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Just what is Java EE really? [closed]

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Closed 9 years ago.
Java EE has this "mysterious shroud" around it for younger Java developers - one that I've been trying to lift myself for quite a while with little success.
Confusion arises from:
Java EE seems to be both a library and a platform - there are multiple ways to "get" the Java EE library, typically from something like Oracle's Java EE SDK download. However, the Java EE library will not work, nor compile unless if your code is being run on or has access to a Java EE application server (such as JBoss, GlassFish, Tomcat, etc). Why? Can't the libraries function outside of the application server environment? Why do I need something massive as JBoss just to compile simple code to send an email?
Why are Java EE libraries not "standard" and included in the regular JVM download and/or the SDK?
Why are there so many Java EE offerings when there is really only two main flavors of standard Java (Oracle JVM/SDK | OpenJDK JVM/JDK)?
What can one do with Java EE that they cannot do with standard Java?
What can one do with standard Java that they cannot do with Java EE?
When does a developer decide they "need" Java EE?
When does a developer decide they do not need Java EE?
Why is Java EE library version not in sync with standard Java library releases (Java EE 6 vs. Java 7)?
Thanks for helping me clear the flog!

Why can't the libraries function outside of the application server environment?
Actually they can. Most of the libraries can be directly used standalone (in Java SE) or included in a .war (practically that's nearly always Tomcat). Some parts of Java EE, like JPA, have explicit sections in their respective specifications that tells how they should work and be used in Java SE.
If anything, it's not so much an application server environment per se that's at stake here, but the presence of all other libraries and the integration code that unites them.
Because of that, annotations will be scanned only once for all your classes instead of every library (EJB, JPA, etc) doing this scanning over and over itself. Also because of that, CDI annotations can be applied to EJB beans and JPA entity managers can be injected into them.
Why do I need something massive as JBoss just to compile simple code to send an email?
There are a few things wrong with this question:
For compiling you only need the API jar, which is below 1MB for the Web Profile, and a little over 1MB for the full profile.
For running you obviously need an implementation, but "massive" is overstating things. The OpenJDK for example is around 75MB and TomEE (a Web Profile implementation containing mail support) is only 25MB. Even GlassFish (a Full Profile implementation) is only 53MB.
Mail works perfectly fine from Java SE (and thus Tomcat) as well using the standalone mail.jar and activation.jar.
Why are Java EE libraries not "standard" and included in the regular JVM download and/or the SDK?
Java EE in a way was one of the first attempts to split up the already massive JDK into chunks that are easier to manage and download. People are already complaining that the graphical classes (AWT, Swing) and Applets are inside the JRE when all they do is run some commands on a headless server. And then you also want to include all the Java EE libraries in the standard JDK?
With the eventual release of modularity support we'll just have a small base JRE with many things separately installable as packages. Perhaps one day many or even all classes that now make up Java EE will be such package as well. Time will tell.
Why are there so many Java EE offerings when there is really only two main flavors of standard Java (Oracle JVM/SDK | OpenJDK JVM/JDK)?
There are more than just two flavors of Java SE. There is at least the IBM JDK, the previous BEA one (JRocket, which is being merged into the Oracle/Sun one because of the acquisition), various other open source implementations and a slew of implementations for embedded use.
The reason behind Java SE and EE being a specification is that many vendors and organizations can implement it and thus it encourages competition and mitigates the risk of vendor lock-in.
It's really no different with C and C++ compilers, where you have many competing offerings as well all adhering to the C++ standard.
Why is Java EE library version not in sync with standard Java library releases (Java EE 6 vs. Java 7)
Java EE builds on Java SE, so it trails behind. The versions do correspond though. Java EE 5 requires Java SE 5. Java EE 6 requires Java SE 6 and so on. It's just that mostly when Java SE X is current, Java EE X-1 is current.

Here are a few quickly composed answers to your questions...
Why can't JavaEE libraries function without an application server?
The services provided by JavaEE (container managed transactions, container managed dependency injection, timer service, etc..) inherently involve JavaEE compliant Application Servers (for example: GlassFish, JBoss, WebSphere, etc...). Therefore the JavaEE libraries serve no purpose without such a container. "Why do I need something as massive as JBoss just to compile simple code to send an email?" You don't. There are ways to send an email without JavaEE... But if you want to do it the JavaEE way, you need a JavaEE container.
Why are JavaEE libraries not included with JavaSE download?
The same reason that many libraries aren't included: it would be overkill. Since you can't even use the JavaEE libraries without an application server, why bother to include them? JavaEE should be downloaded if and when a developer installs an application server and decides to use JavaEE.
Why are there so many JavaEE offerings?
Are there really "so many" JavaEE offerings? If so, please list some of them. More accurately I believe there are multiple implementations of the same APIs.
What can one do with JavaEE that they can't do without standard Java?
Lots. You can't rely on an application server to manage transactions or persistence contexts without JavaEE. You can't allow an application server to manage EJB dependency injection without JavaEE. You can't use an application managed timer service without JavaEE. The answer to this question should make the answer to the first question quite clear... Most of the services provided by JavaEE require a JavaEE container.
What can you do with JavaSE that you can't do with JavaEE?
Um... I don't know.
When does a developer decide they need JavaEE?
This question is completely subjective... But if you need any of the services provided by JavaEE, you start to think about it. If you don't know what JavaEE is... you probably don't need it.
When does a developer decide they do not need JavaEE?
See previous answer.
Why is JavaEE library version not in sync with JavaSE version?
Good question. I won't pretend to know how to answer it... But I would guess the answer is: "because they're not in sync".

