I would suggest using the trim function followed by a regex replacement that matches instances of the space character i.e. /(\s+)/ and replaces it with a single space

If going back to basics I would suggest using the trim() function followed by a regex replacement using replaceAll() that matches instances of the space characters i.e. (\\s+) and replaces them with a single space.

Example:

String str = ' how is   the weather today ';

str = str.trim();

str = str.replaceAll('(\\s+)', ' ');

return str;