Mixing Nesting and References with JAXB's XmlAdapter

Recently I came across a question on Stack Overflow asking if JAXB could marshal the first occurrence of an object as containment and all subsequent occurrences as a reference.  Below is an expanded version of my answer (up votes appreciated) demonstrating how this can be achieved by leveraging JAXB's XmlAdapter.

Mapping Objects to Multiple XML Schemas - Weather Example

I have written previous posts on EclipseLink JAXB (MOXy)'s @XmlPath and external binding file extensions.  In this post I will demonstrate how powerful these extensions are by mapping a single object model to two different XML schemas.  To make the example more "real", the XML data will come from two different services that provide weather information:  Google and Yahoo.