Tutorial"

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This tutorial guides you through the most fundamental features and concepts of ZK.
 
This tutorial guides you through the most fundamental features and concepts of ZK.
 +
* To create web application, please refer to [http://books.zkoss.org/wiki/ZK_Installation_Guide/Quick_Start/Create_and_Run_Your_First_ZK_Application_with_Eclipse_and_ZK_Studio Create and Run Your First ZK Application with Eclipse and ZK Studio]
 
* For product description, please refer to [http://www.zkoss.org/product/zk the ZK product page] and [http://www.zkoss.org/whyzk/features the feature list].
 
* For product description, please refer to [http://www.zkoss.org/product/zk the ZK product page] and [http://www.zkoss.org/whyzk/features the feature list].
 
* For a real world example, please refer to [[ZK Getting Started/Creating a Database-driven Application|Creating a database-driven application]].
 
* For a real world example, please refer to [[ZK Getting Started/Creating a Database-driven Application|Creating a database-driven application]].
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==Hello World!==
 
==Hello World!==
  
After ZK is installed on your favorite Web server<ref>Please refer to [[ZK Installation Guide]].</ref>, writing applications is straightforward. Just create a ZUML file, and name it as hello.zul<ref>The other way to try examples is to use [http://www.zkoss.org/zksandbox/userguide ZK Sandbox] to run them.</ref>, under one of the Web application's directories just as you would do for an HTML file.
+
After ZK is installed on your favorite Web server<ref>Please refer to [[ZK Installation Guide]].</ref>, writing applications is straightforward. Just create a ZUML file<ref>ZUML [http://books.zkoss.org/wiki/ZUML%20Reference/ZUML]</ref>, and name it as hello.zul<ref>The other way to try examples is to use [http://www.zkoss.org/zksandbox/ ZK Sandbox] to run them.</ref>, under one of the Web application's directories just as you would do for an HTML file.
  
 
<source lang="xml" >
 
<source lang="xml" >
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[[Image:dgGettingStartedHello.zul.png]]
 
[[Image:dgGettingStartedHello.zul.png]]
  
On a ZUML page, an XML element describes what a component<ref>Interface : <javadoc type="interface">org.zkoss.zk.ui.Component</ref> can create while the XML attributes are used to assign values to a component's properties. In this example, a <tt>window</tt> component is created and its <tt>title</tt> is set to <tt>"My First ZK Application"</tt> and its <tt>border</tt> is set to <tt>normal</tt>.
+
On a ZUML page, an XML element describes what a component<ref>Interface : <javadoc type="interface">org.zkoss.zk.ui.Component</ref> can create while the XML attributes are used to assign values to a component's properties. In this example, a <code>window</code> component is created and its <code>title</code> is set to <code>"My First ZK Application"</code> and its <code>border</code> is set to <code>normal</code>.
  
The text enclosed in the XML elements can also be interpreted as a special component called <tt>label</tt>. Thus, the above example is equivalent to the following code:
+
The text enclosed in the XML elements can also be interpreted as a special component called <code>label</code>. Thus, the above example is equivalent to the following code:
  
 
<source lang="xml" >
 
<source lang="xml" >
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[[Image:DgGettingStartedHello2.png]]
 
[[Image:DgGettingStartedHello2.png]]
  
The <tt>onClick</tt> attribute is a special attribute used to add an event listener(<javadoc type="interface">org.zkoss.zk.ui.event.EventListener</javadoc>) to the component such as that it is invoked when an end user clicks the component. The attribute value could be any legal Java code. Notice that it is '''NOT''' JavaScript, and you have to use double quotes (") in a string. To escape a double quote in an XML string, you could use single quotes (') to enclose it<ref>If you are not familiar with XML, you might take a look at [[ZK Developer's Reference/UI Composing/ZUML/XML Background|the XML background section]].</ref>.
+
The <code>onClick</code> attribute is a special attribute used to add an event listener(<javadoc type="interface">org.zkoss.zk.ui.event.EventListener</javadoc>) to the component such as that it is invoked when an end user clicks the component. The attribute value could be any legal Java code. Notice that it is '''NOT''' JavaScript, and you have to use double quotes (") in a string. To escape a double quote in an XML string, you could use single quotes (') to enclose it<ref>If you are not familiar with XML, you might take a look at [[ZK Developer's Reference/UI Composing/ZUML/XML Background|the XML background section]].</ref>.
  
  
 
Here we invoke <javadoc method="show(java.lang.String)">org.zkoss.zul.Messagebox</javadoc> to display a message box shown above.
 
Here we invoke <javadoc method="show(java.lang.String)">org.zkoss.zul.Messagebox</javadoc> to display a message box shown above.
  
