Employment/Purpose

Here we describe how to make a ZUL page to be assembled at the client by using Ajax to request ZUL pages separately in a foreign templating framework1.

You could skip this chapter if you’d like to use ZK’s templating technology, such as Templating: composition, Servlet’s inclusion (javax.servlet.RequestDispatcher’s include) and macro components.

ZK also supports many powerful layout components, such as portallayout, borderlayout, tablelayout, columnlayout and so on2. You could use them to have similar or better effect, and skip this chapter.

Prerequisite

DOCTYPE

To use ZK components correctly, the templating page must specify DOCTYPE as follows.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html>
...

Browser Cache

Though optional, it is suggested to disable the browser to cache the result page. It can be done as follows.

<html xmlns="http://www.w3.org/1999/xhtml">
  <head>
    <meta http-equiv="Pragma" content="no-cache" />
    <meta http-equiv="Expires" content="-1" />

Make a ZUL page as a fragment

Include a ZUL page when receiving a request

By default, if a ZUL page is requested by the browser directly, it will generate a complete HTML structure, including HTML, HEAD and BODY tags. On the other hand, if the assembling is done by inclusion (javax.servlet.RequestDispatcher’s include), a ZUL page will be generated as a HTML fragment without HTML, HEAD, and BODY. For example, if a ZUL page is included by jsp:include, then it won’t generate HTML/HEAD/BODY, such that the following JSP page will be rendered correctly.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<%-- a JSP page --%>
<html>
  <body>
    <jsp:include page="frag.zul"/>
...

In other words, if the result page is assembled when the request is received, you don’t need to do anything specially3. However, if the assembling is done at the client side by using Ajax to request fragments after loaded, you have to read the following section.

Load a ZUL page with an Ajax request

As described above, if a ZUL page is requested by the browser directly, it will, by default, generate a complete HTML structure, including HTML, HEAD and BODY tags. To disable it, you could specify a special parameter called zk.redrawCtrl=page. For example, you might have a HTML page that loads a ZUL page at the client with jQuery as follows.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
    <head>
        <title>Mash-up of ZUML apges</title>
        <script src="http://code.jquery.com/jquery-1.4.2.min.js">
        </script>
    </head>
    <body>
        <div id="anchor"></div>
        <button onclick="$('#anchor').load('foo.zul?zk.redrawCtrl=page')">Load the fragment</button>
    </body>
</html>

The zk.redrawCtrl parameter is used to control how a ZUL page is specified. In this case, since page is specified, the generation of HTML, HEAD and BODY tags are disabled.

Alternative: using the request-scoped attribute called org.zkoss.zk.ui.page.redrawCtrl

If a ZUL page is always loaded as a fragment by the client, you could specify the request-scoped attribute called org.zkoss.zk.ui.page.redrawCtrl (org.zkoss.zk.ui.sys.Attributes#PAGE_REDRAW_CONTROL) with page, such that the generation of HTML, HEAD and BODY tags are always disabled no matter if the zk.redrawCtrl parameter is specified or not.

For example,

<window title="whatever content you want"/>
  <custom-attributes scope="request" org.zkoss.zk.ui.page.redrawCtrl="page"/>
  ...
</window>

Then, you don’t need to specify the zk.redrawCtl parameter when loading it at the client (e.g., $('#anchor').load('foo.zul')).

Of course, if the fragment itself is a JSP page and then use inclusion to include a ZUL page (or use ZK JSP Tags), then the generated HTML structure is already a correct HTML fragment (and you don’t need to anything described above).

Server-side memory optimization: turn off browser cache

As described in Use ZK in JSP, the memory footprint at the server can be improved by turning off the browser cache for the HTML page that will load ZUL pages later. For example, we could add no-cache and expires as follows (line 4 and 5):

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
    <head>
        <meta http-equiv="Pragma" content="no-cache" />
        <meta http-equiv="Expires" content="-1" />
        <title>Mash-up of ZUML apges</title>
        <script src="http://code.jquery.com/jquery-1.4.2.min.js">
        </script>
    </head>
    <body>
        <div id="anchor"></div>
        <button onclick="$('#anchor').load('foo.zul')">Load the fragment</button>
    </body>
</html>

In addition, we have to specify a request-scoped attribute called org.zkoss.zk.desktop.nocache in the ZUL page being loaded as follows:

<window title="whatever content you want"/>
  <custom-attributes scope="request" org.zkoss.zk.desktop.nocache="true"
    org.zkoss.zk.ui.page.redrawCtrl="page"/>
  ...
</window>

Note: since 5.0.8, assigning page to the zk.redrawCtrl parameter implies no-cache, i.e., zk.redrawCtrl=page implies org.zkoss.zk.desktop.nocache="true".

ID Generator

Each ZUL page we request by Ajax as described above will be an independent desktop. It means the browser window will have several desktops, if we assemble UI this way. Thus, the component’s UUID must be unique across different desktops (of the same session4). The default ID generator can handle it well.

However, if you use a customized org.zkoss.zk.ui.sys.IdGenerator, you have to generate component’s UUID (org.zkoss.zk.ui.sys.IdGenerator#nextComponentUuid(org.zkoss.zk.ui.Desktop, org.zkoss.zk.ui.Component)) correctly. A typical trick is to encode desktop’s ID as part of component’s UUID.

Communicate among ZUL pages

If a ZUL page is loaded separately with Ajax, an independent desktop is created. For example, the following HTML page will create three desktops.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Pragma" content="no-cache" />
<meta http-equiv="Expires" content="-1" />
<script type="text/javascript"
    src="http://code.jquery.com/jquery-1.4.2.js"></script>

<title>Assembling at the client with Ajax</title>
</head>
<body>
<table>
    <tr>
        <td id="top" colspan="2">top</td>
    </tr>
    <tr>
        <td id="left">left</td>
        <td id="right">right</td>
    </tr>
</table>
<script>
    $(function() {
        $.get("/frags/banner.zul", 
                {width : "600px"}, 
                function(response) {
                  $("#top").html(response);
            }
        );
        $.get("/frags/leftside.zul",
                {width : "300px"},
              function(response) {
                  $("#left").html(response);
              }
        );
        $.get("/frags/rightside.zul",
            {width : "300px"},
            function(response) {
              $("#right").html(response);
            }       
        );
    });
</script>
</body>
</html>

Since they are in different desktops, you have to use the group-scoped event queue5 if you want to send events from one desktop (such as leftside.zul) to another (such as rightside.zul). For more information, please refer to Event Queues.

Version History

Version Date Content
5.0.5 October, 2010 ZUL page is able to be generated as a HTML fragment.

  1. Apache Tiles is a typical templating framework and allows developers to assemble UI at both server and client. ↩

  2. For more information, please refer to ZK Component Reference. ↩

  3. You might take a look at Use ZK in JSP for more information. ↩

  4. In short, component’s UUID must be unquie in the same session. It is OK to be duplicated in different session. ↩

  5. The group-scoped event queue is available only in ZK EE. For ZK CE, you have to use the session-scoped event queue. ↩