How to bind List values to selectManyListbox in JSF

问题

The situation: I have a JavaServer Faces page and a session-scoped managed bean that has two ArrayList<Integer> properties: one for holding a list of possible values and another for holding a list of selected values. On the JSF page there is a <h:selectManyListBox> component with these two properties bound.

The problem: after submitting the form the selected values will be converted to string (the property of type ArrayList actually holds a couple of strings!); however, when I use a converter, I get an error message like this:

Validation Error: Value is not valid

The question: How can I bind an ArrayList<Integer> property to the <h:selectManyListBox> component properly?

Thank you for your kind helping me.

The concrete codes

The JSF page:

<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:ui="http://java.sun.com/jsf/facelets"
      xmlns:h="http://java.sun.com/jsf/html"
      xmlns:f="http://java.sun.com/jsf/core">
    <h:body>
        <h:form>
            <h:selectManyListbox value="#{testBean.selection}">
                <f:selectItems value="#{testBean.list}"></f:selectItems>
            </h:selectManyListbox>
            <h:commandButton action="#{testBean.go}" value="go" />
            <ui:repeat value="#{testBean.selection}" var="i">
                #{i}: #{i.getClass()}
            </ui:repeat>
        </h:form>
    </h:body>
</html>

And the managed bean:

import java.io.Serializable;
import java.util.ArrayList;

@javax.faces.bean.ManagedBean
@javax.enterprise.context.SessionScoped
public class TestBean implements Serializable
{
    private ArrayList<Integer> selection;
    private ArrayList<Integer> list;

    public ArrayList<Integer> getList()
    {
        if(list == null || list.isEmpty())
        {
            list = new ArrayList<Integer>();
            list.add(1);
            list.add(2);
            list.add(3);
        }
        return list;
    }

    public void setList(ArrayList<Integer> list)
    {
        this.list = list;
    }

    public ArrayList<Integer> getSelection()
    {
        return selection;
    }

    public void setSelection(ArrayList<Integer> selection)
    {
        this.selection = selection;
    }

    public String go()
    {
            // This throws an exception: java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer
            /*for (Integer i : selection)
            {
                System.out.println(i);
            }*/
        return null;
    }
}

回答1:

The generic type information of List<Integer> is lost during runtime and therefore JSF/EL who sees only List is not able to identify that the generic type is Integer and assumes it to be default String (as that's the default type of the underlying HttpServletRequest#getParameter() call during apply request values phase).

You need either to explicitly specify a Converter, you can use JSF builtin IntegerConverter:

<h:selectManyListbox ... converter="javax.faces.Integer">

or just to use Integer[] instead, whose type information is clearly known during runtime:

private Integer[] selection;

来源：https://stackoverflow.com/questions/13865804/how-to-bind-listinteger-values-to-selectmanylistbox-in-jsf

标签

jsf-2

glassfish

managed-bean

How to bind List<Integer> values to selectManyListbox in JSF

问题

回答1: