How to get the length of a list in the JSF expression language?

How to get the length of a list in the JSF expression language?

In JavaServer Faces (JSF), you can use the fn:length() function from the JSTL (JavaServer Pages Standard Tag Library) to get the length of a list or collection in the expression language (EL). Here's how you can use it:

Assuming you have a list named myList in your backing bean:

import java.util.ArrayList;
import java.util.List;

@ManagedBean
@ViewScoped
public class MyBean implements Serializable {
    private List<String> myList;

    public MyBean() {
        myList = new ArrayList<>();
        myList.add("Item 1");
        myList.add("Item 2");
        myList.add("Item 3");
    }

    // Getter and setter for myList
}

You can access the length of myList in your JSF page using the fn:length() function as follows:

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions" %>

<h:outputText value="The length of myList is: #{fn:length(myBean.myList)}" />

In the code above:

  • <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %> and <%@ taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions" %> are used to import the JSTL core and functions tag libraries.

  • fn:length(myBean.myList) calculates the length of myList by invoking the fn:length() function with the EL expression myBean.myList. Replace myBean with the actual name of your managed bean.

This expression will evaluate to the length of the list and display it on your JSF page. Make sure that you have the JSTL libraries included in your project's dependencies, as JSF often relies on them for various operations.

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