The Java code is interpreted by [http://www.beanshell.org/ BeanShell] at runtime. In addition to event handling, you could embed the code in a ZUML page by specifying it in a special element called <tt>zscript</tt>. For example, you could simply define a function in the code as the following:
+
The Java code is interpreted by [http://www.beanshell.org/ BeanShell] at runtime. In addition to event handling, you could embed the code in a ZUML page by specifying it in a special element called <code>zscript</code>. For example, you could simply define a function in the code as the following:
  
<source lang="xml" >
+
<source lang="xml" high="3">
 
  <window title="My First ZK Application" border="normal">
 
  <window title="My First ZK Application" border="normal">
 
  <button label="Say Hello" onClick='alert("Hello World!")'/>
 
  <button label="Say Hello" onClick='alert("Hello World!")'/>
Line 64: Line 65:
 
</source>
 
</source>
  
In fact, <tt>alert</tt> is a built-in function that you can use directly from the embedded Java code.
+
In fact, <code>alert</code> is a built-in function that you can use directly from the embedded Java code.
  
 
<blockquote>
 
<blockquote>
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</source>
 
</source>
  
where [[ZUML Reference/EL Expressions/Implicit Objects/self|<tt>self</tt>]] is a built-in variable which refers a component receiving the event.
+
where [[ZUML Reference/EL Expressions/Implicit Objects/self|<code>self</code>]] is a built-in variable which refers a component receiving the event.
  
If you enter <tt>java.version</tt> and then click the button, the result will be shown as the following:
+
If you enter <code>java.version</code> and then click the button, the result will be shown as the following:
  
 
[[Image:DgGettingStartedProperty.png]]
 
[[Image:DgGettingStartedProperty.png]]
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Instead of introducing different components for different purposes, our components are designed to build blocks. You are free to compose blocks together to realize sophisticated UI without customizing any components. For example, you could put anything in a grid, including grid itself; anything in any layout, including the layout itself. Please see [http://www.zkoss.org/zkdemo our demo] for more examples.
 
Instead of introducing different components for different purposes, our components are designed to build blocks. You are free to compose blocks together to realize sophisticated UI without customizing any components. For example, you could put anything in a grid, including grid itself; anything in any layout, including the layout itself. Please see [http://www.zkoss.org/zkdemo our demo] for more examples.
 +
 +
==Express data with variable resolver and EL expressions==
 +
 +
On a ZUML page, you could locate data with a variable resolver (<javadoc type="interface">org.zkoss.xel.VariableResolver</javadoc>), and then express it with [[ZK Developer's Reference/UI Composing/ZUML/EL Expressions|EL expressions]].
 +
 +
For example, assumes that we have a class called <code>foo.Users</code>, and we can retrieve a list of users by employing its static method called <code>getAll()</code>. Then, we can implement a variable resolver as follows.
 +
 +
<source lang=" java">
 +
package foo;
 +
public class UserResolver implements org.zkoss.xel.VariableResolver {
 +
    public Object resolveVariable(String name) {
 +
        return "users".equals(name) ? Users.getAll(): null;
 +
    }
 +
}
 +
</source>
 +
 +
And, we can list all users as follows.
 +
 +
<source lang="xml">
 +
<?variable-resolver class="foo.UserResolver"?>
 +
<grid>
 +
    <columns>
 +
        <column label="Name" sort="auto"/>
 +
        <column label="Title" sort="auto"/>
 +
        <column label="Age" sort="auto"/>
 +
    </columns>
 +
    <rows>
 +
        <row forEach="${users}">
 +
            <label value="${each.name}"/>
 +
            <label value="${each.title}"/>
 +
            <label value="${each.age}"/>
 +
        </row>
 +
    </rows>
 +
</grid>
 +
</source>
 +
 +
There are three methods that we can assume <code>foo.User</code>: <code>getName()</code>, <code>getTitle()</code> and <code>getAge()</code>. <code>forEach</code> is used to instantiate components by iterating through a collection of objects.
 +
 +
[[File:DgGettingStartedUsers.png]]
  
 
==MVC: Separate code from user interface==
 
==MVC: Separate code from user interface==
  
Embedding Java code in a ZUML page is straightforward and easy to read. However, in a production environment, it is usually better to separate the code from user interfaces. In addition, the compiled Java code runs much faster than the embedded code which is interpreted at runtime.
+
Embedding Java code in a ZUML page is straightforward and easy for prototyping. However, in a production environment, it is better to separate the code from user interfaces. The code can be compiled at the development time. It is easier to develop and test, and runs much faster than the embedded code which is interpreted at runtime.
  
 
To separate codes from UI, you can implement a Java class (aka., the controller) that implements <javadoc type="interface">org.zkoss.zk.ui.util.Composer</javadoc>, and then handle UI in <javadoc type="interface" method="doAfterCompose(org.zkoss.zk.ui.Component)">org.zkoss.zk.ui.util.Composer</javadoc>. For example, you can redo the previous example by registering an event listener in <javadoc type="interface" method="doAfterCompose(org.zkoss.zk.ui.Component)">org.zkoss.zk.ui.util.Composer</javadoc>, and then retrieve the result by instantiating a label to represent it in the event listener as follows.
 
