In addition to MongoDB's built in Java driver, Jongo, Morphia and Spring Data are all popular third-party solutions that make it easier to view and manipulate data in MongoDB. InsaneProgramming blogger Lieven Doclo offers a to-the-point MongoDB Java comparison using a REST-based service as a use case. From his notes:
MongoDB Java driver
The most low-level approach for accessing a MongoDB database from the JVM.
The least user friendly but possibly the most versatile of the solutions; "there’s nothing you can’t do with the Java driver."