What can <f:metadata>, <f:viewParam> and <f:viewAction> be used for?

Question

Can anyone clarify how we can use in general, or a in real world example, this snippet?

<f:metadata>
    <f:viewParam id="id" value="#{bean.id}" />
    <f:viewAction action="#{bean.init}" />
</f:metadata>

Answer 1

Send params from View to an other View, from Sender View to Receiver View use viewParam and includeViewParams=true

In Sender

1. Declare params to be sent. We can send String, Object,…

Sender.xhtml

<f:metadata>
      <f:viewParam name="ID" value="#{senderMB._strID}" />
</f:metadata>

2. We’re going send param ID, it will be included with “includeViewParams=true” in return String of click button event Click button fire senderMB.clickBtnDetail(dto) with dto from senderMB._arrData

Sender.xhtml

<p:dataTable rowIndexVar="index" id="dataTale"value="#{senderMB._arrData}" var="dto">
      <p:commandButton action="#{senderMB.clickBtnDetail(dto)}" value="??" 
      ajax="false"/>
</p:dataTable>

In senderMB.clickBtnDetail(dto) we assign _strID with argument we got from button event (dto), here this is Sender_DTO and assign to senderMB._strID

Sender_MB.java
    public String clickBtnDetail(sender_DTO sender_dto) {
        this._strID = sender_dto.getStrID();
        return "Receiver?faces-redirect=true&includeViewParams=true";
    }

The link when clicked will become http://localhost:8080/my_project/view/Receiver.xhtml?*ID=12345*

In Recever

1. Get viewParam Receiver.xhtml In Receiver we declare f:viewParam to get param from get request (receive), the name of param of receiver must be the same with sender (page)

Receiver.xhtml

<f:metadata><f:viewParam name="ID" value="#{receiver_MB._strID}"/></f:metadata>

It will get param ID from sender View and assign to receiver_MB._strID

2. Use viewParam In Receiver, we want to use this param in sql query before the page render, so that we use preRenderView event. We are not going to use constructor because constructor will be invoked before viewParam is received So that we add

Receiver.xhtml

<f:event listener="#{receiver_MB.preRenderView}" type="preRenderView" />

into f:metadata tag

Receiver.xhtml

<f:metadata>
<f:viewParam name="ID" value="#{receiver_MB._strID}" />
<f:event listener="#{receiver_MB.preRenderView}"
            type="preRenderView" />
</f:metadata>

Now we want to use this param in our read database method, it is available to use

Receiver_MB.java
public void preRenderView(ComponentSystemEvent event) throws Exception {
        if (FacesContext.getCurrentInstance().isPostback()) {
            return;
        }
        readFromDatabase();
    }
private void readFromDatabase() {
//use _strID to read and set property   
}