Wicket Ajax

What ?

Since version 6.0 Wicket uses JQuery as a backing library for its Ajax functionality.

Why ?

The previous implementations of wicket-ajax.js and wicket-event.js were home baked solutions that worked well but also suffered from the differences in the browsers. Often users complained that some functionality doesn't work on particular version of particular browser. That's why the Wicket team chose to use JQuery to deal with browser inconsistencies and leave us to do our business logic.

Design and implementation

The new implementations (wicket-ajax-jquery.js and wicket-event-jquery.js) use JQuery internally but expose Wicket.** API similar to the previous version.

All Java components and behaviors should still use the Wicket.** API. This way if someday we decide to not use JQuery anymore we will have less work to do. Also if a user uses Dojo/YUI/ExtJS/... and prefer to not have JQuery in her application then she will be able to provide wicket-ajax-xyz.js implementation and replace the default one.

Table with renamed methods from the previous version

Configuration

Setup

To replace any of the JavaScript files the user application may use:

MyApplication#init():

public void init() {
  super.init();

  IJavaScriptLibrarySettings jsSettings = getJavaScriptLibrarySettings();

  jsSettings.setJQueryReference(new DojoReference());

  jsSettings.setWicketEventReference(new DojoWicketEventReference());
  
  jsSettings.setWicketAjaxReference(new DojoWicketAjaxReference());

}

Resource dependencies

Since Wicket 6.0 ResourceReference can have dependencies and it is recommended to properly define the dependency chain between this classes.
See the code of org.apache.wicket.ajax.WicketAjaxJQueryResourceReference to see how the default JQuery based implementation does that.

If the user application needs to upgrade/downgrade to new/old version of JQuery then just the first line above is needed:

  getJavaScriptLibrarySettings().setJQueryReference(new AnotherVersionOfJQueryReference());

AjaxRequestAttributes

Each Ajax behavior and component can use o.a.w.ajax.attributes.AjaxRequestAttributes to configure how exactly the Ajax call should be executed and how its response should be handled. To do this use:

AnyAjaxComponent/AnyAjaxBehavior.java:

  protected void updateAjaxAttributes(AjaxRequestAttributes attributes)
  {
      super.updateAjaxAttributes(AjaxRequestAttributes attributes);

      attributes.[set some attribute]();
  }

The available attributes are:

Attributes 'c' (component id) and 'u' (callback url) are automatically set by the Ajax behavior and they are not part of AjaxRequestAttributes.

While constructing the JavaScript that will register the event listener for that Ajax component/behavior these settings are serialized to optimized JSON object which is passed as a parameter to Wicket.Ajax.(get|post|ajax) methods.
For example an AjaxLink contributes JavaScript similar to :

  Wicket.Ajax.get({"u":"the/url/to/the/link", "e": "click", "c":"linkId"});

Many of the attributes have default values which are not written in the JSON settings and they are initialized at the client side (i.e. wicket-ajax.js knows the defaults). The example above can be read as: when HTML element with id 'linkId' is clicked fire an Ajax call with Url 'the/url/to/the/link'.

Migration steps

o.a.w.ajax.IAjaxCallDecorator is replaced with o.a.w.ajax.attributes.IAjaxCallListener.

Since Wicket Ajax now register DOM events (like click, change, ...) instead of using inline attributes like onclick, onchange, ... there is no more a script to decorate. Instead the new implementation provides points to listen to:

• before handler - executed before the data for the Ajax call is calculated. Even before the preconditions.
• precondition - if it returns false then the Ajax call (and all handlers below) is not executed at all
• beforeSend handler - executed before the actual execution of the Ajax call.
• after handler - if the Ajax call is asynchronous then it is executed right after its firing. If it is synchronous then it is executed after the complete handler
• success handler - executed on successful return of the Ajax call
• failure handler - executed on unsuccessful return of the Ajax call
• complete handler - executed on both successful and unsuccessful return

To use it do:
AnyAjaxComponent/AnyAjaxBehavior.java:

  protected void updateAjaxAttributes(AjaxRequestAttributes attributes)
  {
      super.updateAjaxAttributes(AjaxRequestAttributes attributes);

      AjaxCallListener myAjaxCallListener = new AjaxCallListener() {

        @Override public CharSequence getBeforeHandler(Component component) { return "alert('I\'m executed before the firing of the Ajax call')"; }
      };
      attributes.getAjaxCallListeners().add(myAjaxCallListener);
  }

There are also handy methods like onBefore(CharSequence), onComplete(CharSequence), ... but they do not provide access to the component which is bound with the Ajax behavior.

