ZK Getting Started/Get ZK Up and Running with MVC

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Introduction

This tutorial is intended for software developers who have experience in writing Java program with Eclipse. We will guide you how to build a modern web application with ZK. The target application we are going to build is a simple bookstore catalog application. You will also learn basic concepts of ZK during this tutorial.

You can take look at [http:// target application's live demo].

We also provide the complete source code with an Eclipse project zip file in Download section. To run the application please refer to Run on Server

Installation

Prerequisite

We use Eclipse IDE 3.7 (indigo) for Java EE developer (Download Eclipse) to demonstrate the whole instructions.

Create a Web Project

Open Eclipse.

1. select File \ New \ Dynamic Web Project
2. enter zktutorial in Project name and keep every thing else default.

Download

Download the ZK CE (file name should be zk-bin-6.0.2.zip) and extract it to a folder.

Add ZK JAR to Your Project

To use ZK in your project, you have to copy ZK JAR into your project's library folder.

Copy JAR files under following list to zktutorial/WEB-INF/lib:

• {YOUR_ZK_UNZIP_FOLDER}/dist/lib
• {YOUR_ZK_UNZIP_FOLDER}/dist/lib/ext

Create a Simple Page

After installation, you can create a simple zul to verify the installation works or not. In Eclipse,

1. select File / New / File or File / New / Other / File to add a new file, hello.zul, under WebContent.
2. Copy and paste the following sample code into hello.zul and save it.

hello.zul

 <window title="My First ZK Application" border="normal">
 	Hello World!
 </window>

Run on the Server

Right click on hello.zul, in context menu, select Run As / Run on Server to run this zul on an application server.

If you have defined servers before, choose an existing server. If you don't, select Manually define a new server and select Tomcat v7.0 Server . Then click "Next".

If you have installed Tomcat before, just provide your path. If you don't, proceed the following step:

1. click Download and Install button and choose a folder
2. accept the license agreement, wait for a minute.

   Eclipse will download and install Tomcat into the folder you specified. After installation is complete, the Finish button will become enabled.

3. Click Finish button to wait for server starting.

Eclipse opens an internal browser automatically and connects to http://localhost:8080/hello.zul. If you can see the following image, then your installation is success.

If you prefer to use Tomcat 6, please refer to ZK Installation Guide.

Example Application

Our target application is a simple bookstore catalog application. This application only has 2 main functions:

1. Search books.

   Enter a keyword in the textbox on the upper part of a window, click search button and it displays the search result in the book list below.

2. View details.

   Click any item of the book list, then the area below the book list shows the selected book's detail data including name, price, description, and cover preview.

The following is the domain object that represents a book.

public class Book {
	private Integer id;
	private String name;
	private String thumbnail;
	private String description;
	private Float price;
	//omit getter and setter for brevity
}

• The "thumbnail" property stores the absolute path of book cover preview image.
• Please refer to References section to see the complete code.

Then we define a service class to perform the business logic (search books) as follows:

public interface BookService {

	/**
	 * Retrieve all books in the bookstore.
	 * @return all books
	 */
	public List<Book> findAll();
	
	/**
	 * search books according to keyword.
	 * @param keyword book name's keyword
	 * @return list of book that match the keyword
	 */
	public List<Book> search(String keyword);
}

• The implementation detail is not in this article's scope, please refer to References section.

Sketch User Interface

Design UI is a good step to start building an application, since it helps you define the scope of your application. ZK provides hundreds of ready-made UI components. Developers can rapidly build their desired own user interface by combining these components without creating from scratch.

In ZK, you can use ZK User Interface Markup Language (ZUML) , an XML-formatted language, to describe user interface. In ZK default convention, the files to describe user interface use .zul as file name suffix. One XML element (tag) represents a component, and each component's style, behavior, and function can be configured by setting XML element's attributes. For example, the following code is a window with specified title and normal border of our example application.

