Is Reflection needed to apply the correct generic adapter to my object dynamically

I am currently working on a serialization routine which uses a library of generically typed adapters. If the object being serialized is an instance of one of the specific adapters I have, then I need to call that adapter on the object prior to performing my other serialization procedures.

The following code works:

private final static String serialize(Object obj, Map<Class<?>, 
        XmlAdapter<?,?>> classToAdapterMap) throws JAXBException 
{
    Object adaptedObj = null;

    for (Class<?> clazz : classToAdapterMap.keySet()) {
        if (clazz.isInstance(obj)) {
            XmlAdapter<?,?> adapter = classToAdapterMap.get(clazz);
            Class<?>[] argTypes = new Class[] {clazz};
            try {
                Method method = adapter.getClass().getMethod("marshal", argTypes);
                adaptedObj = method.invoke(adapter, obj);
                break;
            } catch (Exception e) {
                // handle method retrieval and invocation related exceptions
            }
        }
    }

    // serialize
}

However, I had originally thought that I would be able to do this more simply, for example with code like:

/* DOES NOT WORK */
private final static String serialize(Object obj, Map<Class<?>, 
        XmlAdapter<?,?>> classToAdapterMap) throws JAXBException 
{
    Object adaptedObj = null;

    for (Class<?> clazz : classToAdapterMap.keySet()) {
        if (clazz.isInstance(obj)) {
            XmlAdapter<?,?> adapter = classToAdapterMap.get(clazz);
            adaptedObj = adapter.marshal(clazz.cast(obj));
            break;
        }
    }

    // serialize
}

Clearly the problem is that the wildcard generically typed adapter isn't guaranteed to handle an object of type clazz. However, I can't indicate that these two are the same by changing the method signature—as I might otherwise do—to private final static <T> String serialize(Object obj, Map<Class<T>, XmlAdapter<?,T>> classToAdapterMap), because the map needs to hold adapters of all different types.

What would be a better way to do this? Or should I stick with the Reflection based solution?

Thanks in advance,

-Dan