An Ajax request can have 0 or more IAjaxCallListener's.
o.a.w.ajax.attributes.AjaxCallListener is an adapter of IAjaxCallListener that implements all methods with noop bodies. If the body returns null or empty string then it is discarded.

Global Ajax call listeners

IAjaxCallListener's can be used to listen for the lifecycle of an Ajax call for a specific component.
If the user application needs to listen for all Ajax calls then it may subscribe to the following topics:

• /ajax/call/before
• /ajax/call/beforeSend
• /ajax/call/after
• /ajax/call/success
• /ajax/call/failure
• /ajax/call/complete

Those replaces the old Wicket.Ajax.(registerPreCallHandler|registerPostCallHandler|registerFailureHandler) methods and uses publish/subscribe mechanism.

Example (JavaScript):

    Wicket.Event.subscribe('/ajax/call/failure', function(jqEvent, attributes, jqXHR, errorThrown, textStatus) {
      // do something when an Ajax call fails
    });

All global listeners receive the same arguments as the respective IAjaxCallListener handler plus jQuery.Event that is passed by the PubSub system. This event is not the event that caused the Ajax call. The one that caused the Ajax call is 'attrs.event'.

Automatically migrated attributes.

Some of the attributes are available from the previous versions of Wicket as an overridable methods in AbstractDefaultAjaxBehavior. These methods are marked as deprecated and will be removed in Wicket 7.0 and for now Wicket automatically translates them into AjaxRequestAttributes.
These methods are:

• org.apache.wicket.ajax.AbstractDefaultAjaxBehavior#getPreconditionScript()
• org.apache.wicket.ajax.AbstractDefaultAjaxBehavior#getSuccessScript()
• org.apache.wicket.ajax.AbstractDefaultAjaxBehavior#getFailureScript()
• org.apache.wicket.ajax.AbstractDefaultAjaxBehavior#getChannel()

It is recommended to override org.apache.wicket.ajax.AbstractDefaultAjaxBehavior#updateAjaxAttributes(AjaxRequestAttributes) and configure those directly in the passed 'attributes'.

Tests for the client side Wicket Ajax functionality

At ajax.js you may see the currently available JavaScript unit tests that we have for the Ajax functionality in wicket-ajax.js

Blog articles

An introduction to the new functionalities are described at Wicket In Action. There is also a link to a demo application.

FAQ

How to check whether my custom version of the backing JavaScript library (jQuery) doesn't break Wicket internals somehow ?

1. Clone Wicket from its Git repository
   git clone http://git-wip-us.apache.org/repos/asf/wicket.git

1. Open wicket-core/src/test/js/all.html and change it to point to your version of the backing library.

1. Run the non-Ajax tests by opening file:///path/to/wicket/wicket-core/src/test/js/all.html

1. To run the Ajax tests see the description at the top of wicket-core/src/test/js/ajax.js. It is required to run them through Web Server

What parameters are passed to the handlers ?

1. before handler - attributes (the Ajax call attributes)
2. beforeSend handler - attributes, jqXHR (the jQuery XMLHttpRequest object), settings (the jQuery ajax settings)
3. after handler - attributes
4. success handler - attributes, jqXHR, data (the response), textStatus (the response status)
5. failure handler - attributes, errorMessage (the error message from jQuery)
6. complete handler - attrs, jqXHR, textStatus

The global listeners receive the same parameters prepended by jqEvent. This is the event triggered by jQuery. See section Global Ajax call listeners above.