Java annotation for Null but neither Empty nor Blank

Question

Is there are any java annotation(s) that can validate like the example below?

String test;
test = null; //valid
test = ""; //invalid
test = " &         


        

Answer 1

Where is a nice javax.validation.constraints.Pattern annotation.

You can annotate the field with:

@Pattern(regexp = "^(?!\\s*$).+", message = "must not be blank")

This checks if field matches regex. The regex itself is something but not blank (see details here). It uses negative lookahead.