So, I figured this out by looking and debugging around in the JAXB
source code.
Here's what happened:
I had a class that looked like this:
@XmlType(name = "")
public class Param {
@XmlValue() private String value;
@XmlAttribute() private String name;
public String getValue() {...}
public void setValue(String value) {...}
public String getName() {...}
public String setName(String name) {...}
}
The problem occurred because I had a value/attribute and properties in
the same class, without using @XmlTransient on the properties or
@XmlAccessorType(AccessType.FIELD) on the class. JAXB got peeved because
I had both field definitions and properties and you can't have both.
These UnsupportedOperationException throws should really be updated to
have better error messages since this is a likely problem when building
your own JAXB beans.