At bird's eye view, Java EE is a platform, i.e. something that we can build on.
Taking a more technical perspective, the Java Enterprise Edition standard defines a set of APIs commonly used for building enterprise applications. These APIs are implemented by application servers - and yes, different application servers are at liberty to use different implementations of the Java EE APIs.
However, the java ee library will not work, nor compile unless if your code is being run on or has access to a Java EE application server (such as JBoss, GlassFish, Tomcat, etc).
You compile against the Java EE APIs, so you only need those APIs at compile time. At runtime, you'll also need an implementation of these APIs, i.e. an application server.
Why do I need something massive as JBoss just to compile simple code to send an email?
You don't. However, if you wish to use the Java EE API for sending mail, you will need an implementation of that API at runtime. This can be provided by an application server, or by provided by a stand alone library you add to your classpath.
Why are Java EE libraries not "standard" and included in the regular JVM download and/or the SDK?
Because only the APIs are standardized, not the implementations.
Why are there so many Java EE offerings
Because people disagree on the right way to implement certain features. Because different vendors compete for market share.
What can one do with Java EE that they cannot do with standard Java?
Since Java EE implementations are built with "standard Java": Nothing. However, leveraging the existing libraries can save a great deal of effort if you are solving typical enterprise problems, and using a standardized API can prevent vendor lock-in.
What can one do with standard Java that they cannot do with Java EE?
Nothing, since Java EE includes Java SE.
When does a developer decide they "need" Java EE? When does a developer decide they do not need Java EE?
Generally speaking, the Java EE APIs solve typical, recurring problems in enterprise computing. If you have such problems, it usually makes sense to use the standard solutions - but if you have different problems, different solutions may be called for. For instance, if you need to talk to a relational database, you should consider using JPA. But if you don't need a relational database, JPA won't help you.

What is Java EE?
Let's start from canonicity definition at wiki:
Java Platform, Enterprise Edition or Java EE is Oracle's enterprise
Java computing platform. The platform provides an API and runtime
environment for developing and running enterprise software, including
network and web services, and other large-scale, multi-tiered,
scalable, reliable, and secure network applications.
The main point here is that Java EE is a platform provides an API, not some concrete library.
What for Java EE needed?
The main scope of Java EE is the network based applications, unlike Java SE oriented to the desktop applications development with simple network support. This is the main diference between them.
Scalability, messaging, transactioning, DB support for every application... the need in all of this has increased with the evolution of the network.
Of course a lot of ready solutions which Java SE provides are useful for network development, so Java EE extends Java SE.
Why do we need application servers to run our code?
Why do we need operation systems? Because there are a lot of painful work with hardware we need to do to make even simpliest application. And without OS you need to do it again and again. Oversimplified OS is just a programmatic container, which provides us a global context to run our applications.
And this is what the application servers are. They are allows us to run our applications in their context and provides us a lot of highlevel functionality which is needed for enterprise highloaded network applications. And we are don't want to write our own bicycles to solve this problems, we are want to write code which will satisfy our business needs.
Another example here could be JVM for Java.
Why Java EE doesn't contains onboard app server?
Hard to say for me. I think, it was done for more flexibility. Java EE says what they should do, they decide how to do it.
Why JVM doesn't include Java EE?
Because they directed to different market sectors. Java EE has a bunch of functionality which is doesn't need for usual desktops.
Why are there so many Java EE offerings?
Because Java EE only describes the behaviour. Everybody can implement it.
What can one do with Java EE that they cannot do with Java SE?
To conquer the internet. It's really hard to do with Java SE applets and sockets :)
What can one do with Java SE that they cannot do with Java EE?
As mentioned above Java EE extends Java SE, so with Java EE you should be able to do everything what is available for Java SE.
When does a developer decide they "need" Java EE?
When they need the power of Java EE. All what is mentioned above.
When does a developer decide they do not need Java EE?
When they write a usual console or desktop application.
Why versions of Java SE and Java EE are unsynced?
Java always had troubles with it's technologies naming and versioning. So this situation is not an exception.

