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.

JAXB and Java IO (Files, Streams, Readers, and Writers)

JAXB supports many different XML sources and targets.  In this post I'll give an overview of how JAXB can be used with those found in the java.io package: File, InputStream, OutputStream, Reader, Writer and their subclasses.

JAXB and Marshal/Unmarshal Schema Validation

In a previous post I described how to validate an object model (mapped with JAXB annotations) against an XML schema using the javax.xml.validation APIs.  In this post I'll describe how to leverage those APIs during unmarshal and marshal operations.