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

Question

How would I get the length of an ArrayList using a JSF EL expression?

#{MyBean.somelist.length}

does not work.

Solution 1

Yes, since some genius in the Java API creation committee decided that, even though certain classes have size() members or length attributes, they won't implement getSize() or getLength() which JSF and most other standards require, you can't do what you want.

There's a couple ways to do this.

One: add a function to your Bean that returns the length:

In class MyBean:
public int getSomelistLength() { return this.somelist.length; }

In your JSF page:
#{MyBean.somelistLength}

Two: If you're using Facelets (Oh, God, why aren't you using Facelets!), you can add the fn namespace and use the length function

In JSF page:
#{ fn:length(MyBean.somelist) }

Solution 2

You mean size() don't you?

#{MyBean.somelist.size()}

works for me (using JBoss Seam which has the Jboss EL extensions)

Solution 3

Note: This solution is better for older versions of JSTL. For versions greater then 1.1 I recommend using fn:length(MyBean.somelist) as suggested by Bill James.

---

This article has some more detailed information, including another possible solution;

The problem is that we are trying to invoke the list's size method (which is a valid LinkedList method), but it's not a JavaBeans-compliant getter method, so the expression list.size-1 cannot be evaluated.

There are two ways to address this dilemma. First, you can use the RT Core library, like this:

<c_rt:out value='<%= list[list.size()-1] %>'/>

Second, if you want to avoid Java code in your JSP pages, you can implement a simple wrapper class that contains a list and provides access to the list's size property with a JavaBeans-compliant getter method. That bean is listed in Listing 2.25.

The problem with c_rt method is that you need to get the variable from request manually, because it doesn't recognize it otherwise. At this point you are putting in a lot of code for what should be built in functionality. This is a GIANT flaw in the EL.

I ended up using the "wrapper" method, here is the class for it;

public class CollectionWrapper {

    Collection collection;

    public CollectionWrapper(Collection collection) {
        this.collection = collection;
    }

    public Collection getCollection() {
        return collection;
    }

    public int getSize() {
        return collection.size();
    }
}

A third option that no one has mentioned yet is to put your list size into the model (assuming you are using MVC) as a separate attribute. So in your model you would have "someList" and then "someListSize". That may be simplest way to solve this issue.

Solution 4

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

<h:outputText value="Table Size = #{fn:length(SystemBean.list)}"/>

On screen it displays the Table size

Example: Table Size = 5

Solution 5

After 7 years... the facelets solution still works fine for me as a jsf user

include the namespace as xmlns:fn="http://java.sun.com/jsp/jstl/functions"

and use the EL as #{fn:length(myBean.someList)} for example if using in jsf ui:fragment below example works fine

<ui:fragment rendered="#{fn:length(myBean.someList) gt 0}">
    <!-- Do something here-->
</ui:fragment>

View more solutions

Comments

[James McMahon]

Maybe the newer specifications of the EL support the size method? Can anyone confirm or deny this?

[McDowell]

@nemo - this is being addressed in a JSR245 maintenance release: blogs.sun.com/kchung/entry/jsr_245_mr_part_i (In terms of JEE specs, that'll be JEE6)

[James McMahon]

@McDowell, Thanks for the info, I'm really surprised it took them this long to get around to fixing the issue.

[Hosam Aly]

Thank you. It worked for me too. +1. But until JEE 6 is widely supported, I'll probably stick with the "more standard" JSTL function.

[Hosam Aly]

BTW, it probably works in JBoss to just say #{MyBean.somelist.size} (without the parenthesis at the end).

[Damo]

With Jboss EL if you leave out the parenthesis it tries to find getSize() or isSize()

[James McMahon]

fn is probably the way to go, unfortunately it is only available in JSTL versions greater then 1.1.

[Christopher Parker]

Using fn:length worked for me with bare JSP (no JSF, Facelets; ultra legacy project being lightly updated before being phased out). The proper taglib to use: <%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn" %>

[Damien MIRAS]

For people landing here like me, still 2 year latter, considere you may add the following namespace to your facelet: xmlns:fn="http://java.sun.com/jsp/jstl/functions"

[baybora.oren]

also stackoverflow.com/questions/1332169/…

[JackDev]

Yes this I find is the simplest way of doing it. I'm using websphere6 with JSP (legacy system). used the same tablib and then use the 'dollar sign' as opposed to 'hash' because hash didn't work. ie: {fn:length(SystemBean.list)}

[Artjom B.]

This is essentially the same answer as Damo's.

[Andrew Barber]

As @ArtjomB. sugggests, it's not generally good here to post what amounts to the same answer as someone else already posted. In this case, almost six years ago.

[Antares42]

We're on JEE 6, and while size works fine for e.g. ArrayList etc., neither size nor length are defined for Object[], so I find myself still using fn:length(...)

[Marco Sulla]

Eclipse complains: "Syntax error in EL"... but it works :D