To separate codes from UI, you can implement a Java class (aka., the controller) that implements <javadoc type="interface">org.zkoss.zk.ui.util.Composer</javadoc>, and then handle UI in <javadoc type="interface" method="doAfterCompose(org.zkoss.zk.ui.Component)">org.zkoss.zk.ui.util.Composer</javadoc>. For example, you can redo the previous example by registering an event listener in <javadoc type="interface" method="doAfterCompose(org.zkoss.zk.ui.Component)">org.zkoss.zk.ui.util.Composer</javadoc>, and then retrieve the result by instantiating a label to represent it in the event listener as follows.
  
<source lang="java">
+
<source lang="java" high="8">
 
package foo;
 
package foo;
 
import org.zkoss.zk.ui.Component;
 
import org.zkoss.zk.ui.Component;
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         target.addEventListener("onClick", new EventListener() { //add a event listener in Java
 
         target.addEventListener("onClick", new EventListener() { //add a event listener in Java
 
             public void onEvent(Event event) {
 
             public void onEvent(Event event) {
                 String prop = System.getProperty(((Textbox)target.getFellow("input")).getValue());
+
                 String prop = System.getProperty(((Textbox)target.query("#input")).getValue());
                 target.getFellow("result").appendChild(new Label(prop));
+
                 target.query("#result").appendChild(new Label(prop));
 
             }
 
             }
 
         });
 
         });
Line 145: Line 185:
 
As shown, an event listener could be registered with the use of <javadoc type="interface" method="addEventListener(java.lang.String, org.zkoss.zk.ui.event.EventListener)">org.zkoss.zk.ui.Component</javadoc>. An event listener must implement <javadoc type="interface">org.zkoss.zk.ui.event.EventListener</javadoc>, and then handle the event in <javadoc type="interface" method="onEvent(org.zkoss.zk.ui.event.Event">org.zkoss.zk.ui.event.EventListener</javadoc>.
 
As shown, an event listener could be registered with the use of <javadoc type="interface" method="addEventListener(java.lang.String, org.zkoss.zk.ui.event.EventListener)">org.zkoss.zk.ui.Component</javadoc>. An event listener must implement <javadoc type="interface">org.zkoss.zk.ui.event.EventListener</javadoc>, and then handle the event in <javadoc type="interface" method="onEvent(org.zkoss.zk.ui.event.Event">org.zkoss.zk.ui.event.EventListener</javadoc>.
  
Also notice that a component assigned with an identifier could be retrieved with the use of <javadoc type="interface" method="getFellow(java.lang.String)" type="interface">org.zkoss.zk.ui.Component</javadoc>.
+
Also notice that a component could be retrieved with the use of <javadoc type="interface" method="query(java.lang.String)" type="interface">org.zkoss.zk.ui.Component</javadoc>, which allows the developer to use a CSS 3 selector to select a component, such as <code>query("#id1 grid textbox")</code>.
  
Then, you could associate the controller (<tt>foo.PropertyRetriever</tt>) with a component using the <tt>apply</tt> attribute as shown below.
+
Then, you could associate the controller (<code>foo.PropertyRetriever</code>) with a component using the <code>apply</code> attribute as shown below.
  
<source lang="xml">
+
<source lang="xml" high="3">
 
<window title="Property Retrieval" border="normal">
 
<window title="Property Retrieval" border="normal">
 
     Enter a property name: <textbox id="input"/>
 
     Enter a property name: <textbox id="input"/>
Line 156: Line 196:
 
</window>
 
</window>
 
</source>
 
</source>
 +
 +
'''For more information, please refer to [http://books.zkoss.org/wiki/ZK_Getting_Started/Get_ZK_Up_and_Running_with_MVC Get ZK Up and Running with MVC ]'''
  
 
==MVC: Autowire UI objects to data members==
 
==MVC: Autowire UI objects to data members==
  
Implementing and registering event listeners is a bit tedious. Thus, ZK provides a feature called autowiring. By extending from <javadoc>org.zkoss.zk.ui.util.GenericForwardComposer</javadoc>, ZK looks for the members if their names match the identifiers of components. For example, you could rewrite <tt>foo.PropertyRetriever</tt> by utilizing the autowriing as follows.
+
Implementing and registering event listeners is a bit tedious. Thus, ZK provides a feature called autowiring. By extending from <javadoc>org.zkoss.zk.ui.select.SelectorComposer</javadoc>, ZK looks for the members annotated with <code>@Wire</code> or <code>@Listen</code> to match the components. For example, you could rewrite <code>foo.PropertyRetriever</code> by utilizing the autowriing as follows.
  
