To refer to external Java helper class methods (like StringUtils from Apache commons library) in the Validation field on the Configurable Validation page, simply use method invocation by providing required parameters.
For example, in Performance Budgeting, to check if String field is populated or blank in validation:
StringUtils.isBlank( code )
or
StringUtils.isBlank( name )
For example, in Financial, HRM, VSS, and Administration, to check if String field is populated or blank in validation:
StringUtils.isBlank( this.getFUND_CD() )
or
StringUtils.isBlank( FUND_NM )