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You could assign a label and an image to a button by the label and image properties. If both are specified, the dir property control which is displayed up front, and the orient property controls whether the layout is horizontal or vertical.

Within ZK 5, the file upload has been redesigned so it can be integrated with any widget. For example, the button now can be used to upload a file. In addition to this, the display of the upload status has been enhanced and can be customized easily.


ZKComRef Button.jpg

	<button label="Left" image="/img/network.gif" width="125px"/>
	<button label="Right" image="/img/network.gif" dir="reverse" width="125px"/>
	<button label="Above" image="/img/network.gif" orient="vertical" width="125px"/>
	<button label="Below" image="/img/network.gif" orient="vertical" dir="reverse" width="125px"/>

In addition to employing URLs to specify images, you can dynamically assign a generated image to a button using the setImageContent method. Refer to the following section for details.

Tip: The setImageContent method is supplied by all components that have an image property. Simply put, setImageContent is used for dynamically generated images, while image is used for images identifiable by a URL.

File Upload

Any button[1] can be used to upload files. All you need to do is:

  1. Specify the upload attribute with true
  2. Handles the onUpload event.
<button upload="true" label="Fileupload" onUpload="myProcessUpload(event.getMedia())"/>

When the file is uploaded, an instance of UploadEvent is sent to the button. Then, the event listener can retrieve the uploaded content by examining the return value of UploadEvent.getMedia().

  1. Any Toolbarbutton can be used to upload files too.

Custom Error Message When Fileupload Over Maxsize

1. Write your own AuLoader

package test;  

import org.apache.commons.fileupload.FileUploadBase.SizeLimitExceededException; 

public class MyUploader extends AuUploader { 	

   protected String handleError(Throwable ex) { 		 		
      if(ex instanceof SizeLimitExceededException){ 			
         SizeLimitExceededException e = (SizeLimitExceededException) ex; 			
         return e.getActualSize() + " is over our limit"; 		
      return super.handleError(ex); 	

2. Apply it in the web.xml

   <description>The asynchronous update engine for ZK</description> 	

Limitation of the Default Mold

The default mold of a button uses HTML BUTTON tag to represent it visually. It is efficient, but it has some limitations:

  1. The look might be different from one browser to another.
  2. It doesn't support the file upload. In fact, it will become the trendy mold automatically if upload is specified.
  3. If it is disabled it can not receive mouse events and hence can not use ZK popup component as tooltip.

If it is an issue, you could use the trendy mold instead.

<button label="OK" mold="trendy"/>

Configure to Use the Trendy Mold as Default

If you prefer to use the trendy mold as default, you could configure ZK by adding the following to /WEB-INF/zk.xml




Button.setAutodisable(String) is used to disable a button automatically, when it is clicked. It is useful to prevent the user from clicking it twice (and firing redundant requests), which is common if the request takes long to serve.

The simplest use is to specify it with self as follows. Then, the button is disabled when it is clicked.

<button id="ok" label="OK" autodisable="self" />

If you'd like to disable several buttons, you could specify all of them in this property by separating with a comma. For example, the following disables both buttons, when one of them is clicked.

<button id="ok" label="OK" autodisable="ok,cancel" />
<button id="cancel" label="Cancel" autodisable="ok,cancel" />

The button will be enabled automatically, after the request has been served (i.e., the response has been sent back to the client). If you prefer to enable them manually (i.e., by calling Button.setDisabled(boolean) explicitly), you could prefix the ID with a plus (+). For example,

<button id="ok" label="OK" autodisable="+self, +cancel" />

Then, you could enable them manually under the situation depending on your application's requirement, such as

if (something_happens) {

Enable Autodisable for All Buttons

As described in ZK Developer's Reference: Customization, you could customize ZK to enable autodisable for all button by specifying the following in the custom language addon:



In addition to handling the onClick event, you could specify the URL in the href property (Button.setHref(String)), such that the browser will navigate to the URL you specified directly (without sending back any request to the server). If you prefer to visit the URL in another browser window, you could specify the name in Button.setTarget(String) (just like using a HTML A tag).

Notice that the end user could hold the Control key and click on the button to visit the link in a new browser window (like a HTML A tag does).

Href and the onClick Event

There are two ways to add behavior to a button and toolbarbutton. Firstly, you can specify a listener to the onClick event. Secondly, you could specify a URL for the href property (Button.setHref(String)). If both are specified, the href property has the higher priority, i.e., the onClick event won't be sent.