<source lang="java" title="PropertyRetriever.java">
+
<source lang="java" title="PropertyRetriever.java" high="8,9,11,14">
 
package foo;
 
package foo;
 
import org.zkoss.zk.ui.Component;
 
import org.zkoss.zk.ui.Component;
 
import org.zkoss.zk.ui.event.Event;
 
import org.zkoss.zk.ui.event.Event;
import org.zkoss.zk.ui.util.GenericForwardComposer;
+
import org.zkoss.zk.ui.select.SelectorComposer;
 +
import org.zkoss.zk.ui.select.annotation.*;
 
import org.zkoss.zul.*;
 
import org.zkoss.zul.*;
  
public class PropertyRetriever extends GenericForwardComposer {
+
public class PropertyRetriever extends SelectorComposer<Window> {
    Textbox input; // Autowired by same component type/ID
+
@Wire
    Vlayout result; // Autowired by same component type/ID
+
Textbox input; //wired to a component called input
 
+
@Wire
    public void onClick$retrieve(Event event) {
+
Vlayout result; //wired to a component called result
        //handle onClick of the retrieve button
+
        String prop = System.getProperty(input.getValue());
+
@Listen("onClick=#retrieve")
        result.appendChild(new Label(prop));
+
public void submit(Event event) { //register a listener to a component called retrieve
    }
+
String prop = System.getProperty(input.getValue());
 +
result.appendChild(new Label(prop));
 +
}
 
}
 
}
 
</source>
 
</source>
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</source>
 
</source>
  
As shown above, <tt>input</tt> and <tt>result</tt> are automatically assigned such that you could access the real components directly.
+
As shown above, <code>@Wire</code> will cause <code>input</code> and <code>result</code> to be ''wired'' automatically, such that you could access the components directly.
Also <tt>onClick$retrieve</tt> indicates that an event listener will be registered to the component called <tt>retrieve</tt> to handle the <tt>onClick</tt> event.
+
Also <code>@Listen("onClick=#retrieve")</code> indicates that the annotated method will be registered as an event listener to the component called <code>retrieve</code> to handle the <code>onClick</code> event.
 
 
<blockquote style="border:1px solid orange;padding:10px;background-color:#FAF6E3">
 
'''Notice''' : MVC pattern is recommended for a production application. On the other hand, to maintain readability, many examples in our documents embed code directly into ZUML pages.
 
</blockquote>
 
  
==Express data with variable resolver and EL expressions==
+
If the component's ID is different from the member's name or the pattern is complicated, you could specify a CSS 3 selector such as <code>@Wire("#id")</code>, <code>@Wire("window > div > button")</code> and <code>@Listen("onClick = button[label='Clear']")</code>.
  
On a ZUML page, you could locate data with a variable resolver (<javadoc type="interface">org.zkoss.xel.VariableResolver</javadoc>), and then express it with [[ZK Developer's Reference/UI Composing/ZUML/EL Expressions|EL expressions]].
+
You can use with Spring or CDI managed bean in the composer too. For example,
  
For example, assumes that we have a class called <tt>foo.User</tt>, and we can retrieve a list of users by employing its static method called <tt>getAll()</tt>. Then, we can implement a variable resolver as follows.
+
<source lang="java" high="1,3">
 +
@VariableResolver(org.zkoss.zkplus.spring.DelegatingVariableResolver)
 +
public class PasswordSetter extends SelectorComposer<Window> {
 +
    @WireVariable //wire Spring managed bean
 +
    private User user;
 +
    @Wire
 +
    private Textbox password; //wired automatically if there is a textbox named password
  
<source lang=" java">
+
    @Listen("onClick=#submit")
package foo;
+
     public void submit() {
public class UserResolver implements org.zkoss.xel.VariableResolver {
+
         user.setPassword(password.getValue());
     public Object resolveVariable(String name) {
 
         return "users".equals(name) ? Users.getAll(): null;
 
 
     }
 
     }
 
}
 
}
 
</source>
 
</source>
  
And, we can list all users as follows.
+
<blockquote style="border:1px solid orange;padding:10px;background-color:#FAF6E3">
 +
'''Notice''' : MVC pattern is recommended for a production application. On the other hand, to maintain readability, many examples in our documents embed code directly into ZUML pages.
 +
</blockquote>
  
<source lang="xml">
+
==MVVM: Automate the access with data binding==
<?variable-resolver class="foo.UserResolver"?>
 
