Richlet"

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A richlet must implement the <javadoc type="interface">org.zkoss.zk.ui.Richlet</javadoc> interface. However, you generally do not have to implement it from scratch. Rather, you could extend <javadoc>org.zkoss.zk.ui.GenericRichlet</javadoc>, and the only thing you have to do is to override <javadoc method="service(org.zkoss.zk.ui.Page)">org.zkoss.zk.ui.Richlet</javadoc>. The method is called when an associated URL is requested. For example,
 
A richlet must implement the <javadoc type="interface">org.zkoss.zk.ui.Richlet</javadoc> interface. However, you generally do not have to implement it from scratch. Rather, you could extend <javadoc>org.zkoss.zk.ui.GenericRichlet</javadoc>, and the only thing you have to do is to override <javadoc method="service(org.zkoss.zk.ui.Page)">org.zkoss.zk.ui.Richlet</javadoc>. The method is called when an associated URL is requested. For example,
  
<source lang="java" high="27, 31, 37">
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<source lang="java" highlight="27, 31, 37">
 
  package org.zkoss.reference.developer.uicomposing;
 
  package org.zkoss.reference.developer.uicomposing;
  
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</source>
 
</source>
  
In Richlet, you have to compose UI by your own, but some components only support specific child components. We recommend you to read [[ZK Component Reference]] before you start to build.
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In Richlet, you have to compose UI on your own, but some components only support specific child components. We recommend you to read [[ZK Component Reference]] before you start to build.
  
 
As shown above (line 27), we have to invoke <javadoc method="setPage(Page page)">org.zkoss.zk.ui.Component</javadoc> explicitly to attach a root component to a page so it will be available at the client.
 
As shown above (line 27), we have to invoke <javadoc method="setPage(Page page)">org.zkoss.zk.ui.Component</javadoc> explicitly to attach a root component to a page so it will be available at the client.
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== Richlet Must Be Thread-Safe ==
 
== Richlet Must Be Thread-Safe ==
  
Like a servlet, a single instance of richlet is created and shared with all users for all requests for the mapped URL. A richlet must handle the concurrent requests, and be careful to synchronize access to shared resources. In other words, a richlet (the implementation of the <tt>service</tt> method) must be thread-safe.
+
Like a servlet, a single instance of richlet is created and shared with all users for all requests for the mapped URL. A richlet must handle the concurrent requests, and be careful to synchronize access to shared resources. In other words, a richlet (the implementation of the <code>service</code> method) must be thread-safe.
  
 
== Don't Share Components ==
 
== Don't Share Components ==
  
When a request (not Ajax request but regular HTTP request) is made by an user, a <javadoc>org.zkoss.zk.ui.Desktop</javadoc> and a <javadoc>org.zkoss.zk.ui.Page</javadoc> are created first, and then <javadoc method="service(org.zkoss.zk.ui.Page)">org.zkoss.zk.ui.Richlet</javadoc> is invoked to serve the request<ref>A normal HTTP request; not an Ajax request. Ajax requests are handled in the same way as ZUML. For more information please refer to the [[ZK Developer's Reference/Event Handling|Event Handling]] section</ref>. In other words, each request is served with an individual desktop and page. Therefore, we ''cannot'' share components among different invocation of <javadoc method="service(org.zkoss.zk.ui.Page)">org.zkoss.zk.ui.Richlet</javadoc>.
+
When a request (not Ajax request but regular HTTP request) is made by a user, a <javadoc>org.zkoss.zk.ui.Desktop</javadoc> and a <javadoc>org.zkoss.zk.ui.Page</javadoc> are created first, and then <javadoc method="service(org.zkoss.zk.ui.Page)">org.zkoss.zk.ui.Richlet</javadoc> is invoked to serve the request<ref>A normal HTTP request; not an Ajax request. Ajax requests are handled in the same way as ZUML. For more information please refer to the [[ZK Developer's Reference/Event Handling|Event Handling]] section</ref>. In other words, each request is served with an individual desktop and page. Therefore, we ''cannot'' share components among different invocations of <javadoc method="service(org.zkoss.zk.ui.Page)">org.zkoss.zk.ui.Richlet</javadoc>.
  
