I googled for solutions or examples, but all I can find is, that JPA does not support mapping of custom data types. Is it still in JPA 2.0?
Yes. So you'll have to rely on specific extensions. For Hibernate, the Hibernate Spatial project provides ready to use spatial dialects and custom types:
Hibernate Spatial is a generic
extension to Hibernate for handling
geographic data. Hibernate Spatial is
open source and licensed, like
Hibernate, under the LGPL license.
Hibernate Spatial allows you to deal
with geographic data in a standardized
way. It abstracts away from the
specific way your database supports
geographic data, and provides a
standardized, cross-database interface
to geographic data storage and query
functions.
Hibernate Spatial supports most of the
functions of the OGC Simple Feature
Specification. Supported databases
are: Oracle 10g/11g,
Postgresql/Postgis, Microsoft SQL
Server and MySQL.