* @return The generated validity object or <code>null</code> if the
* component is currently not cacheable.
*/
public SourceValidity getValidity() {
if (this.lastModified > 0) {
return new TimeStampValidity(this.lastModified);
} else {
if (this.defaultCache) {
return NOPValidity.SHARED_INSTANCE;
} else {
return null;