What are the main disadvantages of Java Server Faces 2.0?

After 5 years of working with JSF, I think that I can add my 2 cents.

Two major JSF drawbacks:

1. Big learning curve. JSF is complex, that's just true.
2. Its component nature. Component-based framework tries to hide the true nature of the Web, which comes with a huge amount of complications and disasters (like not supporting GET in JSF within almost 5 years).
   IMHO hiding HTTP Request/Response from the developer is an enormous mistake. From my experience, every component-based framework adds abstraction to the Web development, and that abstraction results in unnecessary overhead and higher complexity.

And minor drawbacks that come to my mind:

1. By default ID of the object is composed of its parents' ids, for example form1:button1.
2. No easy way to comment-out incorrect page's fragment. Tag <ui:remove> needs syntactically correct content which is parsed anyway.
3. Low quality 3rd party components which e.g. don't check isRendered() inside processXxx() method before continuing.
4. Incorporating LESS & Sencha is hard.
5. Doesn't play well with REST.
6. Not so easy for UX designers, because ready-to-use components have their own CSS styles, that need to be overwritten.

Don't get me wrong. As a component framework JSF in version 2 is really good, but it's still component-based, and always will be...

Please take a look at the low popularity of Tapestry, Wicket and low enthusiasm of experienced JSF developers (what is even more meaningful). And for contrast, take a look at the success of Rails, Grails, Django, Play! Framework - they all are action-based and don't try to hide from the programmer true request/response and stateless nature of the web.

For me it's major JSF disadvantage. IMHO JSF can suits some type of applications (intranet, forms-intensive), but for real-life web application it's not a good way to go.

Hope it helps somebody with his/her choices that regards to front-end.

JSF 2.0 disadvantages? Honestly, apart from the relative steep learning curve when you don't have a solid background knowledge about basic Web Development (HTML/CSS/JS, server side versus client side, etc) and the basic Java Servlet API (request/response/session, forwarding/redirecting, etc), no serious disadvantages comes to mind. JSF in its current release still needs to get rid of the negative image it gained during the early ages, during which there were several serious disadvantages.

JSF 1.0 (March 2004)

This was the initial release. It was cluttered with bugs in both the core and performance areas you don't want to know about. Your webapplication didn't always work as you'd intuitively expect. You as developer would run hard away crying.

JSF 1.1 (May 2004)

This was the bugfix release. The performance was still not much improved. There was also one major disadvantage: you can't inline HTML in the JSF page flawlessly. All plain vanilla HTML get rendered before the JSF component tree. You need to wrap all plain vanilla in <f:verbatim> tags so that they get included in the JSF component tree. Although this was as per the specification, this has received a lot of criticism. See also a.o. JSF/Facelets: why is it not a good idea to mix JSF/Facelets with HTML tags?

JSF 1.2 (May 2006)

This was the first release of the new JSF development team lead by Ryan Lubke. The new team did a lot of great work. There were also changes in the spec. The major change was the improvement of the view handling. This not only fully detached JSF from JSP, so one could use a different view technology than JSP, but it also allowed developers to inline plain vanilla HTML in the JSF page without hassling with <f:verbatim> tags. Another major focus of the new team was improving the performance. During the lifetime of the Sun JSF Reference Implementation 1.2 (which was codenamed Mojarra since build 1.2_08, around 2008), practically every build got shipped with (major) performance improvements next to the usual (minor) bugfixes.

The only serious disadvantage of JSF 1.x (including 1.2) is the lack of a scope in between the request and session scope, the so-called conversation scope. This forced developers to hassle with hidden input elements, unnecessary DB queries and/or abusing the session scope whenever one want to retain the initial model data in the subsequent request in order to successfully process validations, conversions, model changes and action invocations in the more complex webapplications. The pain could be softened by adopting a 3rd party library which retains the necessary data in the subsequent request like MyFaces Tomahawk <t:saveState> component, JBoss Seam conversation scope and MyFaces Orchestra conversation framework.

Another disadvantage for HTML/CSS purists is that JSF uses the colon : as ID separator character to ensure uniqueness of the HTML element id in the generated HTML output, especially when a component is reused more than once in the view (templating, iterating components, etc). Because this is an illegal character in CSS identifiers, you would need to use the \ to escape the colon in CSS selectors, resulting in ugly and odd-looking selectors like #formId\:fieldId {} or even #formId\3A fieldId {}. See also How to use JSF generated HTML element ID with colon ":" in CSS selectors? However, if you're not a purist, read also By default, JSF generates unusable ids, which are incompatible with css part of web standards.

