JSTL - Using forEach to iterate over a user-defined class

Question

What methods do I need to add to a custom Java class so that I can iterate over the items in one of its members? I couldn't find any specifications about how the JSTL forEach tag actually works so I'm not sure how to implement this.

For example, if I made a generic "ProjectSet" class and I woud like to use the following markup in the JSP view:

<c:forEach items="${projectset}" var="project">
...
</c:forEach>

Basic class file:

public class ProjectSet {
    private ArrayList<Project> projects;
    public ProjectSet() {
        this.projects = new ArrayList<Project>();
    }
    // .. iteration methods ??
}

Is there any interface that I must implement like PHP's ArrayAccess or Iterator in order for this to work?

Edit: Without directly accessing the ArrayList itself, because I will likely be using some sort of Set class using generics, and the JSP view shouldn't have to know about the inner workings of the class.

Dominik · Accepted Answer · 2015-11-22T17:41:14.787

4

The Iterable interface provides this functionality:

public class ProjectSet implements Iterable<Project> {
    private ArrayList<Project> projects;
    public ProjectSet() {
        this.projects = new ArrayList<Project>();
    }

    // .. iteration methods ??
   @Override
   public Iterator<Project> iterator() {
       return projects.iterator();
   }
}

You can exchange the iterator logic as you need.

edited Nov 22 '15 at 17:41

answered Jun 05 '10 at 00:23

Dominik

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9

Caveat to that is that JSTL forEach does not support iterable (extremely annoying) as forEach type. So you need to do ${projectSet.iterator()} – Adam Gent Feb 13 '11 at 15:16
2

Actually .iterator() will only work on the latest Servlet Container (and even the latest JSTL still does not support iterable). You will need to make a getter for the iterator ( getIterator() ). – Adam Gent Feb 14 '11 at 00:29

score 0 · Answer 2 · answered Jun 05 '10 at 00:22

0

Yes, you should implement java.util.Iterable

answered Jun 05 '10 at 00:22

Behrang

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score 0 · Answer 3 · answered Oct 19 '18 at 16:57

Unfortunately, the forEach tag does not support Iterable as the items source. It does support:

Arrays
Collection
Iterator
Enumeration
Map
Comma-separated list of values given in a String

(relevant source code: ForEachSupport)

Of these, it's probably best to use an Iterator as the forEach source when you wish to fetch items from your own class.

JSTL - Using forEach to iterate over a user-defined class

3 Answers3

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