Jakarta Commons Cookbook

9.9. Invoking Methods in a Template

Problem

You need to invoke methods from a Velocity template.

Solution

Use Velocity to access public methods on an object in the VelocityContext. Bind an object to the VelocityContext and reference methods on these objects in a Velocity template. The following template, available on the classpath at scripting/velocity/results.vm, invokes the average( ), min( ), and max( ) methods on a StatUtil object bound to the reference $stat:

** Aggregate Statistics

Average: $stat.average( $results.scores )%
Lowest: $stat.min( $results.scores )%
Highest: $stat.max( $results.scores )%

** Scores:
#foreach( $student in $results.students )
    #score( $student 50 )
#end

More results are available here:
http://www.test.com/detail?test={results.id}

The StatUtil object, which is bound to $stat, computes basic statistics on integer arrays. This class definition is:

public class StatUtil {
    public int average(int[] array) {
        int sum = 0.0;
        for( int i = 0; i < array.length; i++ ) {
            sum += array[i];
        }
        return( sum / array.length );
    }

    public int min(int[] array) {
        int min = Integer.MAX_VALUE;
        for( int i = 0; i < array.length; i++) {
            if( array[i] < min) { min = array[i]; }
        }
        return( min );
    }

    public int max(int[] array) {
        int max = Integer.MIN_VALUE;
        for( int i = 0; i < array.length; i++) {
            if( array[i] > max) { max = array[i]; }
        }
        return( max );
    }
}

The template shown above is loaded from the classpath, and a StatUtil object is added to the VelocityContext . The VelocityEngine is configured ...