How to add days, months or years to a Primefaces calendar input

Question

i have the following code in an .xhtml file

<!-- /row -->
    <div class="row" id="penaltyStartingDate" style="margin-top: 15px">
        <div class="span8">
            <div class="control-group">
                <label class="hcg-control-label span5">Ημερομηνία Έναρξης Ισχύος Ποινής</label>
                <div class="controls span7">
                    <p:calendar id="penaltyStartingDate" styleClass="hcg-full-width cursor-pointer" pattern="dd/MM/yyyy"
                                value="#{penaltiesView.penalty.penaltyStartingDate}" />
                    <i class="fa fa-calendar hcg-input-icon"></i>
                </div>
            </div>
        </div>
        <!-- /span -->
    </div>
    <!-- /row -->
    <div id="forfeitureDurationContainer" class="row" style="margin-top: 15px">
        <div class="span8">
            <div class="control-group">
                <label class="hcg-control-label span5">Χρόνος Στέρησης</label>
                <div class="controls span7">
                    <p:inputText id="ForfeitureDurationValue" styleClass="hcg-full-width" value="#{penaltiesView.penalty.forfeitureDurationValue}" disabled="#{!penaltiesView.canEdit()}" style="width:30%" required="false" requiredMessage="Ο χρόνος στέρησης είναι υποχρεωτικός." />
                    <p:selectOneMenu id="ForfeitureDurationType" value="#{penaltiesView.penalty.forfeitureDurationType}" disabled="#{!penaltiesView.canEdit()}" styleClass="margin-bottom-10" style="width:70%">
                        <f:selectItem itemLabel="Μήνες" itemValue="Months" />
                        <f:selectItem itemLabel="Ημέρες" itemValue="Days" />
                        <f:selectItem itemLabel="Χρόνια" itemValue="Years" />
                    </p:selectOneMenu>
                </div>
            </div>
        </div>
        <!-- /span -->
    </div>
    <!-- /row -->
    <div class="row" id="penaltyStopDate" style="margin-top: 15px">
        <div class="span8">
            <div class="control-group">
                <label class="hcg-control-label span5">Ημερομηνία Παύσης Ισχύος Ποινής</label>
                <div class="controls span7">
                    <p:calendar id="penaltyStopDate" styleClass="hcg-full-width cursor-pointer" pattern="dd/MM/yyyy" disabled="true"
                                value="#{penaltiesView.penalty.penaltyStopDate}" />
                    <i class="fa fa-calendar hcg-input-icon"></i>
                </div>
            </div>
        </div>
        <!-- /span -->
    </div>

And this is what it generates in the webpage screenshot

The first field is a primefaces calendar. The next one is a field where you put a number and from what you choose in the dropdown menu (which includes days, months, years), a calculated date must appear in the final field which i have disabled. So for example, if I add 01/06/2020 and then type 2 and choose the "days(Ημέρες)" option, in the final field must appear the date 03/06/2020.

Can you help me with this one? I would really appreciate it.

Answer 1

you can achieve it with Calendar. Add ajax in selectOneMenu:

<p:selectOneMenu id="ForfeitureDurationType" value="#{penaltiesView.penalty.forfeitureDurationType}" 
                 disabled="#{!penaltiesView.canEdit()}" styleClass="margin-bottom-10" style="width:70%">
                        <p:ajax event="change" listener="#{penaltiesView.calculatePenalty()}"
process="penaltyStartingDate,ForfeitureDurationValue,ForfeitureDurationType"/>
                        <f:selectItem itemLabel="Μήνες" itemValue="Months" />
                        <f:selectItem itemLabel="Ημέρες" itemValue="Days" />
                        <f:selectItem itemLabel="Χρόνια" itemValue="Years" />
                    </p:selectOneMenu>

Then in penaltiesView:

public void calculatePenalty() {
    Calendar c = Calendar.getInstance();
    c.setTime(penalty.penaltyStartingDate);
    if (penalty.forfeitureDurationType.equals("Months") {
        c.add(Calendar.MONTH, penalty.forfeitureDurationValue);
        penalty.penaltyStopDate = c.getTime();
    } else if (penalty.forfeitureDurationType.equals("Days") {
        c.add(Calendar.DAY_OF_MONTH, penalty.forfeitureDurationValue);
        penalty.penaltyStopDate = c.getTime();
    } else {
        c.add(Calendar.YEAR, penalty.forfeitureDurationValue);
        penalty.penaltyStopDate = c.getTime();
    }
    PrimeFaces.current().ajax().update("penaltyStopDate");
}