PrimeFaces dataTable: how to catch rows-per-page event?

I cretated a PrimeFaces dataTable:

<p:dataTable id="locationTable" value="#{bean.object}" var="item"
  paginator="true"
  rows="10" 
  paginatorTemplate="{FirstPageLink} {PreviousPageLink} {PageLinks} {NextPageLink}{LastPageLink} {RowsPerPageDropdown}" 
  rowsPerPageTemplate="5,10,15,20,30,50,100">
  ...
</p:dataTable>

I'd like to save the dropdown box value for rows-per-page. When the user changes the value, how would I catch the event? So I can read and save one of the "5,10,15,20,30,50,100" values in order for this to apear automatically next time the user comes back to this page. Currently, it is not saved, so every time the page is (re)loaded, it goes back to default value of "10".

You can do that like this:

The View

<h:form id="mainForm">

    <p:dataTable id="locationTable" value="#{datatableBean.list}" var="item"
                 paginator="true" widgetVar="dtVar"
                 rows="#{datatableBean.rows}" 
                 paginatorTemplate="{CurrentPageReport}  {FirstPageLink} {PreviousPageLink} {PageLinks} {NextPageLink} {LastPageLink} {RowsPerPageDropdown}"
                 rowsPerPageTemplate="1,2,3,4,5,6">
        <p:column>
            #{item.name}
        </p:column>
    </p:dataTable>

    <p:remoteCommand name="persistRows" action="#{datatableBean.saveRows}" process="@this" 
                     update="rows" global="false" />

    <h:outputText id="rows" value="#{datatableBean.rows}" />

    <script>
        jQuery(document).ready(function() {
            dtVar.paginator.rppSelect.change(function() {
                persistRows([{name: 'rows', value: this.value}]);
            });
        });
    </script>
</h:form>

The Bean

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import javax.annotation.PostConstruct;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.SessionScoped;
import javax.faces.context.FacesContext;

@ManagedBean
@SessionScoped
public class DatatableBean implements Serializable {

    private int rows;

    private List<SimpleBean> list;

    @PostConstruct
    public void setup() {
        //default rows value
        rows = 2;

        list = new ArrayList<SimpleBean>();
        //ID and Name
        list.add(new SimpleBean(11, "A"));
        list.add(new SimpleBean(22, "B"));
        list.add(new SimpleBean(33, "C"));
    }

    public void saveRows(){
        FacesContext context = FacesContext.getCurrentInstance();
        Map map = context.getExternalContext().getRequestParameterMap();
        String rowsStr = (String) map.get("rows");
        rows = Integer.parseInt(rowsStr);
    }

    public int getRows() {
        return rows;
    }

    public void setRows(int rows) {
        this.rows = rows;
    }

    public List<SimpleBean> getList() {
        return list;
    }

    public void setList(List<SimpleBean> list) {
        this.list = list;
    }

}

The strategy here is to extend the onchange event associated with the html select tags rendered by the paginator. To facilitate that task, I've set the wigetVar in the datatable (dtVar) knowing that it's clientside api gives us both selects through dtVar.paginator.rppSelect.

Now, to be able to send the value on those selects to the managed bean, we can use a remoteCommand. Using the remoteCommand component we can send javascript parameters to a managedbean. I've named the remoteCommand as persistRows and by calling it I've specified the extra parameters using the pattern required by the component: [{name: 'rows', value: this.value}] ([{name: 'nameOfTheVariable', value: 'valueOfTheVariable'}]).

Now you can do whatever you want to do with that rows attribute.

I posted this solution to another question, and I'm sharing it because I hope someone might find it simpler to implement than Daniel's (which still taught me a lot about JQuery!)

My solution is using Primefaces 5.2.x.

I found a pretty easy way to implement this, one of the problems I had was that when the onPaginate() method was called, it didn't have the newest selected value.

So here's what I did to make sure you always had the latest value and could save/load it to the database or a cookie or something (we save to a cookie).

<p:dataTable
        .....
        paginator="true"
        paginatorPosition="bottom"
        paginatorTemplate="{CurrentPageReport} {FirstPageLink} {PreviousPageLink} {PageLinks} {NextPageLink} {LastPageLink} {RowsPerPageDropdown}"
        currentPageReportTemplate="Total records: {totalRecords}, showing page {currentPage} of {totalPages}"
        rowsPerPageTemplate="25,50,100"
        rows="#{controller.rowsPerPage}"
        .....
    >
        .....
        <p:ajax event="page" oncomplete="rowsPerPageUpdate()" />
        .....
</p:dataTable>
<p:remoteCommand name="rowsPerPageUpdate" actionListener="#{controller.onPaginate}" />

and then our controller looks like this:

@Dependent
@Named
public class TableController implements Serializable {
    private String rowsPerPage = "25"; //default value
    .....
    public void onPaginate() {
        //save to the cookie
    }
    .....
}

Basically the magic happens in the remoteCommand, which will fire after the ajax event to insure that controller.rowsPerPage has been properly updated.

I've searched for a solution too and after reading this thread I've found out that there's a new Primefaces feature which allows you to save the state of the datatable.

So for Primefaces v6.0.10+ you can simply add multiViewState="true".

Note that this will also save filter, sorting, current page and selection beside rows per page.

Here's the link to the official demo of this feature: https://www.primefaces.org/showcase/ui/data/datatable/tableState.xhtml