 
For example, the following code is illegal:
 
For example, the following code is illegal:
  
<source lang="java" high=7">
+
<source lang="java" highlight=7">
 
public class MyRichlet extends GenericRichlet {
 
public class MyRichlet extends GenericRichlet {
 
     private Window main; //Not a good idea to share
 
     private Window main; //Not a good idea to share
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</source>
 
</source>
  
Why?  Each deskop should have its own set of component instances<ref>For more information, please refer to [[ZK_Developer's Reference/UI Composing/Component-based UI|Component-based UI]] section</ref>. When the URL associated '''MyRichlet''' is requested a second time, an exception will be thrown because the '''main''' window is already instantiated and associated with the first desktop created from the first request. We cannot assign it to the second desktop.
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Why?  Each desktop should have its own set of component instances<ref>For more information, please refer to [[ZK_Developer's Reference/UI Composing/Component-based UI|Component-based UI]] section</ref>. When the URL associated '''MyRichlet''' is requested a second time, an exception will be thrown because the '''main''' window is already instantiated and associated with the first desktop created from the first request. We cannot assign it to the second desktop.
  
 
<blockquote>
 
<blockquote>
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==Turn on Richlet==
 
==Turn on Richlet==
By default, richlets are disabled. To enable them, please add the following declaration to <tt>WEB-INF/web.xml</tt>. Once enabled, you can add as many as richlets as you want without modifying <tt>web.xml</tt>.
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By default, richlets are disabled. To enable them, please add the following declaration to <code>WEB-INF/web.xml</code>. Once enabled, you can add as many richlets as you want without modifying <code>web.xml</code>.
  
 
With servlet-mapping:
 
With servlet-mapping:
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</source>
 
</source>
  
Since ZK 7.0.0, you can use Richlet Filter instead.
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{{versionSince| 7.0.0}} You can use <code>RichletFilter</code> instead.
<source lang="xml" high="3,8">
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<source lang="xml" highlight="3,8">
 
<filter>
 
<filter>
 
<filter-name>RichletFilter</filter-name>
 
<filter-name>RichletFilter</filter-name>
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</source>
 
</source>
  
where you can replace <code>/zk/*</code> to any pattern you like, such as <code>/do/*</code>. Notice that you ''cannot'' map it to an extension (such as <code>*.do</code>) since it will be considered as a ZUML page (rather than a richlet).
+
where you can replace <code>/zk/*</code> with any pattern you like, such as <code>/do/*</code>. Notice that you ''cannot'' map it to an extension (such as <code>*.do</code>) since it will be considered as a ZUML page (rather than a richlet).
  
 
==Map URL pattern to Richlet==
 
==Map URL pattern to Richlet==
For each richlet you implement, you can define it in <tt>WEB-INF/zk.xml</tt> with the statement similar to the following:
+
For each richlet you implement, you can define it in <code>WEB-INF/zk.xml</code> with the statement similar to the following:
  
 
<source lang="xml" >
 
<source lang="xml" >
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</source>
 
</source>
  
After defining a richlet, you can map it to any number of URLs using the <tt>richlet-mapping</tt> element as shown below.
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After defining a richlet, you can map it to any number of URLs using the <code>richlet-mapping</code> element as shown below.
  
 
<source lang="xml" >
 
<source lang="xml" >
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'''Note:''' With Richlet Filter (since ZK 7.0.0), you should add the prefix of url-pattern of the filter-mapping into the url-pattern of richlet-mapping.
 
'''Note:''' With Richlet Filter (since ZK 7.0.0), you should add the prefix of url-pattern of the filter-mapping into the url-pattern of richlet-mapping.
 
For example,
 
For example,
<source lang="xml" high="7">
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<source lang="xml" highlight="7">
 
<richlet-mapping>
 
<richlet-mapping>
 
     <richlet-name>Test</richlet-name>
 
     <richlet-name>Test</richlet-name>
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</richlet-mapping>
 
</richlet-mapping>
 
</source>
 
</source>
As you can see the highlight above, the '''/zk''' is added which is according to the filter-mapping.
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As you can see in the highlight above, the '''/zk''' is added which is according to the filter-mapping.
  
  
 
Then, you can visit [http://localhost:8080/PROJECT_NAME/zk/test http://localhost:8080/PROJECT_NAME/zk/test] to request the richlet.
 
Then, you can visit [http://localhost:8080/PROJECT_NAME/zk/test http://localhost:8080/PROJECT_NAME/zk/test] to request the richlet.
  
