Posts Tagged MyFaces
How to configure JSF to get the browser Back button working
Lately, I had a problem with one of my JSF applications which is using RichFaces.
The problem was happening when the user was hitting the browser Back button. Well, you would say that it is a usual problem in web development. But still, because we cannot disable the browser Back button, the web application needs to work fine if the user decides to click on it!
Anyway, let’s get back on topic. As I said, the problem occurred if the user was clicking on the Back button but the funniest thing is it was happening when he was clicking twice on it! Why did it work fine when clicking once but not twice? 
The solution is quite simple actually.
It was coming from one of the options in MyFaces configuration: com.sun.faces.numberOfViewsInSession.
Here is a quick explanation of this option:
com.sun.faces.numberOfViewsInSession
Specifies the number of views that are stored in the session when Server-Side State Saving is used. If set to true while client-side state saving is being used, reduces the number of bytes sent to the client by compressing the state before it is encoded and written as a hidden field. The default for this parameter is 15.
So basically, JSF is storing each page previously viewed by the user in session. And, as you can see from the description above, JSF will stored a maximum of 15 pages by default. However, it was set to 1 in my application, which means only ONE page would be stored…
This was obviously the reason why the application was working fine if the user was clicking only once on the Back button but not twice! 
For the same reason, you should also check the option org.apache.myfaces.NUMBER_OF_VIEWS_IN_SESSION which is default to 20:
org.apache.myfaces.NUMBER_OF_VIEWS_IN_SESSION
Defines the number of the latest views that are stored in session. This option is only applicable if the state saving method is set to server. The default for this parameter is 20.
For more information about JSF options, please have a look at the following page:
http://publib.boulder.ibm.com/infocenter/wasinfo/v7r0/index.jsp?topic=/com.ibm.websphere.express.doc/info/exp/ae/rweb_jsfengine.html
The message tags of MyFaces and RichFaces
Working on an application using MyFaces and RichFaces, I had no choice but understand what is the difference between the message tag provided by Myfaces (h:message) and the message tag overridden by RichFaces (rich:message).
These tags allow to display information about the first FacesMessage that is assigned to the component referenced by the “for” attribute. The difference is that the RichFaces tag has some extra functionalities such as Ajax rendering, error markers and predefined css class names.
Have a look at the following page for more details: http://livedemo.exadel.com/richfaces-demo/richfaces/message.jsf
This is all nice and well but it is not the only difference. Indeed, the HTML code generated by both these frameworks will also be different!
First of all, let’s see how the tag <h:message styleClass="errormsg" for="element"/> will be transformed. If there is no message to display, nothing will be generated (which is a good behaviour). However, if a message is present, the tag will be replaced by the following HTML code:
<span class="errormsg">Required.</span>
So far, so good!
But now let’s check what code RichFaces is generating for the tag <rich:message styleClass="errormsg" for="element"/>.
The following is the code created if there is NO message to render:
<span class="rich-message errormsg" id="form:j_id255">
<span class="rich-message-label"></span>
</span>
And here is the code which will replace the RichFaces tag if there is a message to display:
<span id="bookingform:j_id255" class="rich-message errormsg">
<span class="rich-message-label">Required.</span>
</span>
As you can see, the main difference is that RichFaces is wrapping the original span tag into another span tag. But, it is also generating some code even if there is no message to display! You would ask why is it doing that? The response is simple. The wrapper span element is necessary for RichFaces to Ajax-render the message tag if an error message has to be displayed for the targeting element.
So make sure you don’t put any padding or margin style in your custom CSS class which I called ‘errormsg’ in my example. Otherwise, you might have a gap when you were expecting nothing… (this happened to me) 