[Annotation] @URL(protocol=, host=, port=, regexp=, flags=) [Supported data types] CharSequence [Hibernate metadata impact] None [Use] 
Checks if the annotated character sequence is a valid URL according to RFC2396. If any of the optional parameters protocol, host or port are specified, the corresponding URL fragments must match the specified values. The optional parameters regexp and flags allow to specify an additional regular expression (including regular expression flags) which the URL must match. Per default this constraint used the java.net.URL constructor to verify whether a given string represents a valid URL. A regular expression based version is also available - RegexpURLValidator - which can be configured via XML (see Section 7.2, “Mapping constraints via constraint-mappings”) or a ConstraintDefinitionContributor (see Section 11.12.2, “Constraint definitions via ConstraintDefinitionContributor”).