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  • Author
    Timothy Clare, Potix Corporation
  • Date
    May, 2015
  • Version
    ZK 8.0.0 RC



The ZK team is proud to announce the release of ZK 8!

ZK 8's main focus was on improving

Download and Demo

Support Expression Language 3 (EL3)

  • Available for ZK:
  • ce-pe-ee.png

introduce the new generation expression language of Java EE 7 – Expression Language 3 (EL 3) into ZK 8 so we can do more complicated and more powerful things with the newer expression language. There are many new features in EL 3 such as new operators, lambda expressions and collection operations. For more information on EL3 please take a look at the specification, JSR-341.

Please note that EL3 and all its features (including Lambda expressions) work for JDK 5 and above.

Lambda Expressions

Each converter is implemented with the capability to interpret lambda expressions defined in zul. The following shows an example of a textbox who's value and onOK command are both driven by lambdas.

<textbox value="@load((x -> (x * 100) / 2.54)(vm.value))" 
    onOK="@command('click', key=((x -> (x * 2.54) / 100)(self.value)))" />

The syntax used is same as ones in Java SE 8 and behaves like an anonymous function which is discarded after evaluated. We can name a lambda and evaluate indirectly.

Let us take the lambda expression (x -> (x * 100) / 2.54). In this case it will create an anonymous function which takes a value, multiplies it by 100 and divides the result by 2.54. This function is then applied to vm.value, where vm stands for our viewmodel.

To simplify this let us write some psuedo code for demonstration purposes.

myFunction = x -> (x * 100) / 2.54 //assign a lambda to myFunction temporarily
myFunction(vm.value) //execute myFunction passing vm.value as the parameter

While the above is just pseudo code to better help you understand the functionality it does demonstrate naming of lambdas, which is also possible. The following section outlines how to do this using two new operators.

New Operators

String Concatenation

String concatenation has been introduced to make it easy to construct strings within EL expressions. The following code snippet demonstrates how to do so.

<label value="@load(('Hi, ' += vm.firstname += ' ' += vm.lastname))" />

Assignment and Semicolons

Both assignment and semicolon operators are now implemented. Below shows an example of both being used.

<label value="@load((incr = x -> x + 1; incr(5)))" />

The assignment operator in this instance assigns a lambda function to incr which takes x, increments by 1 and then returns it.

incr = x -> x + 1

By using the ';' operator it evaluates the left hand side first, thus creating a lambda function incr, as previously discussed. Then evaluates and returns the right hand side. So in the following case:

<label value="@load((incr = x -> x + 1; incr(5)))" />

The value assigned to the label would be 6, as the lambda function is first evaluated and assigned to incr, then the incr(5) call is evaluated leading to a return value of 6.

Collection Operations

In ZK 8 it is now possible to use collection chain operations directly. In the example below we turn vm.names into stream() and then can create a pipeline of commands.

<listbox model="@load((
                               .filter(x -> x.contains(vm.filter))

In addition to pipelines ZK 8's EL 3 supports easy collection construction using brackets ([ ]). The following example demonstrates this.

<label value="@load(([1, 2, 3, 4].stream().sum()))" />

Static Field and Method References

A static field or static method of a Java class can be referenced with the syntax Classname.Field, such as

<label value="@load((Math.sqrt(16)))" />

Please note that java.lang.* is imported by default.

Major MVVM Enhancements

Performance Increase

ZK 8 has brought about increases in MVVM binding performance, with both a memory consumption decrease and a response time increase. Below is the graph outlining these performance changes.

Memory improvements

ZK 8.0.0 RC requires much less memory than ZK 7.0.5 EE giving your application a boost just by upgrading. The graph plots the number of users against the memory used, where the lower the better.


Response Improvements

ZK 8.0.0 RC MVVM also responds quicker than ZK 7.0.5 EE. The graph below plots the number of users against the response time, where the lower the response time the better.


Recreating the tests

If you would like to recreate these tests above in your environment you can use the following code:

Java code

package org.zkoss.test;
import java.util.Collections;
import java.util.List;
public class ForEachVM {
	private List<Integer> array = Collections.nCopies(30, 30);
	public void setArray(List<Integer> array) {}
	public List<Integer> getArray() {
		return array;


<zk xmlns:x="xhtml">
	<div id="bind" apply="org.zkoss.bind.BindComposer"
		viewModel="@id('vm') @init('org.zkoss.test.ForEachVM')">
		<div style="display:none" id="host">
			<div children="@load(vm.array)">
				<template name="children">
				<div children="@load(vm.array)">
					<template name="children">
					Test Label


ZK 8 brings about a change to the notify system. You are all used to @NotifyChange, however, ZK 8 has a better way, @SmartNotifyChange. Essentially the usage is exactly the same as @NotifyChange, except it will only notify the binder when a value has changed, unlike @NotifyChange. Thus it is more performant.