Extracted from search.zul

	<window title="Search Product" width="800px" border="normal" style="padding-top:10px;padding-left:10px;">
		<!-- put child components inside a tag's body -->
	</window>

We use a window as our application's frame. As it is the outmost component, it's called the root component. Window is a mostly common used container because it's a basic display element of a desktop-like application and it can also encloses other components. All other components inside the window should be put in window tag's body, and they are called child component. Window has several display modes. By default, it is in the embedded mode. We set window's title bar text with "title" attribute and make window display a normal border with "border" attribute. For "width" attribute, use CSS like syntax such as "800px", "60%". The "style" attribute allows you to customize component's style with CSS syntax.

Basically, our example application's user interface is divided into 3 areas inside a window, they are (from top to bottom) search function, book list, and book details area.

search

book list

book details

Search Area. ZK components are like building blocks, you can combine existing components to construct your desired user interface. To allow users to search, we need a place to enter keywords, a button for triggering search, and a text to tell user what they should input. We can use following zk components to fulfill this requirement:

Extracted from search.zul

	 	<hbox align="center">
	 		<label>Book Name Keyword:</label>
	 		<textbox id="keywordBox" />
	 		<button id="searchButton" label="Search" image="/img/search.png" />
	 	</hbox>

The hbox ("h" means horizontal) is a layout component and it can arrange its child components in horizontal order. Because these three child components have different height, we use "align" attribute to arrange them for elegance. Here we specify "id' attribute for some components in order to control them, and we'll talk about the reason in next section. You can easily create an image button by specifying path at "image" attribute.

Book List Area. ZK provides several components to display a collections of data such as listbox, grid, and tree. We use listbox to display a list of book with 2 columns: Name and Price. The "rows" attribute is used to control how many rows are visible and you can drag scroll-bar to see the rest of rows. The listbox is a container component, and you can add listhead to define a column. The listitem is used to display data, and the number of listcell corresponds to the number of listheader.

Extracted from search.zul

	 	<listbox id="productListbox" rows="5">
			<listhead>
				<listheader label="Name" />
				<listheader label="Price" />
			</listhead>
			<listitem>
				<listcell value="product name"></listcell>
				<listcell>$<label value="price" /></listcell>
			</listitem>
		</listbox>

Book Details Area. Like the hbox, vbox is a layout component which arranges its child component in vertical order. By combing these 2 layout components, we can present more information on a screen.

Extracted from search.zul

		<hbox style="margin-top:20px">
			<image id="thumbImage" width="250px" />
			<vbox>
				<label id="nameLabel" />
				<label id="priceLabel" />
				<label id="descriptionLabel"/>
			</vbox>
		</hbox>

You can see complete zul through the link in reference section.

Control Components

The next step after sketching the UI is to make UI response to users. In ZK, we have 2 approaches to design an application, the first approach we introduce here is to control ZK UI component (Java object) directly by yourself in a controller. This approach can be classified to Model-View-Controller (MVC) design pattern. This approach divides an application into three parts.

The Model consists of application data and business rules.BookService and other classes used by it represent this part in our example application.

The View means user interface. The zul page which contains ZK components represents this part. An user's interaction with components triggers events to be sent to controllers.

The Controller plays as a coordinator between View and Model. It receives events from View to update Model and retrieve data to change View's presentation. ZK composer represents this part.

1. When a user interacts with a component (e.g. click a button) on a ZUL, the user's action triggers an event.

   This event is sent to ZK composer (controller) and invoke users-implemented event listener method.

2. The event listener that is corresponding to the component is invoked.
3. The event listener method usually executes business logic or accesses data, then manipulate ZK components.
4. Component's change made in event listeners reflects to UI change.

In this chapter, you'll learn:

1. How to handle a component's event
2. How to control components in a composer
3. How to use template

UI Controller

In ZK, the controller is responsible for controlling ZK components and listening events which are triggered by user interaction.

In order to control UI in ZK, you have to implement a controller class for a ZUL. You can simply extends SelectorComposer :

package tutorial;

// omit import for brevity

public class SearchProductComposer extends SelectorComposer<Component> {

}

After a composer is implemented, you should associate it to a component in a zul file, so that the composer can control the component including its child components. Associating a composer to a component is just specifying full-qualified class name in target component's apply attribute. The following code shows how to associate a composer to a window.

