org.hibernate.QueryException: could not resolve property: filename
Solution 1:
Hibernate queries are case sensitive with property names (because they end up relying on getter/setter methods on the @Entity).
Make sure you refer to the property as fileName in the Criteria query, not filename.
Specifically, Hibernate will call the getter method of the filename property when executing that Criteria query, so it will look for a method called getFilename(). But the property is called FileName and the getter getFileName().
So, change the projection like so:
criteria.setProjection(Projections.property("fileName"));