The following shows some example code:

public class OrderVM {

    //other code...

    //action command
    public void newOrder(){
        Order order = new Order();
        getOrders().add(order); //add new order to order list
        selected = order;//select the new one

For more information please consult the ZK MVVM book and the new form binding blog.

MVVM support at the client

After listening to feedback the ZK team has introduced functionality in ZK 8 which allows developers to access ViewModel properties at the client. The following couple of code snippets demonstrates how to use this functionality.

Publishing a command using native component or direct invocation

<xhtml:button n:onClick="@command('doClick', {key:value, key1:valul1})"/>
wgt.$binder().command('doClick', args);

Subscribing to commands

wgt.$binder().after('commandName', callbackFuncation);

For more information please take a look at the ZK 8 Series Smalltalk.

BindingParam annotation supports converting from JSON to POJO automatically

ZK 8 now supports the ability to convert JSON sent to ZK into objects at the server automatically. Consider this example.

zkbind.$(someone).command('dataChange', {data:{title: "myData"}});

The above code will send JSON data to the command function "dataChange", this can be automatically converted into an appropriate object using the BindingParam.

public static class DataObject {
	private String title;
	public void setTitle(String title) {
		this.title = title;
	public String getTitle() {return title;}

public void dataChange(@BindingParam("data") DataObject data) {
	// do something here.

For more information please visit INSERT LINK HERE.

Children binding supports list model

In ZK 8, children binding supports a ListModel! This means you can separate the View and Model by implementing ListModel, which is used to provide data. Additionally, when you add/update/remove the data in the model, the corresponding components in children binding will be re-rendered at the same time.

When using List in children binding, to update data you have to use @NotifyChange to notify the binder any property changes, and the whole rendered components in children binding will be re-rendered at the same time.

The following example outlines the usage.

<vlayout children="@load(vm.model)">
  <template name="children">
private ListModelList model = new ListModelList();

public void add_model() {
  Product newProduct = new Product(++count, "Microwave oven", 999);

For more information please take a look at our blog series on ZK 8 data binding.

FormattedTimeConverter introduced

ZK 8 has introduced a new converter named formattedTime. This makes it extremely easy to output a specific time using a specified format. The following shows an example of usage.

<label value="@load(item.time) @converter('formattedTime', format='hhmmss')"/>

For more information please refer to our ZK MVVM book.

New components & enhancements

Lightweight rich editor

ZK 8 introduces a brand new lightweight component called Tbeditor, representing the JavaScript component Trumbowyg. Tbeditor is a rich WYSIWYG text editor.

The following is an example of how to use Tbeditor in your application.

Zkcompref tbeditor.png

<tbeditor id="tb" value="this is a demo for &lt;b&gt;trumbowy&lt;/b&gt; editor!!" />

For more information please consult the ZK Component Reference.

Timepicker Component

ZK 8 introduces a new component to handle times. The component also has a lot of functionality such as minimum & maximum times along with formatting.

ZKCompRef Timepicker.png

 <window title="Simple" width="300px" border="normal">
     <timebox id="tb0"/>

For more information please consult the ZK Component Reference.

Scrollview component


The Scrollview component, first introduced in ZK 6.5, has been updated in ZK 8 to provide two important events.

  • onScroll
  • onScrolling

The onScroll event notifies the application that the area has been scrolled by the user, and allows developers to check whether said scrolling is outside or inside the components boundaries.

The onScrolling event denotates that the user is scrolling a scrollable component.

For more information please consult the ZK Component Reference.

Shadow Elements

ZK 8 introduces a new concept called Shadow Element.

In simple terms shadow elements help application developers to compose an html layout with some dynamic data. They are basically templates, however, with shadow elements it helps the application to manage templates and their implementation that are outside of the component tree. Thus a shadow element is not visible to users but is handled by ZK.

A web designer can pre-define a template based on HTML syntax for application developers to use.

For example,

    <if test="${user.editable}">
        User Name: <textbox value="${}"/>
        <forEach items="${user.phones}" var="phone">
            <label value="${phone.number}"/>

Shadow Diagram.PNG

As shown in the diagram above, the tree is separated into two parts - Logical Tree and Composed Tree.

  • Logical Tree is created by ZK page parser to construct a page definition tree and then instantiate it into a "Composed Tree".
  • Composed Tree is also separated into two parts, one is the component tree (green area) which is the same as before, and the other is the new concept (red area) shadow tree, which is not visible for application developers but component developers.

The shadow tree in the example above with EL expression won't be alive once the output is rendered to the client. This is because shadow elements are not applied with dynamic data such as @load expressions, so there is no reason to store them in the server side to burden the memory consumption.


To give an example of the power available, the following demo outlines the an application using 3 dataviews (grid, list and tree) using the same dataset and codebase.

