I have a list of Player objects getting passed into a JSP from a controller, and I want to display them in a couple of different ways on the same page:
I could put separate sorted copies in the model, but dealing with different ways to display the same list seems more like a responsibility of the view, so I'd like to avoid putting the logic in the controller if I can. I already have a couple of classes implementing Comparator to help with the actual sorting.
What's the best way to do that in a JSP?
Can I sort the list before passing it in to the different forEach
tags?
The SO EL Tag Wiki describes a way to do this without using a scriptlet: using an EL function to do the sort, then using the result for the items
attribute in the JSTL core forEach
tag.
The function class:
package org.hierax.ifdl.tags.player;
public final class PlayerSort {
public static List<Player> sortByRank(List<Player> playerList) {
Collections.sort(playerList, new PlayerSortByRank());
return playerList;
}
public static List<Player> sortByAlias(List<Player> playerList) {
Collections.sort(playerList, new PlayerSortByAlias());
return playerList;
}
}
The TLD:
<?xml version="1.0" encoding="UTF-8" ?>
<taglib
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd"
version="2.1">
<display-name>Player Functions</display-name>
<tlib-version>1.0</tlib-version>
<short-name>player</short-name>
<uri>org.hierax.ifdl.tags</uri>
<function>
<name>sortByRank</name>
<function-class>org.hierax.ifdl.tags.player.PlayerSort</function-class>
<function-signature>java.util.List sortByRank(java.util.List)</function-signature>
</function>
<function>
<name>sortByAlias</name>
<function-class>org.hierax.ifdl.tags.player.PlayerSort</function-class>
<function-signature>java.util.List sortByAlias(java.util.List)</function-signature>
</function>
</taglib>
The menu JSP:
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ taglib prefix="p" uri="/WEB-INF/player.tld" %>
<h1>Players</h1>
<p>
<c:forEach items="${p:sortByAlias(model.players)}" var="player">
<a href="<c:url value="/player/${player.id}"/>" class="menuItem">${player.alias}</a>
</c:forEach>
</p>
Employ Collections.sort(List, Comparator), providing your own Comparator as required to sort the list into the right order. The java, which could be embedded within <%
and %>
tags, would look something like:
List<Player> list = new ArrayList<Player>();
list.add(new Player()); // populate list
list.add(new Player()); // etc
Collections.sort(list, new Comparator<Player>() {
public int compare(Player o1, Player o2)
{
return o1.getName().compareTo(o2.getName()); // Compare by name, for example
}});
// Now iterations on list will be in 'name' order
for (Player player : list) {
// Display player
}
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