I’ve had opportunity to use JBoss Seam from its 1.0 days, and also Spring Web Flow. I must admit that both frameworks really do hold their own in providing you with a full stack for rapid application development. This post does not attempt to look at these frameworks as a whole, but to focus on how easy it is to develop JSF
applications in them.
JSF is a Java standard for web application development. Therefore to judge any framework that depends on or claims to accelerate JSF, we will focus on how it scales over the gaping holes that are not handled by the standard, not just how they stick to it. Below are my observations. Note that the following points are not given in
any order of importance.
JSF’s UISelectItems Support
From somewhere in it’s 1.x version, Seam has provided the ability to use just a normal java.util.List of your own domain objects e.g. List<Student> directly to populate JSF’s UISelectItem controls like list boxes, drop down lists etc using their <s:selectItems/> component and it’s attached <s:convertEntity/> tag. Additionally, enums are easily handled in like manner using <s:convertEnum/> and <s:enumItem/>. This gets rid of the need to wrap domain objects in JSF SelectItem instances.
This is sorely lacking in Spring Faces, Spring’s JSF support for Web Flow, something I have even voted for in their JIRA instance.
Conversation Propagation in a Different Browser Tab
Seam provides the ability to invoke actions that start a new conversation or to move within states in a conversation using their provided <s:button/> or <s:link/> button and link respectively. Though Spring Faces has a Dojo backed
<sf:commandButton/> and <sf:commandLink/>, these are not yet capable of achieving this.
Integration with Hibernate Validator
Following the DRY principle, it can be very useful if JSF can also hook into the validation defined on your domain model using the defacto validation standard, Hibernate Validator. As you may already know, JSR-303 Bean Validation is targeted at standardizing the definition and enforcement of validation rules on your domain model,
with Hibernate Validator as the reference implementation. Seam provides the ability to enforce these validations in your JSF UI using the <s:validateAll/> tag.
Although requests have been made for this support, I’m yet to see it in Spring Faces.
Popup Screens
Sometimes it is cool to show modal panels for quick response from the user when interacting with the UI instead of a full page refresh. Spring Faces natively provides a Dojo based modal panel accessed just
by setting “popup” to true on any view state.
It is important to note however that though not natively supported in Seam, both it’s default JSF component library, RichFaces and the supported alternatives, ICEFaces and Trinidad, all provide this functionality
easily.
Display of byte[] images
JSF doesn’t provide any native control for the display of images from a byte array (byte[]) most probably retrieved from a database. The standard <h:graphicImage/> only deals with files accessible through a url. Seam however, provides support for display of images in a byte arrays using it’s <s:graphicImage/>.
There is no such support in Spring Faces, though RichFaces’s <a4j:mediaOutput/> could be used in displaying such content, however I have had problems using it with Spring Faces. ICEFaces also could be used to achieve this.
File Upload
Another vital component missing from the standard JSF toolkit is a file upload component of which Seam natively provides an <s:fileUpload/> component for achieving just that.
Unless you us a third party library like RichFaces or ICEFaces, I haven’t yet seen clear support for such a functionality in SpringFaces.
Rendering Components Based on Access Rights
Sometimes you want to hide a certain area of your UI from the user based on their roles/rights within the application. This is normally achieved in JSF using the “rendered” attribute on any tag or component. Seam provides a native way to easily hide or show components or sections using the s:hasRole EL function. An example of
this is below
<h:outputText value=”Hello”
rendered=”#{s:hasRole(‘Admin’)}”/>
This same support is extended to its “s:hasPermission” function, allowing you to render components on the UI based on not only roles, but fine grained permissions even backed by the Drools engine. And these functions are accessible whether on the UI, in your navigation rules (when you use pages.xml or pdl) and even in your code on annotations.
Spring Faces has no native support for this on facelets (I think it’s only available on jsps). However, an open-source project, Acegi-JSF, has a UI component tag <acegijsf:authorize/> and other additional ones which allow you to render based on access rights. This is limited, in that it cannot be applied to the rendered” attributes of JSF components since it is by itself a component/tag, not an EL function like Seam’s approach. You have to be quite inventive (and verbose) to come up with your own solutions to this problem.