Also, JSF 1.x didn't ship with Ajax facilities out of the box. Not really a technical disadvantage, but due to the Web 2.0 hype during that period, it became a functional disadvantage. Exadel was early to introduce Ajax4jsf, which was thoroughly developed during the years and became the core part of JBoss RichFaces component library. Another component libraries were shipped with builtin Ajax powers as well, the well known one being ICEfaces.

About halfway the JSF 1.2 lifetime, a new XML based view technology was introduced: Facelets. This offered enormous advantages above JSP, especially in the area of templating.

JSF 2.0 (June 2009)

This was the second major release, with Ajax as buzzword. There were a lot of technical and functional changes. JSP is replaced by Facelets as the default view technology and Facelets was expanded with capabilities to create custom components using pure XML (the so-called composite components). See also Why Facelets is preferred over JSP as the view definition language from JSF2.0 onwards?

Ajax powers were introduced in flavor of the <f:ajax> component which has much similarities with Ajax4jsf. Annotations and convention-over-configuration enhancements were introduced to kill the verbose faces-config.xml file as much as possible. Also, the default naming container ID separator character : became configurable, so HTML/CSS purists could breathe relieved. All you need to do is to define it as init-param in web.xml with the name javax.faces.SEPARATOR_CHAR and ensuring that you aren't using the character yourself anywhere in client ID's, such as -.

Last but not least, a new scope was introduced, the view scope. It eliminated another major JSF 1.x disadvantage as described before. You just declare the bean @ViewScoped to enable the conversation scope without hassling all ways to retain the data in subsequent (conversational) requests. A @ViewScoped bean will live as long as you're subsequently submitting and navigating to the same view (independently of the opened browser tab/window!), either synchronously or asynchronously (Ajax). See also Difference between View and Request scope in managed beans and How to choose the right bean scope?

Although practically all disadvantages of JSF 1.x were eliminated, there are JSF 2.0 specific bugs which might become a showstopper. The @ViewScoped fails in tag handlers due to a chicken-egg issue in partial state saving. This is fixed in JSF 2.2 and backported in Mojarra 2.1.18. Also passing custom attributes like the HTML5 data-xxx is not supported. This is fixed in JSF 2.2 by new passthrough elements/attributes feature. Further the JSF implementation Mojarra has its own set of issues. Relatively a lot of them are related to the sometimes unintuitive behaviour of <ui:repeat>, the new partial state saving implementation and the poorly implemented flash scope. Most of them are fixed in a Mojarra 2.2.x version.

Around the JSF 2.0 time, PrimeFaces was introduced, based on jQuery and jQuery UI. It became the most popular JSF component library.

JSF 2.2 (May 2013)

With the introduction of JSF 2.2, HTML5 was used as buzzword even though this was technically just supported in all older JSF versions. See also JavaServer Faces 2.2 and HTML5 support, why is XHTML still being used. Most important new JSF 2.2 feature is the support for custom component attributes, hereby opening a world of possibilities, such as custom tableless radio button groups.

Apart from implementation specific bugs and some "annoying little things" such as inability to inject an EJB in a validator/converter (already fixed in JSF 2.3), there are not really major disadvantages in the JSF 2.2 specification.

Component based MVC vs Request based MVC

Some may opt that the major disadvantage of JSF is that it allows very little fine-grained control over the generated HTML/CSS/JS. That's not JSF's own, that's just because it's a component based MVC framework, not a request (action) based MVC framework. If a high degree of controlling the HTML/CSS/JS is your major requirement when considering a MVC framework, then you should already not be looking at a component based MVC framework, but at a request based MVC framework like Spring MVC. You only need to take into account that you'll have to write all that HTML/CSS/JS boilerplate yourself. See also Difference between Request MVC and Component MVC.

See also:

• What is the difference between JSF, Servlet and JSP? (just to understand the basics)
• Using JSF to develop tableless CSS layouts (another myth about JSF)
• JSF vs plain HTML/CSS/JS/jQuery (when JSF is the wrong choice)
• Design patterns in web applications (illustrates the ideology behind MVC)