JOT Servlets - Programmers Guide

Programmers Guide > JOT Iterators

JOT Iterators

JotTemplateIterators render dynamic tables and lists using Java Collections and JDBC ResultSets. JOT Iterators are easily adapted for use with any other group of objects (see JotIteratorSource).

The JOT.Repeat template token starts a loop that repeats a section of a JOT Template up to a matching JOT.End token. The looping continues while the argument to JOT.Repeat is true. This boolean argument is typically a JOT.Next token that refers to a JotTemplateIterator. In the following example, Items is a name for a JotTemplateIterator. Items.ProductName and Items.ProductPrice take on values from the current element in the iteration loop.

    JOT.Repeat(JOT.Items.Next)
        <tr>
            <td>JOT.Items.ProductName</td>
            <td>JOT.Items.ProductPrice</td>
        </tr>
    JOT.End

A useful design idiom for JOT Iterators is an inner class that extends JotTemplateIteratorBean, JotCollectionIteratorBean, or JotMapIteratorBean. The next code fragment continues the example with an inner Items class that enumerates the elements of a Vector of Products. Each pass of the JOT.Repeat(JOT.Items.Next) loop advances the iterator to the next Product object in the Enumeration which is returned by getElement().

    // Fragment of a JotServletPropertyBean...
    {
        Vector products = new Vector();
        products.addElement(new Product("Basic Widget",199.99));
        products.addElement(new Product("Super Widget",123.45));
        products.addElement(new Product("Broken Widget",0));
    }

    public void prepareJotBean()
        throws JotException
    {
         super.prepareJotBean();
         addJotBeanProperty("Items", new Items()); // create property
    }

    // Inner class
    public class Items
        extends JotTemplateIteratorBean
    {
        Items()
        {
            super(new JotEnumIterator(products.elements()));
        }
        public String getProductName()
        {
            return ((Product)getElement()).productName;
        } 
        public String getProductPrice()
        {
            return fmt.format(((Product)getElement()).price);
        } 
    }

The properties of the current element in an iteration are automatic properties of the JotTemplateIterator. The previous example can be refactored to eliminate the Items subclass if getProductName() and getProductPrice() are methods of the Product class, as shown here with a JotCollectionIteratorBean.

    // Fragment of a JotServletPropertyBean...

    public void prepareJotBean()
        throws JotException
    {
         super.prepareJotBean();
         // create "Items" JOT Iterator property
         addJotBeanProperty("Items", new JotCollectionIteratorBean(products));
    }

The JotTemplateIterator element property references the current object in an iteration. The position property renders the ordinal position (element count) of the current object. In this example the Product object is passed to the getSalesPrice() method:

    JOT.Repeat(JOT.Items.Next)
        <tr>
            <td>JOT.Items.Position</td>
            <td>JOT.Items.ProductName</td>
            <td>JOT.Items.ProductPrice</td>
            <td>JOT.SalesPrice(JOT.Items.Element)</td>
        </tr>
    JOT.End

The JOT Servlets documentation provides further JOT Iterator examples showing how to limit the number of iterations and how to use JOT Iterators with JDBC ResultSets.