	<window title="example">
		<button label="click me" onClick="do_something_in_Java()"/>
		<button label="don't click that one, click me" href="/another_page.zul"/>

Href and SendRedirect

The href property is processed at the client. In other words, the browser will jump to the URL specified in the href property, so your application running at the server has no chance to process it.

If you have to process it at the server or you have to decide whether to jump to another URL based on certain condition, you could listen to the onClick event, process it, and then invoke Executions.sendRedirect(String) if it shall jump to another URL.

For end users, there is no difference between the use of Button.setHref(String) and Executions.sendRedirect(String).

		<button label="redirect" onClick="Executions.sendRedirect(&quot;another.zul&quot;)"/>
		<button label="href" href="another.zul"/>

Since the onClick event is sent to the server for processing, you are able to perform additional tasks before invoking Executions.sendRedirect(String), such as redirecting to another page only if certain conditions are satisfied.

On the other hand, the href property is processed at the client side. Your application won't be notified when users click the button.


[Since 5.0.4]

Button.setType(String) sets the button's type. It is designed to work with the HTML FORM tag. You rarely need it unless you want to work with HTML FORM and Servlets. For example,

<n:form action="/foo/my_handler" xmlns:n="native">
  <button type="submit" label="Submit"/>
  <button type="reset" label="Reset"/>


By specifying the upload property (Button.setUpload(String)), you could make a button used for uploading files. For example,

<button label="Upload" upload="true" onUpload="handle("/>

Once the file(s) are uploaded, the onUpload event will be sent with an instance of UploadEvent. And, you could retrieve the uploaded files from UploadEvent.getMedia() and UploadEvent.getMedias()

If you want to customize the handling of the file upload at the client, you can specify a JavaScript class when calling this method:

<button upload="foo.Upload"/> <!-- assume you implement a JavaScript class: foo.Upload -->

Another options for the upload can be specified as follows:

<button label="Upload" 
upload="true,maxsize=-1,multiple=true,accept=audio/*|video/*|image/*|MIME_type, native"/>


  • maxsize: the maximal allowed upload size of the component, in kilobytes, or a negative value if no limit.
  • native: treating the uploaded file(s) as binary, i.e., not to convert it to image, audio or text files.
  • multiple: treating the file chooser allows multiple files to upload, the setting only works with HTML5 supported browsers (since ZK 6.0.0)
  • accept: specifies the MIME types of files that the server accepts, the setting only works with HTML5 supported browsers (since ZK 7.0.0). MIME type list.

Customize Upload Size Exceeding Message

 since 8.0.0

If you want to customize the message about the file size exceeding max size, please refer to ZK Developer's Reference/Internationalization.

For Example, (in WEB-INF/

MZul.2105=The request was rejected because its size ({0}) exceeds the configured maximum ({1})

Notice that you can change the index {0} & {1} to choose the file size unit. (Auto:{0},{1} Byte:{2},{3} KB:{4},{5} MB:{6},{7})

Inherited Functions

Please refer to LabelImageElement for inherited functions.

Supported Events

Event Type
Event: Event

Denotes when a component gets the focus.

Event: Event

Denotes when a component loses the focus.

Event: UploadEvent

Denotes user has uploaded a file to the component.

Supported Molds

Available molds of a component are defined in lang.xml embedded in zul.jar.

Button mold default.png
Button mold trendy.png
Button mold os.png

Supported Children


Use Cases

Version Description Example Location
3.6 Get dynamically generated Button reference in onClick Event
3.6 How to fire onClick Event on a Button

Version History

Last Update : 2015/12/11

Version Date Content
5.0.4 August 2010 Button.setType(String) was introduced to allow a button able to submit or reset a form.
<n:form action="a_uri" xmlns:n="native">
  <button type="submit" label="Submit"/>
  <button type="reset" label="Reset"/>
6.0.0 December 2011 Button.setUpload(String) the multiple setting was introduced to allow to choose multiple files to upload at the same time. (HTML5 supported browsers only)
  <button upload="true,multiple=true" label="Fileupload"/>
7.0.0 September 2013 Button.setUpload(String) the accept setting was introduced to allow to specify the types of files that the server accepts. (HTML5 supported browsers only)
  <button upload="true,accept=audio/*|video/*|image/*|MIME_type" label="Fileupload"/>

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