Java – JSTL – iterating user-defined classes using foreach

See English answer > javax servlet. ServletException: javax. servlet. jsp. Jsptagexception: don't know how to iterate over supplied "items" in < foreach > 2

For example, if I create a generic "projectset" class, I want to use the following tags in the JSP view:

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

Basic class files:

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

Is there any interface I must implement, such as arrayaccess or iterator in PHP, to make it work?

Edit: there is no direct access to the ArrayList itself, because I may use a generic set class, and the JSP view should not know the internal work of the class

Solution

The Iterable interface provides this function:

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 swap iterator logic as needed