<grid>
 
    <columns>
 
        <column label="Name" sort="auto"/>
 
        <column label="Title" sort="auto"/>
 
        <column label="Age" sort="auto"/>
 
    </columns>
 
    <rows>
 
        <row forEach="${users}">
 
            <label value="${each.name}"/>
 
            <label value="${each.title}"/>
 
            <label value="${each.age}"/>
 
        </row>
 
    </rows>
 
</grid>
 
</source>
 
  
There are three methods that we can assume <tt>foo.User</tt>: <tt>getName()</tt>, <tt>getTitle()</tt> and <tt>getAge()</tt>. <tt>forEach</tt> is used to instantiate components by iterating through a collection of objects.
+
EL expressions are convenient but they are limited to display read-only data. If you allow end users to modify data (such as CRUD), or change how the data can be displayed based on users' selection, you could use ZK data binding to handle the display and modification automatically for you. All you need to do is to implement a so-called ViewModel (a POJO) that provides the data beans and/or describes relationship between UI and data beans<ref>ZK data binding is based on the MVVM design pattern, which is identical to the [http://martinfowler.com/eaaDev/PresentationModel.html Presentation Model] introduced by Martin Fowler. For more information, please refer to [[ZK Developer's Reference/MVVM|ZK Developer's Reference: MVVM]].</ref>. For example,<ref>Here we load the users by assuming there is a utility called <code>Users</code>. However,  it is straightforward if you'd like to wire Spring-managed or CDI-managed beans. For more information, please refer to [[ZK Developer's Reference/MVC/Controller/Composer|ZK Developer's Reference: MVC]]</ref>.
  
[[File:DgGettingStartedUsers.png]]
+
<source lang="java">
 +
package foo;
 +
public class UserViewModel { 
 +
    List<User> users = Users.getAll();
  
==Automate the access with data binding==
+
    public List<User> getUsers() {
 +
        return users;
 +
    }
 +
}
 +
</source>
  
EL expressions are convenient but they are limited to display read-only data. If you allow end users to modify data or change how the data can be displayed based on users' selection, you could use the data binder to handle the display and modification automatically for us. All you need to do is to provide the model (POJO) with proper getter and setter methods (such as <tt>getName()</tt> and <tt>setName(String)</tt>).
+
Then, you could put them together by applying a built-in composer called <javadoc>org.zkoss.bind.BindComposer</javadoc> in a ZUML document as follows.
  
First, you could declare an initial class <javadoc>org.zkoss.zkplus.databind.AnnotateDataBinderInit</javadoc> and then, express the data (read-only or writable) with annotation expressions<ref>Annotation expressions can be used by another tools, not limited to the data binder.</ref>.
+
<source lang="xml" high="1,2">
The annotation expression is similar to EL expressions, but it starts with <tt>@{</tt>.
+
<grid apply="org.zkoss.bind.BindComposer"
 
+
    viewModel="@id('vm') @init('foo.UserViewModel')" model="@bind(vm.users)">
<source lang="xml">
 
<?init class="org.zkoss.zkplus.databind.AnnotateDataBinderInit"?>
 
<?variable-resolver class="foo.UserResolver"?>
 
<grid model="@{users}">
 
 
     <columns>
 
     <columns>
         <column label="Name" sort="auto"/>
+
         <column label="Name" sort="auto" />
         <column label="Title" sort="auto"/>
+
         <column label="Title" sort="auto" />
         <column label="Age" sort="auto"/>
+
         <column label="Age" sort="auto" />
 
     </columns>
 
     </columns>
     <rows>
+
     <template name="model" var="user">
         <row self="@{each='user'}">
+
         <row>
             <textbox value="@{user.name}"/>
+
             <textbox value="@bind(user.name)" />
             <textbox value="@{user.title}"/>
+
             <textbox value="@bind(user.title)" />
             <intbox value="@{user.age}"/>
+
             <intbox value="@bind(user.age)" />
 
         </row>
 
         </row>
     </rows>
+
     </template>
 
</grid>
 
</grid>
 
</source>
 
</source>
  
where a special annotation expression, <tt>self="@{each='user'}"</tt>, is used to iterate through a collection of users.
+
[[File:DgGettingStartedUsers2.png]]
  
[[File:DgGettingStartedUsers2.png]]
+
Please notice that you do not need to write any code to handle the display or modification. Rather, you declare the relation of the UI and data beans in [[ZK Developer's Reference/Annotations|annotations]], such as <code>@bind(user.name)</code>. Any modification made to each input (by the end user) is stored back to the object (<code>foo.User</code>) automatically and vice versa, assuming that the POJO has the required setter methods, such as <code>setName(String)</code>.
  
Please notice that developers do not need to handle the display or modification. They only need to prepare a POJO (such as <tt>foo.User</tt>). Any modification made to each input (by the end user) is stored back to the object (<tt>foo.User</tt>) automatically, assuming that the POJO has the required setter methods, such as <tt>setName(String)</tt>.
+
'''For more information, please refer to [http://books.zkoss.org/wiki/ZK_Getting_Started/Get_ZK_Up_and_Running_with_MVC Get ZK Up and Running with MVVM]'''
  
 
<blockquote>
 
<blockquote>
 
----
 
----
 
<references/>
 
<references/>
 +
</blockquote>
 +
 +
<blockquote style="border:1px solid orange;padding:10px;background-color:#FAF6E3">
 +
'''Notice''' :
 +
MVVM pattern applies to ZK 6 and later
 
</blockquote>
 
</blockquote>
  

Latest revision as of 07:34, 14 January 2022

This tutorial guides you through the most fundamental features and concepts of ZK.

