The sorter (SortTool) allows a user to sort a collection (or array, iterator, etc) on any arbitary set of properties exposed by the objects contained within the collection.
The sort tool is specifically designed to use within a #foreach but you may find other uses for it.
The sort tool can handle all of the collection types supported by #foreach and the same constraints apply as well as the following. Every object in the collection must support the set of properties selected to sort on. Each property which is to be sorted on must return one of the follow:
Primitive type: e.g. int, char, long etc Standard Object: e.g. String, Integer, Long etc Object which implements the Comparable interface.
During the sort operation all properties are compared by calling compareTo() with the exception of Strings for which compareToIgnoreCase() is called.
The sort is performed by calling Collections.sort() after marshalling the collection to sort into an appropriate collection type. The original collection will not be re-ordered; a new list containing the sorted elements will always be returned.
The following example shows how the sorter is mapped in the toolbox.xml file:
<tool> <key>sorter</key> <scope>application</scope> <class>org.apache.velocity.tools.generic.SortTool</class> </tool>
The tool is used as follows:
Single Property Sort #foreach($obj in $sorter.sort($objects, "name")) $obj.name Ordinal= $obj.ordinal #end End Multiple Property Sort #foreach($obj in $sorter.sort($objects, ["name", "ordinal"])) $obj.name, $obj.ordinal #end End
The sort method takes two parameters a collection and a property name or an array of property names. The property names and corresponding methods must conform to java bean standards since commons-beanutils is used to extract the property values.
By default the sort tool sorts ascending, you can override this by adding a sort type suffix to any property name.
The supported suffixes are:
#foreach($obj in $sorter.sort($objects, ["name:asc", "ordinal:desc"])) $obj.name, $obj.ordinal #end
This will sort first by Name in ascending order and then by Ordinal in descending order, of course you could have left the :asc off of the 'Name' property as ascending is always the default.