I hate JAXB.  I hate Jackson. I hate Hibernate.  I’m sick and tired of writing all these stupid mapping classes for JSON, XML, and ORM.  Wouldn’t it be awesome if you could evaluate JSON and XML the same way Javascript can?  You could if Java supported dynamic dispatch.  Basically the ability to dispatch method invocations and field access dynamically at runtime without compiler checking code.  Dynamic languages like Python, et. al. have always supported this type of feature, and I believe Scala does too.  IMO, it should be as simple as implementing a DynamicDispatch interface

interface DynamicDispatch {
   Object invoke(Class returnType, Type genericReturnType, String methodName, Object... args);
   Object getField(Class type, Type genericType, String fieldName);
   void setField(String filedName, Object value);

This would have a tremendous effect on productivity and maintenance as we could get rid of JSON and XML mapping. I would even say we could do some really innovative things in the ORM space as well.