Jakarta Commons Cookbook

9.7. Writing Templates with Conditionals and Loops

Problem

Your template needs to iterate over a list of objects and highlight objects if a specific property meets a certain criteria.

Solution

Use a Velocity template with the #foreach and #if directives. The following Velocity template uses a #foreach to loop through a List of Airport beans and an #if to check for the location of an airport relative to the supplied $countryCode:

The World's Busiest Airports

<table>
  <tr>
    <td>Rank</td><td>Code</td><td>Name</td><td>Passengers</td>
    <td>${countryCode} Domestic</td>
  </tr>
  #foreach( $airport in $airports )
    <tr>
      <td>$velocityCount</td>
      <td>$airport.code</td>
      <td>$airport.name</td>
      <td>$airport.passengers</td>
      #if( $airport.countryCode == $countryCode )
        <td>Y</td>
      #else
        <td>N</td>
      #end
    </tr>
  #end
</table>

To render this template, a List of Airport objects and a countryCode String is created and put into a VelocityContext. The $countryCode reference is used to test the countryCode property of every Airport object in the List; if the countryCode property matches, a Y is placed in the last column. The following code initializes the Velocity engine, creates a VelocityContext, and renders the template:

import org.apache.velocity.Velocity; import org.apache.velocity.app.VelocityContext; // Initialize Velocity with default properties Velocity.init( ); // Create a List to hold our Airport objects List airports = new ArrayList( ); airports.add( new Airport(1, "ATL", "Hartsfield Atlanta", 76876128, "US" ...