Preventing multiple form submits in ICEFaces by disabling commandButton

I created a form in ICEFaces 2 to upload a file. ICEFaces 2 has a new component for files, called the fileEntry (see http://wiki.icefaces.org/display/ICE/FileEntry). The old inputFile component has been removed from ICEFaces 2. Uploading a file takes a while, and I quickly noticed the user could click the "upload" button multiple times while the upload was in progress. This is obviously something you want to prevent. There is a very easy approach to this: just disable the submit button once it has been pressed. All you need to do is add this code to the commandButton tag:

onclick="this.disabled=true"

This works fine, and if you always go to a new page after the form has been submitted this is all you have to do. In most applications this unfortunately won't be the case: if something goes wrong with the file upload or if some other form components fail validation, you will want to stay on the same page, giving the user a warning message and allowing him to try again. The problem is that your commandButton is now disabled, so the user can't try again...
Re-enabling the commandButton when the action finishes is not as easy as it may seem: there's no "onAfterSubmit" action or something similar on the form. My first try was to add the disabled property with a value of "false":

disabled="false"

I thought that ICEFaces would re-evaluate the form after the submit, causing it to reset the disabled property to false. Unfortunately ICEFaces is smarter than that, and uses a technique called "partial dom updates". What this means is it checks if any of the components properties were changed in the action and it will only update those components whose properties have actually changed. This is a smart technique, since it reduces http traffic. It also means that our commandButton will not be updated, since for ICEFaces nothing changed to this component (it isn't aware of the JavaScript function we performed on it). This means we will have to trick ICEFaces into thinking a property of our commandButton has actually changed, causing it to refresh the commandButton. I choose to "abuse" the styleClass property for this use. I set it to:

styleClass="#{backingBean.randomValue}"

Then in my backing bean I implemented the getter for this value as follows:

public String getRandomValue() {
return "a" + System.currentTimeMillis();
}

This ensures we will get a different value for the styleClass property on each form submit. This will trick ICEFaces into thinking the commandButton has changed, causing it to refresh it and setting the disabled value to false, effectively re-enabling our commandButton.

I agree this approach isn't very clean, but it's the only technique I found to accomplish this in ICEFaces. If anyone knows of a better way, I'd be glad to know!

ICEFaces 2.0 charts migration

Today I was upgrading an ICEFaces 1.8 / JSF1.2 project to ICEFaces 2 and JSF 2. Everything worked well, except my charts weren't displayed anymore. After snooping around in the ICEFaces code, I found out that they used a new JSF 2 mechanism to serve the chart images, called resource handlers. The problem is that the ICEFaces resource handler URL isn't handled by the JSF servlet. This means the resource handler never gets executed. To make sure it gets executed, you should add the mapping to your web.xml file as follows:

<servlet-mapping>
<servlet-name>Faces Servlet</servlet-name>
<url-pattern>/icefaces/*</url-pattern>
</servlet-mapping>

This will make the charts visible again. The same goes for the DataExporter component, which also doesn't work as long as you don't add this mapping.

Slow ICEFaces

ICEfaces (http://www.icefaces.org) is a great JSF framework. I recently developed an application using ICEfaces. On my development machine, everything worked well. However, when I deployed the application to our Linux test server, the whole application became very slow (I'm talking about 20 seconds per request).
After profiling the application, I found out that ICEfaces wraps each HttpServletRequest object to have a uniform interface over all the different Servlet specification versions. It caches some of the values from the HttpServletRequest, and there lies the culprit: one of the values it caches is the getLocalName() value. How this method is implemented depends on your Servlet container, but on apache it results in a call to InetAddress.getHostName(). InetAddress.getHostName() will perform a reverse DNS lookup on its IP address. And there lies the problem: our test server doesn't have a DNS entry, so this method fails (after trying for a very long time). Java will also not cache failed DNS lookup values (you can enable this, see http://download.oracle.com/docs/cd/E17476_01/javase/1.5.0/docs/guide/net/properties.html, but I wouldn't recommend doing so).

So there are 2 possible solutions:

1. Add a DNS entry for your server (either in your DNS server or in the etc/hosts file or similar)
2. Sometimes modifying the DNS is not possible (for any number of reasons). Another solution would be to create a Filter that overrides the default behavior of HttpServletRequest.getLocalName(). Here's an example:

public class LocalNameFilter implements Filter {

public void destroy() {
}

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
HttpServletRequest hsr = (HttpServletRequest) request;  
ServletRequestWrapper wrapper = new HttpServletRequestWrapper(hsr) {
@Override
public String getLocalName() {    
return "myHost";
}
};
chain.doFilter(wrapper, response);
}

public void init(FilterConfig fConfig) throws ServletException {
}

}

Don' forget to declare this filter in your web.xml:

<filter>  
<display-name>LocalNameFilter</display-name>
<filter-name>LocalNameFilter</filter-name>
<filter-class>com.xxx.web.LocalNameFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>LocalNameFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>