython FastGetter that doesn't work for some reason.

FastGetter.java

package jesreflect;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import org.python.core.Py;
import org.python.core.PyObject;

/**
 * An optimized getter that's designed to invoke a Java class's
 * getSomething method, with no arguments, and wrap the return value.
 */
class FastGetter extends PyObject {
    private Class<?> owningClass;
    private Method method;
    private String messagePrefix;

    public FastGetter (String className, String methodName)
            throws ClassNotFoundException, NoSuchMethodException {
        this(className, methodName, "");
    }

    public FastGetter (String className, String methodName, String messagePrefix)
            throws ClassNotFoundException, NoSuchMethodException {
        owningClass = Class.forName(className);
        // We're getting the method with 0 arguments.
        method = owningClass.getMethod(methodName);
        messagePrefix = messagePrefix;
    }


    // Python method overrides

    public boolean isCallable () {
        return true;
    }

    @Override
    public PyObject __call__ (PyObject[] args, String[] keywords) {
        return FastGetter___call__(args, keywords);
    }

    public PyObject __call__ (PyObject arg) {
        return invoke(arg);
    }


    // Actually calling

    public PyObject FastGetter___call__ (PyObject[] args, String[] keywords) {
        // Check that we have the right arguments.
        if (args.length != 1 && keywords.length != 0) {
            throw Py.TypeError(messagePrefix + "Can only be called with one argument");
        }

        return invoke(args[0]);
    }

    public PyObject invoke (PyObject pyOwner) {
        // Cast the argument they passed to the owning type.
        Object owner = pyOwner.__tojava__(owningClass);
        if (owner == Py.NoConversion) {
            throw Py.TypeError(messagePrefix + "Input is not a " +
                               owningClass.getSimpleName());
        }

        // Invoke it!
        Object value = null;
        try {
            value = method.invoke(owner);
        } catch (InvocationTargetException exc) {
            throw Py.JavaError(exc.getCause());
        } catch (IllegalAccessException exc) {
            throw Py.JavaError(exc);
        }

        return Py.java2py(value);
    }
}

what-happens-when-i-try-to-use-it

Jython 2.5.3 (2.5:c56500f08d34+, Aug 13 2012, 14:48:36) 
[OpenJDK 64-Bit Server VM (Oracle Corporation)] on java1.8.0_05
Type "help", "copyright", "credits" or "license" for more information.
>>> from jesreflect import FastGetter
>>> getter = FastGetter('java.lang.String', 'length')
>>> dir(getter)
['__class__', '__delattr__', '__doc__', '__getattribute__', '__hash__', '__init__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__str__']
>>> getter("Hi!")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'jesreflect.FastGetter' object is not callable
>>> getter
#
# A fatal error has been detected by the Java Runtime Environment:
#
#  SIGSEGV (0xb) at pc=0x00007f1509409f40, pid=12980, tid=139728348034816
#
# JRE version: OpenJDK Runtime Environment (8.0_05-b13) (build 1.8.0_05-b13)
# Java VM: OpenJDK 64-Bit Server VM (25.5-b02 mixed mode linux-amd64 compressed oops)
# Problematic frame:
# V  [libjvm.so+0x79cf40]  JVM_FindSignal+0x161850
#
# Failed to write core dump. Core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again
#
# An error report file with more information is saved as:
# /home/matthew/groups/gatech/jes/hs_err_pid12980.log
Could not load hsdis-amd64.so; library not loadable; PrintAssembly is disabled
#
# If you would like to submit a bug report, please visit:
#   http://bugreport.sun.com/bugreport/crash.jsp
#