This is a simple and some what dumb library to facliltate conversion between custom Java types and Erlang.

CoversionManager cm = new ConversionManager();

// loads basic convertors for integers, booleans, 
// strings and the like
cm.registerBasic(); 

ArrayList arr = new ArrayList();
arr.add("hello");
arr.add(10);

OtpErlangList list = cm.convert(arr);
// if you send this list over to Erlang, you'll get
// ["hello", 10] 

A basic usage would be something like this:

ConversionManager cm = new ConversionManager();
cm.registerBasic();

cm.register(
    new MyCustomConverter1(),
    new MyCustomConverter2(),
    new MyCustomConverter3()
);

OtpNode self = new OtpNode("node@localhost");
OtpMbox mbox = self.createMbox("mbox");

while(true) {
    Object o = o = mbox.receive();

    Object result = do_something_horrible(o);
    OtpErlangObject out = cm.convert(result);

    mbox.send(from, out);
}

See implementation of ArrayListConverter to see how to create a fairly complex converter.
See implementation of ConversionManager.registerBasic to see how to register your own converters.