Hello World!

After ZK is installed on your favorite Web server[1], writing applications is straightforward. Just create a ZUML file[2], and name it as hello.zul[3], under one of the Web application's directories just as you would do for an HTML file.

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


Assuming the name of the Web project is myapp, then go to the corresponding URL, which is http://localhost/myapp/hello.zul, and you'll see your first ZK application running.

DgGettingStartedHello.zul.png

On a ZUML page, an XML element describes what a component[4] can create while the XML attributes are used to assign values to a component's properties. In this example, a window component is created and its title is set to "My First ZK Application" and its border is set to normal.

The text enclosed in the XML elements can also be interpreted as a special component called label. Thus, the above example is equivalent to the following code:

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

  1. Please refer to ZK Installation Guide.
  2. ZUML [1]
  3. The other way to try examples is to use ZK Sandbox to run them.
  4. Interface : <javadoc type="interface">org.zkoss.zk.ui.Component

Say Hello in Ajax way

Let us put some interactivity into it.

 <button label="Say Hello" onClick='Messagebox.show("Hello World!")'/>

Then, when you click the button, you'll see the following:

DgGettingStartedHello2.png

The onClick attribute is a special attribute used to add an event listener(EventListener) to the component such as that it is invoked when an end user clicks the component. The attribute value could be any legal Java code. Notice that it is NOT JavaScript, and you have to use double quotes (") in a string. To escape a double quote in an XML string, you could use single quotes (') to enclose it[1].


Here we invoke Messagebox.show(String) to display a message box shown above.

The Java code is interpreted by BeanShell at runtime. In addition to event handling, you could embed the code in a ZUML page by specifying it in a special element called zscript. For example, you could simply define a function in the code as the following:

 <window title="My First ZK Application" border="normal">
 	<button label="Say Hello" onClick='alert("Hello World!")'/>
 	<zscript>
 		void alert(String message){ //declare a function
 			Messagebox.show(message);
 		}
 	</zscript>
 </window>

In fact, alert is a built-in function that you can use directly from the embedded Java code.


  1. If you are not familiar with XML, you might take a look at the XML background section.

It is Java that runs on the server

The embedded Java code runs on the server so as to gain easy access to any resources available on the server. For example,

<window title="Property Retrieval" border="normal">
    Enter a property name: <textbox/>
    <button label="Retrieve" onClick="alert(System.getProperty(self.getPreviousSibling().getValue()))"/>
</window>

where self is a built-in variable which refers a component receiving the event.

If you enter java.version and then click the button, the result will be shown as the following:

DgGettingStartedProperty.png

A component is a POJO

A component is a POJO. You could instantiate and manipulate them directly. For example, you could generate the result by instantiating component(s) to represent it, and then append them to another component as shown below.

<window title="Property Retrieval" border="normal">
    Enter a property name: <textbox id="input"/>
    <button label="Retrieve"
     onClick="result.appendChild(new Label(System.getProperty(input.getValue())))"/>
    <vlayout id="result"/>
</window>

Once appended, the components can be displayed in the browser automatically. Similarly, if components are detached, they are removed from the browser automatically.

In addition, you could change the state of a component directly. All modifications will be synchronized back to the browser automatically.

<window title="Property Retrieval" border="normal">
    Enter a property name: <textbox id="input"/>
    <button label="Retrieve"
     onClick="result.setValue(System.getProperty(input.getValue()))"/>
    <separator/>
    <label id="result"/>
</window>

A component is a LEGO brick

Instead of introducing different components for different purposes, our components are designed to build blocks. You are free to compose blocks together to realize sophisticated UI without customizing any components. For example, you could put anything in a grid, including grid itself; anything in any layout, including the layout itself. Please see our demo for more examples.

Express data with variable resolver and EL expressions

On a ZUML page, you could locate data with a variable resolver (VariableResolver), and then express it with EL expressions.

For example, assumes that we have a class called foo.Users, and we can retrieve a list of users by employing its static method called getAll(). Then, we can implement a variable resolver as follows.

package foo;
public class UserResolver implements org.zkoss.xel.VariableResolver {
    public Object resolveVariable(String name) {
        return "users".equals(name) ? Users.getAll(): null;
    }
}

And, we can list all users as follows.

