The JDK's String.trim() method is pretty naive, and only removes ascii control characters.
Apache Commons' StringUtils.strip() is slightly better, but uses the JDK's Character.isWhitespace(), which doesn't recognize non-breaking space as whitespace.
So what would be the most complete, Unicode-compatible, safe and proper way to trim a string in Java?
And incidentally, is there a better library than commons-lang that I should be using for this sort of stuff?
This handles Unicode characters and doesn't require extra libraries:
String trimmed = original.replaceAll ("^\\p{IsWhite_Space}+|\\p{IsWhite_Space}+$", "");
A slight snag is that there are some related whitespace characters without Unicode character property "WSpace=Y" which are listed in Wikipedia. These probably won't cause a problem, but you can easy add them to the character class too.
Using almson-regex the regex will look like:
String trimmed = original.replaceAll (either (START_BOUNDARY + oneOrMore (WHITESPACE), oneOrMore (WHITESPACE) + END BOUNDARY), "");
and include the more relevant of the non-Unicode whitespace.