How do I check that a Java String is not all whitespaces?

Shortest solution I can think of:

if (string.trim().length() > 0) ...

This only checks for (non) white space. If you want to check for particular character classes, you need to use the mighty match() with a regexp such as:

if (string.matches(".*\\w.*")) ...

...which checks for at least one (ASCII) alphanumeric character.

I would use the Apache Commons Lang library. It has a class called StringUtils that is useful for all sorts of String operations. For checking if a String is not all whitespaces, you can use the following:

StringUtils.isBlank(<your string>)

Here is the reference: StringUtils.isBlank

Slightly shorter than what was mentioned by Carl Smotricz:

!string.trim().isEmpty();