http://struts.apache.org/userGuide/dev_validator.html说:
date - validates that a field can be converted to a Date. This validator uses java.text.SimpleDateFormat to parse the date and optionally either a datePattern or datePatternStrict variable can be used. If no pattern is specified the default short date format is assumed. The difference between using the datePatternStrict and datePattern variables is that datePatternStrict checks additionally that the input data is the same length as the pattern specified (so for example 1/1/2004 would fail with a pattern of MM/dd/yyyy).