To fully understand the power of shadow components, please refer to the ZK 8 Series Smalltalk.

Custom data attribute handlers are now possible

It is possible to define custom data-handlers for client attributes which gives extra flexibility to developers looking to integrate with, and use, 3rd party libraries.

For example, the following demonstrates a data-handler for jQuery's mask functionality.

Zul File:

<textbox xmlns:ca="client/attribute" ca:data-mask="00:00:00" onChange='Clients.log(self.value)'/>


		<name>mask</name><!-- the attribute name, i.e. data-mask -->
		function (wgt, dataValue) {

			// unformat after onChange event.
			wgt.listen({onChange: function (event) { = jq(this.$n()).cleanVal();

For more information please refer to the ZK ZUML Reference.

Font Awesome upgrade

Font awesome has been upgraded to version 4.3, introducing over 40 new icons. For more details please check the font-awesome website.

Introduced Danish language support

Thanks to our contributor XXXX ZK 8 now provides support for the Danish language.

Other changes

ZHTML component's src attribute supports encoded url in ZUL

ZK 8's ZHTML components now support encoded urls, this makes it much easier to specify images and other urls on the src attribute.

For example:

<x:img xmlns:x="xhtml" src="~./img/spacer.gif" xmlns:c="client" c:onBind='zk.log(this.$n().src)'/>

For more information please refer to the ZK Component Reference.

ZHTML supports dynamic data binding

The textContent attribute now supports dynamic databinding, meaning it is now possible to use MVVM based commands for a textContent attribute. For example:

<label textContent="@load("
	sclass="author-name z-label" />

Simplified thrown exceptions

Exceptions were thrown as UIExceptions and when including templates or similar procedures the resulting stacktrace was exceptionally hard to follow. This also make it difficult to create meaningful error pages for application.

With the advent of ZK 8 this is now gone and exceptions are not wrapped with UIException, they will throw a RuntimeException.

Multiple custom error messages supported for multiple constraints

Previously when defining constraints only the last constraint could have a separate error message. This has now been rectified and every constraint can have its own custom error message.

For example:

<datebox constraint="no empty: please select a date, no future: now or never" />

For more information please refer to ZK's Component Reference.

Datebox calendar now contains a today button

Since ZK 8 the Datebox calendar now contains a today button to easily reset the date.


Embedded types now allowed

When parsing a page sometimes an error would occur when HTML was embedded in a ZHTML page. This is now fixed and the ability to use different parsers depending on the syntax in the page is allowed.

For example, here we have HTML embedded inside ZHTML, no exception will be thrown.

		 <!--[if lte IE 9]>
			<link rel="stylesheet" href="../assets/css/test.min.css" />
<u:window xmlns:u="zul" title="test" id="mainWindow" apply="org.zkoss.bind.BindComposer"
	viewModel="@id('vm') @init('test.MyVM')" height="100%" width="100%">
	&copy Test

ForeachStatus is consistent with JSTL's varStatus properties

ZK's ForEachStatus now has the same properties as varStatus, so it is more intuitive for developers to use as it is what they are used to.

<zk xmlns:n="native">
	<n:h4>1. Test case: forEach="one, two, three, four"</n:h4>
	items = Arrays.asList(new Object[] { "one", "two", "three", "four" });
	<div style="border:1px solid blue">
		<div forEach="${items}">
			${each} Index: ${forEachStatus.index} Count:
			${forEachStatus.count} First: ${forEachStatus.first} Last:
	<div style="border:1px solid red;color:blue">
		<div>one Index: 0 Count: 1 First: true Last: false</div>
		<div>two Index: 1 Count: 2 First: false Last: false</div>
		<div>three Index: 2 Count: 3 First: false Last: false</div>
		<div>four Index: 3 Count: 4 First: false Last: true</div>
	<n:h4>2. Test case: forEach="one, two, three, four" forEachStep="3"</n:h4>
	<div style="border:1px solid blue">
		<div forEach="${items}" forEachStep="3">
			${each} Index: ${forEachStatus.index} Count:
			${forEachStatus.count} First: ${forEachStatus.first} Last:
	<div style="border:1px solid red;color:blue">
		<div>one Index: 0 Count: 1 First: true Last: false</div>
		<div>four Index: 3 Count: 2 First: false Last: true</div>
	<n:h4>3. Test case: forEach="one, two, three, four" forEachBegin="1" forEachStep="3"
	<div style="border:1px solid blue">
		<div forEach="${items}" forEachBegin="1" forEachStep="3">
			${each} Index: ${forEachStatus.index} Count:
			${forEachStatus.count} First: ${forEachStatus.first} Last:
	<div style="border:1px solid red;color:blue">
		<div>two Index: 1 Count: 1 First: true Last: true</div>


Copyright © Potix Corporation. This article is licensed under GNU Free Documentation License.