ui/src/main/java/thredds/ui/datatype/prefs/DateField.java
@Override
  protected boolean _validate(StringBuffer buff) {
    try {
      new DateType(tf.getText(), null, null);
      return true;
    } catch (java.text.ParseException e) {
      if (null != buff) buff.append(name).append(": ").append(e.getMessage());
      return false;
    }
  }
@Override
  protected boolean _validate(StringBuffer buff) {
    try {
      new DateType(tf.getText(), null, null);
      return true;
    } catch (java.text.ParseException e) {
      if (null != buff) buff.append(name).append(": ").append(e.getMessage());
      return false;
    }
  }
See if edit value is valid, put error message in buff.