Implementation

There is a lot of (not only java-based) implementations, many have a GUI, allowing to graphically design transformation flows.

Clover ETL

http://www.cloveretl.org - open source ETL tool including GUI

Microsoft SQL Server Integration Services

http://www.microsoft.com/sql/technologies/integration/default.mspx

Octopus Java/XML ETL Tool

http://octopus.enhydra.org/

java-etl

http://code.google.com/p/java-etl/

Kettle

http://kettle.pentaho.org/