	<window title="Search Product" width="800px" border="normal" style="padding-top:10px;padding-left:10px;"
	apply="tutorial.SearchProductComposer">
	<!-- omit other components for brevity -->
	</window>

Declare Event Listener

We want search() to be invoked when "Search" button is clicked, so we can specify the relationship with syntax:

@Listen("[EVENT_NAME] = #[COMPONENT_ID]").

The final code looks like:

	@Listen("onClick = #searchButton")
	public void search(){
		String keyword = keywordBox.getValue();
		productListbox.setModel(new ListModelList<Book>(bookService.search(keyword)));
		System.out.println(keyword);
	}

• Line 1: There are other syntax to specify @Listen's parameter.
• Line 5: This line is used to verify the method is called.

Now, run search.zul on the server, enter a keyword, click "Search" button. You'll find your console prints the keyword you type.

When we associate a composer to a component, every event triggered by this component (and its child components) is sent to the composer. If there is a event listener method that corresponds to the component's event, it will be invoked. When a user interact with a component, ZK sends events automatically upon user's actions. For example, click a button issues an "onClick" event, select an item in a listbox issues an "onSelect" event. You don't need to worry about events generating.

What you should do to handle an user's action:

1. Get UI components you want to control.
2. Write a method to implement UI changing logic
3. Specify which component's event this method listener

Search Books According to above steps, to implement search function, we need to:

1. Get the textbox for entering keyword
2. Get the keyword value and pass to BookService to search for result.
3. Make the method listen "Search" button's "onClick" event.

Control ZK Component

One of SelectorComposer's features is allowing you to retrieve the UI component's object by annotating @Wire on controller's member variables.

Steps:

1. Declare a variable with corresponding component type (e.g. Listbox, Label...)
2. Variable's name is the same as component's id.
3. Annotate the variable with @Wire.

Then SelectorComposer will "wire" a corresponding ZK component object to the variable you declared. After this has been done, you can then control and manipulate UI by accessing those annotated member variables.

public class SearchProductComposer extends SelectorComposer<Component> {

	@Wire
	private Listbox productListbox;

	//other codes...
}

• In mentioned search.zul, there is a listbox whose id is "productListbox". SelectorComposer will make productListbox reference to the listbox object after components are created.

This method performs simple logic: call book service class to search with keyword and set result list to listbox. For a variable which references to a component, we can get data from zul such as user's input, or a button's visibility with getter (e.g. getValue()) or change it status like making a label red with setter to achieve some dynamic UI effect. Hence, we can easily get what keyword a users input by keywordBox.getValue() and change data item of listbox by productListbox.setModel() .

	//omit codes to get components

	public void search(){
		String keyword = keywordBox.getValue();
		List<Book> result = bookService.search(keyword);
		productListbox.setModel(new ListModelList<Book>(result));
	}

• Line 6: Notice that setModel() only accepts ListModel object. Because our service class return a List object, we use ListModelList to wrap search result list. There are other ListModel object for different collection types, please refer to reference section.

Use Template

We have successfully made "Search" button invoke event listener, but you still find that content of listbox doesn't show search result. That is because we don't specify how to render data model of listbox. Now, we will use a special tag, <template> to control the rendering of each item. ZK will render template tag's content repeatedly for each object in model of listbox.

Steps:

1. Use <template> to enclose components that you want to render repeatedly.
2. Set template's name attribute to "model".
3. Use implicit variable each to assign domain object's properties to component's attributes.

   The "each" is a variable that references to a domain object in the model list, you can use it to access domain object's property with EL, e.g. ${each.name}

	 	<listbox id="productListbox" rows="5">
			<listhead>
				<listheader label="Name" />
				<listheader label="Price" />
			</listhead>
			<template name="model">
				<listitem>
					<listcell label="${each.name}"></listcell>
					<listcell>$<label value="${each.price}" /></listcell>
				</listitem>
			</template>
		</listbox>

• Line 5: The template tag's "name" attribute should be model and be declared inside the listbox.
• Line 8: The implicit variable ${each}" represents an object of the model which is Book in our example application.

