com.mastfrog:simplevalidation (maven):  This is a simple library for quickly adding validation code to Swing user-interfaces. It handles validating user input when the user changes a component's value, showing error messages and decorating components to indicate which component is the source of the problem. It contains a large number of built-in validators to handle most common situations, such as validating numbers, email addresses, urls and so forth. 
Keywords: java|java-net|swing-api|validation