No manejo Java pero... ¿has probado a usar la función Arrays.deepToString()?:
¡Saludos!
Cita de: http://docs.oracle.com/javase/6/docs/api/java/util/Arrays.html#deepToStringdeepToString Returns a string representation of the "deep contents" of the specified array. If the array contains other arrays as elements, the string representation contains their contents and so on.
This method is designed for converting multidimensional arrays to strings.
¡Saludos!