Implement View Details Function

The steps to implement view details function is similar to search. We use @Wire to get components including thumbImage, nameLabel, priceLabel, and descriptionLabel and stuff data to them with setter in a method. Then declare that method to listen "onSelect" event of listbox with @Listen. Notice that when implement a event listener, it can have an Event object as its parameter. It's optional. If you declare in your method's signature, ZK will pass corresponding event object. In our case, we can get selected book from event object to retrieve book's details.

	@Listen("onSelect = #productListbox")
	public void showDetail(SelectEvent event){
		Book selectedBook = (Book)event.getSelectedObjects().iterator().next();
		thumbImage.setSrc(selectedBook.getThumbnail());
		nameLabel.setValue(selectedBook.getName());
		priceLabel.setValue("$"+selectedBook.getPrice());
		descriptionLabel.setValue(selectedBook.getDescription());
		
	}

Line 2: The "onSelect" event corresponds to SelectEvent, and you can know it from Javadoc.

For complete source code, please refer to Reference section

Data Binding

The second approach to handle user interaction is to let ZK control UI component for you. This approach is classified to Model-View-ViewModel (MVVM) design pattern. This approach also divides an application into three parts. Only ViewModel is the different part from MVC. The ViewModel acts like a special Controller for the View which is responsible for exposing data from the Model to the View and for providing required action and logic for user requests from the View. The ViewModel is type of View abstraction, which contains a View's state and behavior. But ViewModel should contain no reference to UI components and knows nothing about View's visual elements.

ViewModel

In ZK, ViewModel can be simply a POJO, and it usually should not contain any variable which references to UI components.

Steps to associate a ViewModel to a zul:

1. Implement a ViewModel class
2. Set attribute apply="org.zkoss.bind.BindComposer" to a target component
3. Set attribute viewModel="@id('VIEWMODEL_ID')@init('CLASS_NAME')"

Creating a ViewModel is like creating a POJO, and it exposes its properties like JavaBean through setter and getter methods.

public class SearchViewModel{
	//declare properties, setter, and getter methods
}

We can bind ZK UI component to a ViewModel by setting its viewModel attribute, and that component becomes the Root View Component for the ViewModel. All child components of this Root View Component can acces the same ViewModel and its properties. To bind a ViewModel, we have to apply a composer called org.zkoss.bind.BindComposer, it will create a binder for the ViewModel and instantiate the ViewModel's class. Using ZK Bind annotations then we set viewModel attribute with the ViewModel's id in @id and the ViewModel's full-qualified class name in @init . The id is used to reference ViewModel's properties, e.g. vm.name, whilst the full-qualified class name is used to instantiate the ViewModel object itself.

	<window title="Search Product" width="800px" border="normal" style="padding-top:10px;padding-left:10px;"
		apply="org.zkoss.bind.BindComposer" viewModel="@id('vm')@init('tutorial.SearchViewModel')">
	<!-- omit other tags-->
	</window>

Binding Properties to Component Attributes

public class SearchViewModel {

	private String keyword;

	public void setKeyword(String keyword) {
		this.keyword = keyword;
		System.out.println(keyword);
	}
}

		<hbox>
			<label>Book Name Keyword:</label>
			<textbox value="@save(vm.keyword)" />
			<button label="Search" image="/img/search.png" />
		</hbox>

User Actions as Commands

public class SearchViewModel {

	private List<Book> bookList;
	
	private String keyword;
	
	public List<Book> getBookList(){
		return bookList;
	}
	
	@Command
	public void search(){
		bookList = bookService.search(keyword);
		for (Book b: bookList){
			System.out.println(b.getName());
		}
	}
}

		<hbox>
			<label>Book Name Keyword:</label>
			<textbox value="@save(vm.keyword)" />
			<button label="Search" image="/img/search.png" onClick="@command('search')" />
		</hbox>

Unit Test ZK Application

ZK provides a unit test library, Mimic, which is one module of ZK Application Test Suite (ZATS).

Download

[Example application zip file]