The URL specified in the <tt>url-pattern</tt> element must start with <tt>/</tt>. If the URI ends with <tt>/*</tt>, it is matched to all request with the same prefix. To retrieve the request's actual URL, you can check the value returned by the <tt>getRequestPath</tt> method of the current page.
+
The URL specified in the <code>url-pattern</code> element must start with <code>/</code>. If the URI ends with <code>/*</code>, it is matched to all requests with the same prefix. To retrieve the request's actual URL, you can check the value returned by the <code>getRequestPath</code> method of the current page.
  
 
<source lang="java" >
 
<source lang="java" >
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<blockquote>
 
<blockquote>
 
----  
 
----  
'''Tip''': By specifying <tt>/*</tt> as the <tt>url-pattern</tt>, you can map all unmatched URLs to your richlet.
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'''Tip''': By specifying <code>/*</code> as the <code>url-pattern</code>, you can map all unmatched URLs to your richlet.
 
</blockquote>
 
</blockquote>
  
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</source>
 
</source>
  
=Version History=
+
 
{{LastUpdated}}
 
{| border='1px' | width="100%"
 
! Version !! Date !! Content
 
|-
 
| &nbsp;
 
| &nbsp;
 
| &nbsp;
 
|}
 
  
 
{{ZKDevelopersReferencePageFooter}}
 
{{ZKDevelopersReferencePageFooter}}

Latest revision as of 05:53, 6 February 2024

Overview

A richlet is a small Java program that composes a user interface in Java for serving the user's request. Before composing UI in Java, we suggest you to know basic concept: UI Composing/Component-based UI first.

When a user requests the content of an URL, ZK Loader checks if the resource of the specified URL is a ZUML page or a richlet. If it is a ZUML page, ZK Loader will create components automatically based on the ZUML page's content as we described in the previous chapters.

If the resource is a richlet, ZK Loader hands over the processing to the richlet. What and how to create components are all handled by the richlet. In other words, it is the developer's job to create all the necessary components programmatically in response to the request.

The choice between the ZUML pages and richlets depends on your preference. However, the performance should not cause any concern since parsing ZUML is optimized.

Implement a Richlet

It is straightforward to implement a richlet. First, you have to implement the Richlet interface before mapping a URL to the richlet.

Implement a Richlet as a Java class

A richlet must implement the Richlet interface. However, you generally do not have to implement it from scratch. Rather, you could extend GenericRichlet, and the only thing you have to do is to override Richlet.service(Page). The method is called when an associated URL is requested. For example,

 package org.zkoss.reference.developer.uicomposing;

import org.zkoss.zk.ui.*;
import org.zkoss.zk.ui.event.*;
import org.zkoss.zul.*;

public class TestRichlet extends GenericRichlet {
	//Richlet//
	public void service(Page page) {
		page.setTitle("Richlet Test");

		final Window w = new Window("Richlet Test", "normal", false);
		new Label("Hello World!").setParent(w);
		final Label l = new Label();
		l.setParent(w);

		final Button b = new Button("Change");
		b.addEventListener(Events.ON_CLICK,
				new EventListener() {
			int count;
			public void onEvent(Event evt) {
				l.setValue("" + ++count);
			}
		});
		b.setParent(w);

		w.setPage(page);
	}

	@Override
	public void init(RichletConfig config) {
		super.init(config);
		//initialize resources
	}

	@Override
	public void destroy() {
		super.destroy();
		//destroy resources
	}
}

In Richlet, you have to compose UI on your own, but some components only support specific child components. We recommend you to read ZK Component Reference before you start to build.

As shown above (line 27), we have to invoke Component.setPage(Page page) explicitly to attach a root component to a page so it will be available at the client.

To have better control, you can even implement the Richlet.init(RichletConfig) and Richlet.destroy() methods to initialize and to destroy any resources required by the richlet when it is loaded.

In addition, you could implement Richlet.getLanguageDefinition() to use a different language as default (for example, implementing a richlet for mobile devices). By default, ZUL (aka., xul/html) is assumed.

Richlet Must Be Thread-Safe

Like a servlet, a single instance of richlet is created and shared with all users for all requests for the mapped URL. A richlet must handle the concurrent requests, and be careful to synchronize access to shared resources. In other words, a richlet (the implementation of the service method) must be thread-safe.

