Could some resources be listed in relation to the creation and management of simplistic, efficient 2D game levels, that are available for use with Java?
Have a look at Tiled or OGMO Editor. These editors allow you to create your levels and can also write the level-data to XML. Parsing the XML data in Java should be rather simple. Alternatively you could have a look at the AndEngine which comes with a parser for the TMX format (TMX is an XML format written by Tiled).
try to look at www.processing.org it's a simple and quite power system for making 2d in java