Extended EL Capabilities
JSF 1.2 is limited in it’s EL support, and as a result you cannot invoke an action with parameters on a facelet. The following is not allowed, though I’ve seen proposals to fix it natively in
<h:commandButton action=”#{shop.buyProduct(product)}”/>
Seam uses it’s own implementation of the EL-API called the JBoss EL, and this allows the invocation of such actions in a facelet and in your navigation rules.
Though Spring Faces also uses JBoss EL, for some reason I haven’t been able to do anything like the above in my facelet, though it is possible in flow (it is a heavily used feature Spring Web Flow).
Automatic Detection of Converters & Validators Through Annotations
One may be forced to write some converters or validators needed to meet specific business logic needs. JSF requires you to specify these classes in it’s faces-config.xml file before being used.
Seam provides annotations for auto-discovering JSF converters and validators, meaning there is no need for the “xml hell” when creating these components.
Spring Faces doesn’t yet have this support.
TimeZones & Themes
The JSF specification assumes that all dates and times are UTC. To override this behaviour, a timezone must specified using an <f:convertDateTime/> on each date being displayed. The inconvenience of this cannot be overstated as I’ve had to deal with this. Using a Seam component on which the Time Zone may be specified in your application, Seam overrides this behaviour in your JSF application, a feature I’m yet to see in SpringFaces.
Also, most of today’s webapps come with the ability to change themes on the fly, but JSF has no native support for themes. This support however is provided by Seam in a very easy to configure way, and is yet to make it to Spring Faces.
Tools
JSF by nature is designed with tools in mind, as result, tool support is an important part of adoption of JSF and every JSF framework’s tool support must be brought under the scope.
JBoss provides JBoss Tools, a superb set of tools for rapid application design. It’s Richfaces VPE provides wysiwyg, drag n’ drop design of facelets with a palette of HTML,JSF, Facelets and Richfaces components. It also supports resolution of your seam components inside facelet using Seam component names as well as wysiwyg declaration of
nagivation rules in both the standard JSF faces-config.xml or and Seam’s pages.xml. Even resolution of component names in code is also available. See the JBoss Tools Developer Guide for more on this toolset.
Spring provides it’s own Spring IDE set of tools which also allow the resolution of Spring beans within your flow definitions. Unfortunately, there isn’t any wysiwig support and Spring beans cannot be resolved by the Richfaces VPE.
Other Non-JSF Stuff For UI Developers
Conversation Switcher
With both frameworks promising the ability to have long running conversations, it then becomes useful to be able to start different conversations concerning different things, and have knowledge on the UI of which conversations have been started and the state in which the user is in each conversation.
This is natively supported in Seam but not in Web Flow.
Debug page
It helps to know the state and content of the beans in your scopes, especially when you want to know why certain things are not showing up on your facelet, without having to set break points in your IDE and start a whole debugging process.
Seam gives you the ability to at any time in any conversation, see the contents of your components in their appropriate scopes. This I sorely missed in Web Flow.
Summary
There are a host of other things that we could also compare, but from these ones it is not difficult to see why people who develop using the JSF framework see Seam as a saviour. We could choose
to chastise JSF itself for its shortcomings and use other frameworks but when someone comes along and makes standards like JSF more attractive as their first priority, I think they deserve the support and commendation. And that is what I believe is the problem with Spring Web Flow and it’s
Spring Faces project.
Spring has it’s own MVC framework, SpringMVC which predates Web Flow. Web Flow can be developed either using SpringMVC or JSF aka Spring Faces. A lot of the limitations of Spring Faces noted here are already handled natively by SpringMVC. Obviously, Spring Faces has not had the kind of attention that the first class citizen, SpringMVC
has in the world of Spring. In fact, one wonders if the sudden entrance of Spring Faces is not just a knee jerk reaction to Seam winning the JSF folks over.
I believe that if you had to develop a JSF application and did not have any investments in Spring already, it will make more sense to go for Seam as your preferred framework. Coupled with it’s advanced tooling, there isn’t as yet a better choice. Trust me, you won’t regret it.
Seam also has support for other web frameworks like GWT and Wicket. Though Seam’s support of Wicket is very young, it will be interesting to see what
the community’s acceptance of it is.
Technorati Tags: seam, web flow, jsf, jboss, spring
Edem Morny's Tech Blog 