You don't need an outside library.
Use the built in pretty printer in Sling's JSONObject: http://sling.apache.org/apidocs/sling5/org/apache/sling/commons/json/JSONObject.html#toString(int)
public java.lang.String toString(int indentFactor)
throws JSONException
Make a prettyprinted JSON text of this JSONObject. Warning: This method assumes that the
data structure is acyclical.
Parameters:
indentFactor - The number of spaces to add to each level
of indentation.
Returns: a printable, displayable, portable,
transmittable representation of the object, beginning with { (left
brace) and ending with } (right brace).
Throws: JSONException - If the
object contains an invalid number.
