java - REGEX.. convert X_FOO_BAR to fooBar -

I am writing a Java DAo class that reads a table's metadata and changes the column names. Based on the following rules I have a problem with REEGEX.

  - Delete the first 2 characters - With the exception of the first letter after underscores, all the letters are all letters Change in (_) symbol - Underscores   
 such ...  
  X_H -> H X_THE_FIND - & gt; The Fund Y_SCORE_CARD - & gt; Scorecard Y_PARTNER - & gt; Partner   
 (Note: The database column contains only uppercase letters and may contain one or more underscores characters, the first 2 characters will always be either X_ or Y_. Name must be at least 3 characters.)   
 
 
 It can be used in 1 line:  
  // assuming str string str = WordUtils.capitalizeFully (str.substring (2), new four [] {'_'}). Replacement ("_", "");