How to cancel Ajax call

There are 2 buttons on a JSP page: One is called Search, another is called Cancel.

When the Search button is pressed, it will trigger an AJAX call, this ajax will call a Java function, while this java function makes a function call to the Oracle database (store procedure/function).

This searching process will take a while... At the mean time, the user wants to cancel the searching. So the user pressed the Cancel button.

Here, I want this cancel process to cancel the Ajax process;

How can I do that?

Thanks

Scott

The abort method may be what you need. http://www.google.com/search?q=ajax+abort

Does your server side script continue processing if the client is disconnected?

In conjunction with using abort, you can send another http request when canceling the request. This will set a session variable flag indicating the request is canceled. This flag should be checked in the server-side before performing extensive function calls. If canceled, the function call will not be performed.

Hi ,

Aborting a Ajax request ' sent ' already underway may not be that trivial .
Even you if you set a Session flag indicating that the action was cancelled later on. This Session information may not be available to the delegate call that is handling the Ajax request . As this thread doesnt even know what a Session is !!. Bcoz , HttpContext.Current would be null in that thread ( if using delegate ).

You need to figure out a way your executing server code can access a variable ( flag ) and abandon process based on that flag.

Just wanted to give you a heads up.

hmmm.

anybody find a solution to this?

Sometimes my proxy takes a long while, if it does - I want to abort the ajax and give a message ie.." Your request could not be completed at this time. Proxy server seems to be down."

etc.. Now, the proxy "might not be down", but just running VERY SLOW -- doens't matter. Either way, I want to kill the ajax call after a set time.

I was able to add canceling an action by using DWR. DWR is usually used to send messages from a server to a client, but you can also use it to send a message from a client to a server.

My client side jsp for the DWR setup is as follows:

<%@ taglib prefix="s" uri="/struts-tags" %>

<%-- These files are created in the runtime --%>
<script type='text/javascript' src='/rms/dwr/util.js'></script>
<script type='text/javascript' src='/rms/dwr/interface/PushMsg.js'></script>
<script type='text/javascript' src='/rms/dwr/engine.js'></script>

<div style="color:red" id="<%= session.getId()%>"></div>
<script type="text/javascript">
dwr.engine.setActiveReverseAjax(true);
PushMsg.initMsg();


function cancelAction() {
PushMsg.cancel();
}

</script>

On the server side the PushMsg class contains the cancel method and another method the check if cancel was pressed as follows:

public void cancel(){
servletContext.setAttribute("cancel", true);
}

public Boolean isCanceled(){
return (Boolean) servletContext.getAttribute("cancel");
}

The onclick event on my cancel button calls the cancelAction() function which in turn calls the cancel method of the PushMsg class on the server.
I just poll the PushMsg class on the server by calling the iscanceled() method.

You can find information and examples on using DWR at:
http://directwebremoting.org/dwr/index.html