<?variable-resolver class="foo.UserResolver"?>
<grid>
    <columns>
        <column label="Name" sort="auto"/>
        <column label="Title" sort="auto"/>
        <column label="Age" sort="auto"/>
    </columns>
    <rows>
        <row forEach="${users}">
            <label value="${each.name}"/>
            <label value="${each.title}"/>
            <label value="${each.age}"/>
        </row>
    </rows>
</grid>

There are three methods that we can assume foo.User: getName(), getTitle() and getAge(). forEach is used to instantiate components by iterating through a collection of objects.

DgGettingStartedUsers.png

MVC: Separate code from user interface

Embedding Java code in a ZUML page is straightforward and easy for prototyping. However, in a production environment, it is better to separate the code from user interfaces. The code can be compiled at the development time. It is easier to develop and test, and runs much faster than the embedded code which is interpreted at runtime.

To separate codes from UI, you can implement a Java class (aka., the controller) that implements Composer, and then handle UI in Composer.doAfterCompose(Component). For example, you can redo the previous example by registering an event listener in Composer.doAfterCompose(Component), and then retrieve the result by instantiating a label to represent it in the event listener as follows.

package foo;
import org.zkoss.zk.ui.Component;
import org.zkoss.zk.ui.util.Composer;
import org.zkoss.zk.ui.event.EventListener;
import org.zkoss.zul.Label;

public class PropertyRetriever implements Composer {
    public void doAfterCompose(final Component target) { //handle UI here
        target.addEventListener("onClick", new EventListener() { //add a event listener in Java
            public void onEvent(Event event) {
                String prop = System.getProperty(((Textbox)target.query("#input")).getValue());
                target.query("#result").appendChild(new Label(prop));
            }
        });
    }
}

As shown, an event listener could be registered with the use of Component.addEventListener(String, EventListener). An event listener must implement EventListener, and then handle the event in EventListener.onEvent(org.zkoss.zk.ui.event.Event.

Also notice that a component could be retrieved with the use of Component.query(String), which allows the developer to use a CSS 3 selector to select a component, such as query("#id1 grid textbox").

Then, you could associate the controller (foo.PropertyRetriever) with a component using the apply attribute as shown below.

<window title="Property Retrieval" border="normal">
    Enter a property name: <textbox id="input"/>
    <button label="Retrieve" apply="foo.PropertyRetriever"/>
    <vlayout id="result"/>
</window>

For more information, please refer to Get ZK Up and Running with MVC

MVC: Autowire UI objects to data members

Implementing and registering event listeners is a bit tedious. Thus, ZK provides a feature called autowiring. By extending from SelectorComposer, ZK looks for the members annotated with @Wire or @Listen to match the components. For example, you could rewrite foo.PropertyRetriever by utilizing the autowriing as follows.

package foo;
import org.zkoss.zk.ui.Component;
import org.zkoss.zk.ui.event.Event;
import org.zkoss.zk.ui.select.SelectorComposer;
import org.zkoss.zk.ui.select.annotation.*;
import org.zkoss.zul.*;

public class PropertyRetriever extends SelectorComposer<Window> {
	@Wire
	Textbox input; //wired to a component called input
	@Wire
	Vlayout result; //wired to a component called result
	
	@Listen("onClick=#retrieve")
	public void submit(Event event) { //register a listener to a component called retrieve
		String prop = System.getProperty(input.getValue());
		result.appendChild(new Label(prop));
	}
}

and the ZUL page is as follows.

<window title="Property Retrieval" border="normal" apply="foo.PropertyRetriever">
    Enter a property name: <textbox id="input"/>
    <button label="Retrieve" id="retrieve"/>
    <vlayout id="result"/>
</window>

As shown above, @Wire will cause input and result to be wired automatically, such that you could access the components directly. Also @Listen("onClick=#retrieve") indicates that the annotated method will be registered as an event listener to the component called retrieve to handle the onClick event.

If the component's ID is different from the member's name or the pattern is complicated, you could specify a CSS 3 selector such as @Wire("#id"), @Wire("window > div > button") and @Listen("onClick = button[label='Clear']").

You can use with Spring or CDI managed bean in the composer too. For example,

@VariableResolver(org.zkoss.zkplus.spring.DelegatingVariableResolver)
public class PasswordSetter extends SelectorComposer<Window> {
    @WireVariable //wire Spring managed bean
    private User user;
    @Wire
    private Textbox password; //wired automatically if there is a textbox named password

    @Listen("onClick=#submit")
    public void submit() {
        user.setPassword(password.getValue());
    }
}

Notice : MVC pattern is recommended for a production application. On the other hand, to maintain readability, many examples in our documents embed code directly into ZUML pages.

MVVM: Automate the access with data binding

EL expressions are convenient but they are limited to display read-only data. If you allow end users to modify data (such as CRUD), or change how the data can be displayed based on users' selection, you could use ZK data binding to handle the display and modification automatically for you. All you need to do is to implement a so-called ViewModel (a POJO) that provides the data beans and/or describes relationship between UI and data beans[1]. For example,[2].

package foo;
public class UserViewModel {   
    List<User> users = Users.getAll();

    public List<User> getUsers() {
        return users;
    }
}

Then, you could put them together by applying a built-in composer called BindComposer in a ZUML document as follows.