Don't Share Components

When a request (not Ajax request but regular HTTP request) is made by a user, a Desktop and a Page are created first, and then Richlet.service(Page) is invoked to serve the request[1]. In other words, each request is served with an individual desktop and page. Therefore, we cannot share components among different invocations of Richlet.service(Page).

For example, the following code is illegal:

public class MyRichlet extends GenericRichlet {
    private Window main; //Not a good idea to share
    public void service(Page page) {
        if (main == null) {
            main = new Window();
        }
        main.setPage(main); //ERROR! Causes an exception if the same URL is requested twice!
...

Why? Each desktop should have its own set of component instances[2]. When the URL associated MyRichlet is requested a second time, an exception will be thrown because the main window is already instantiated and associated with the first desktop created from the first request. We cannot assign it to the second desktop.


  1. A normal HTTP request; not an Ajax request. Ajax requests are handled in the same way as ZUML. For more information please refer to the Event Handling section
  2. For more information, please refer to Component-based UI section

Map URL to a Richlet

To map URL to a richlet, there are two steps.

  1. Turn on the support of Richlet (in WEB-INF/web.xml)
  2. Map URL pattern to Richlet (in WEB-INF/zk.xml)

Turn on Richlet

By default, richlets are disabled. To enable them, please add the following declaration to WEB-INF/web.xml. Once enabled, you can add as many richlets as you want without modifying web.xml.

With servlet-mapping:

<servlet-mapping>
    <servlet-name>zkLoader</servlet-name>
    <url-pattern>/zk/*</url-pattern>
</servlet-mapping>

Since 7.0.0 You can use RichletFilter instead.

<filter>
	<filter-name>RichletFilter</filter-name>
	<filter-class>org.zkoss.zk.ui.http.RichletFilter</filter-class>
</filter>

<filter-mapping>
	<filter-name>RichletFilter</filter-name>
	<url-pattern>/zk/*</url-pattern>
</filter-mapping>

where you can replace /zk/* with any pattern you like, such as /do/*. Notice that you cannot map it to an extension (such as *.do) since it will be considered as a ZUML page (rather than a richlet).

Map URL pattern to Richlet

For each richlet you implement, you can define it in WEB-INF/zk.xml with the statement similar to the following:

<richlet>
    <richlet-name>Test</richlet-name><!-- your preferred name -->
    <richlet-class>org.zkoss.zkdemo.TestRichlet</richlet-class><!-- your class name, of course -->
</richlet>

After defining a richlet, you can map it to any number of URLs using the richlet-mapping element as shown below.

<richlet-mapping>
    <richlet-name>Test</richlet-name>
    <url-pattern>/test</url-pattern>
</richlet-mapping>
<richlet-mapping>
    <richlet-name>Test</richlet-name>
    <url-pattern>/some/more/*</url-pattern>
</richlet-mapping>

Note: With Richlet Filter (since ZK 7.0.0), you should add the prefix of url-pattern of the filter-mapping into the url-pattern of richlet-mapping. For example,

<richlet-mapping>
    <richlet-name>Test</richlet-name>
    <url-pattern>/test</url-pattern>
</richlet-mapping>
<richlet-mapping>
    <richlet-name>Test</richlet-name>
    <url-pattern>/zk/some/more/*</url-pattern>
</richlet-mapping>

As you can see in the highlight above, the /zk is added which is according to the filter-mapping.


Then, you can visit http://localhost:8080/PROJECT_NAME/zk/test to request the richlet.

The URL specified in the url-pattern element must start with /. If the URI ends with /*, it is matched to all requests with the same prefix. To retrieve the request's actual URL, you can check the value returned by the getRequestPath method of the current page.

 public void service(Page page) {
     if ("/some/more/hi".equals(page.getRequestPath()) {
         ...
     }
 }

Tip: By specifying /* as the url-pattern, you can map all unmatched URLs to your richlet.

Load ZUML in Richlet

Execution provides a collection of methods, such as Execution.createComponents(String, Component, Map), allowing developers to load ZUML documents dynamically. You could load a ZUML document from any source you like, such as database. Please refer to the Load ZUML in Java for details.

Use Spring in Richlet

To use Spring-managed beans in richlets you need the context loader listener that creates spring application context as described in ZK Spring Essentials/Getting Started with ZK Spring/Setting Up ZK Spring. Then you could load Spring beans by using a utility class SpringUtil:

    Object bean = SpringUtil.getBean(beanName);




Last Update : 2024/02/06

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