If you like to use the Pretty Print feature, you must configure your Gson instance using the GsonBuilder. The JsonFormatter is not exposed through our public API, so the client is unable to configure the default print settings/margins for the JSON output. For now, we only provide a default JsonPrintFormatter that has default line length of 80 character, 2 character indentation, and 4 character right margin.
The following is an example shows how to configure a Gson instance to use the default JsonPrintFormatter instead of the JsonCompactFormatter:
Gson gson = new GsonBuilder().setPrettyPrinting().create();
String jsonOutput = gson.toJson(someObject);