Get the value of t:inputCalendar if readonly is true

<t:inputCalendar id="cal" value="#{backingBean.date1}"
        renderAsPopup="true"
        popupDateFormat="MM/dd/yyyy"
        popupTodayDateFormat="dd-MMM-yyyy"
        popupWeekString="Week"
        popupTodayString="The date today is :"
        renderPopupButtonAsImage="true"
        helpText="MM/DD/YYYY"
        readonly="true"/>

To get the value in the backing bean just add the below code.
When readonly attribute is true, the component cannot be edited by the user.(ie the text box in the calendar cannot be edited.)

bodyId:id of body tag
formId:id of form tag
String dateString = (String) getExternalContext().getRequestParameterMap().get("bodyId:formId:date1");

SimpleDateFormat dateFormat = new SimpleDateFormat("MM/dd/yyyy",
                 getCurrentLocale());