<grid apply="org.zkoss.bind.BindComposer"
    viewModel="@id('vm') @init('foo.UserViewModel')" model="@bind(vm.users)">
    <columns>
        <column label="Name" sort="auto" />
        <column label="Title" sort="auto" />
        <column label="Age" sort="auto" />
    </columns>
    <template name="model" var="user">
        <row>
            <textbox value="@bind(user.name)" />
            <textbox value="@bind(user.title)" />
            <intbox value="@bind(user.age)" />
        </row>
    </template>
</grid>

DgGettingStartedUsers2.png

Please notice that you do not need to write any code to handle the display or modification. Rather, you declare the relation of the UI and data beans in annotations, such as @bind(user.name). Any modification made to each input (by the end user) is stored back to the object (foo.User) automatically and vice versa, assuming that the POJO has the required setter methods, such as setName(String).

For more information, please refer to Get ZK Up and Running with MVVM


  1. ZK data binding is based on the MVVM design pattern, which is identical to the Presentation Model introduced by Martin Fowler. For more information, please refer to ZK Developer's Reference: MVVM.
  2. Here we load the users by assuming there is a utility called Users. However, it is straightforward if you'd like to wire Spring-managed or CDI-managed beans. For more information, please refer to ZK Developer's Reference: MVC

Notice : MVVM pattern applies to ZK 6 and later

Define UI in pure Java

In additions to XML, developers could also define UI in pure Java. For example, you could implement the property-retrieval example as follows.

public class PropertyRetrieval extends GenericRichlet {
	public void service(Page page) throws Exception {
		final Window main = new Window("Property Retrieval", "normal", false);
		main.appendChild(new Label("Enter a property name: "));

		final Textbox input = new Textbox();
		input.setId("input");
		main.appendChild(input);

		final Button button = new Button("Retrieve");
		button.addEventListener("onClick",
			new EventListener() {
				public void onEvent(Event event) throws Exception {
					Messagebox.show(System.getProperty(input.getValue()));
				}
			});
		main.appendChild(button);

		main.setPage(page); //attach so it and all descendants will be generated to the client
	}
}

A richlet (Richlet) is a small Java program that creates all necessary user interfaces for a given page in response to users' request. Here we extend java.lang.Object from a skeleton called GenericRichlet. Then, we create all the required components in Richlet.service(Page).

Adding client-side functionality

In addition to handling events and components on the server, ZK also provides an option allowing developers to control UI from the client side. We have dubbed this blending of technology, Server+client Fusion.

For example, we could re-implement the Hello World example with the code from the client side as follows.

<button label="Say Hello" w:onClick='jq.alert("Hello World!")' xmlns:w="client"/>

where we declare a XML namespace named client to indicate the event handler which will be evaluated at the client side. In addition, jq.alert(String, Map) is a client-side method equivalent to Messagebox.show(String).

All components are available and accessible to the client. For example, here is a number guessing game that manipulates UI from the client side.

<window title="Guess a number" border="normal">
	<vlayout>
    Type number between 0 and 99 and then press Enter to guess:
    <intbox w:onOK="guess(this)" xmlns:w="client"/>
    </vlayout>
    <script><![CDATA[
	var num = Math.floor(Math.random() * 100);
	function guess(wgt) {
		var val = wgt.getValue(),
			mesg = val > num ? "smaller than " + val:
				val < num ? "larger than "+val: val + " is correct!";
		wgt.parent.appendChild(new zul.wgt.Label({value: mesg}));
		wgt.setValue("");
	}
    ]]></script>
</window>

where onOK is an event fired when the user presses Enter, and script is used to embed the client-side code (in contrast to zscript for embedding the server-side code).

DgGettingStartedGuessNumber.png

Architecture overview

Architecture-s.png

When a ZK application runs on the server, it gives access to backend resources, assemble UI with components, listen to users' activity, and then manipulate components to update UI. All are done on the server. The synchronization of the states of the components between the browser and the server is done automatically by ZK and transparently to the application.

When running on the server, the application can access full Java technology stack. Users' activities, including Ajax and Server Push, are abstracted to event objects. UI are composed of POJO-like components. It is the most productive approach to develop a modern Web application.

With ZK's Server+client Fusion architecture, your application will never stop running on the server. You can enhance your application's interactivity by adding optional client-side functionality, such as client-side event handling, visual effect customizing and even UI composing without server-side coding. ZK is the only framework to enable seamless fusion from pure server-centric to pure client-centric. You can have the best of two worlds: productivity and flexibility.


Last Update : 2022/01/14