The DefaultFormatter is the class that is used to convert an Entry<Key,Value> to the line of text displayed in the shell. Most notably, it encodes non-printable ASCII data as hex.
For users who want to implement their own Formatter, they do not have access to the same formatting methods that the DefaultFormatter uses because of the visibility modifiers on the methods. These methods should be available for use by other classes. Letting classes extend the DefaultFormatter would be even better.
Additionally, in the DefaultFormatter, in the method public static String formatEntry(Entry<Key,Value>, DateFormat), a StringBuilder is used to reduce the number of intermediate String objects that are created for each concatenation; however, the methods to get each component of the Key will create a new Text object each time.
Method invocations like
Should be replaced with:
Text buffer = new Text();
Where a single Text object is reused for the entire method.