Java EE is all about container concept. Container is an execution context within which will run your application and which provide this last a set of services. Each kind of service is defined by a specification named JSR. For example JSR 907, JTA (java transaction Api) which provide a standard way to manage distributed transaction against different resources. There are generally many different implementations for a given JSR, the implementation you will use depends on the container provider, but you don't really mind about that as you are sure the behavior respect the predefined contract : the JSR API. So to take advantage of Java EE, you need to run your application inside a container. The two main ones are EJB and servlet container which are both present on any Java EE certified application server.
The aim of all of this is to defined a standard execution environment to allow to package your application with only the essentials, id.est. your business. It avoids to depend on a unknown and various set of third-party libraries that you would have to package and provide with your app otherwise, and which may be sources of conflict with other apps on the server. In Java EE you know that all standard non functional requirements like security, transaction, scalability, remote invocation, and many more will be provided by the container (factorized for all apps running inside it) and you just have to base your work on its.

how do java frameworks relate to java platform

I can code in Java, and I'm trying to understand the wiki article on frameworks and how they relate to java. I think java = the platform and the frameworks are things like Java EE, jsp, etc. (I've never used any of those)
I'm trying to see the connection here.... Also, does each framework get its own compiler? Do they all use the JVM?

From my understanding: Java is a programming language (that compiles through the JVM), it is "open source" and can be extended with different APIs. Java EE (Enterprise Edition) is an API of Java SE (Standard Edition), it adds more functionality to the Standard API of Java.
Frameworks are supposed to make programming in languages like Java easier, and decrease development time. For example a framework named "Play" is a pretty popular java framework that helps develop web pages. Frameworks are not seperate from the language, they use the language itself so they don't get their own compiler all it's doing is using the language.
Someone (or a company) just creates their own methods in java and make them available to use for anyone that wants to use it. Anyone can create a framework, you can probably think of a framework as a Lego set where each Lego piece is a method available to build your own program (or website, depending on what the framework was created for), eventually you can build your own program using those methods from the framework. (hope this is making sense, heh)

Strictly speaking Java is a programming language. Just a programming language. It needs an implementation if you are to compile and run programs.
The Java implementation(s) consist of bytecode compilers and related tools, and a runtime platform. The runtime platform consists of an implementation of the Java Virtual Machine (JVM), together with the runtime libraries that contain the standard classes.
There are in three primary Sun/Oracle Java "platform" types ... or Editions as they are called:
Java Standard Edition (SE) is the normal general purpose platform. Unless specified otherwise, this is what most people will be using.
Java Micro Edition (ME) is designed for embedded devices such as smart phones, set-top boxes and the like. It is a very cut-down version of Java, with some significant differences in some area.
Java Enterprise Edition (EE) is an extended platform designed to support enterprise computing. It adds support for web server development, component-based systems (EJB) and other things. (In fact J2EE is a bit more woolly than this, because there are web container distributions out there like Tomcat, Jetty and so on that provide a subset of the Java EE technologies ... on top of a standard Java SE platform.)
A framework is a different idea. Frameworks are typically systems of libraries that support a particular way of designing and implementing software applications. So for instance:
The core Spring Framework supports a style of programming where the system is "wired up" from a bunch of components at start up.
Spring MVC (and other frameworks) support web servers that are implement according to the Model-View-Controller design pattern.
A RESTful web server framework supports web servers that follow the RESTful model.
And so on.
These frameworks typically run on one or more kind of Java platform, depending on what they are doing.
Also, you could make a case that some of the technologies that are in Java EE platform are actually framework technologies. Servlets and EJBs are prime examples.

If you are familiar with jQuery in javascript, well jQuery is a javascript framework. Same goes for framework for java. It just makes programming easier

Way to keep minimal application-server dependency?

What is the best (easiest, most seamless) way to build a Java app while relying as little as possible on the actual application-server used in deployment?
For example, say I want to deploy on Apache Geronimo, and later want to use GlassFish, how difficult would the transition be? What is the best way to abstract the use of each app server?
Excuse my ignorance, I'm relatively new to Java development. I want to start a new project, but am unsure on whether to use separate APIs for the functionality I need or develop on top of a chosen app-server from the start.
Thanks for your help,
Ivan

Without getting into too much details, even though you can write bare-bones Java EE code, the configuration around it is not very simple. Each application server has its own set of configuration files and naming conventions (for example, the format for specifying the location of the AS is different in IBM WAS and in JBOSS). Though these are not very important for application development, once you get to the deployment phase, these will become important.
As far as the libraries and your code is concerned as long as you stick to EJB standards you will be able to run your application on majority of the application servers (I know of WAS and JBoss - the code that I wrote didn't have to change for these servers; the configuration though, well that was a different beast !).

Follow Java EE specification as much as possible, while follow server specification least as possible.
If we try to find out what are in common among there Java EE application servers(JBoss, WAS...), answer is Java EE specification which server vendors must follow. If you have 2 solutions on a Java EE problem, you could check which solution comply with Java EE specification better rather than server specification.

From my experience with Jboss and Sun AS, you should just forget about AS-independency.
In sql, for example, you can do quite a lot without employing vendor-specific features. Well, it's not like that in Java EE. For Jboss and SAS even 'hello world' applications will require different configuration. And more application grows, more vendor-specific features you have to use.
In particular, if you look at official Sun Java EE tutorial, you'll find that it employs SAS-specific configuration files (sun-web.xml, sun-ejb-jar.xml, etc) from the very beginning.
But all above applies only if you use full range of Java EE features (like EJB, JMS, mbeans). I've found that if you just have servlets/jsps packaged in one war-archive, such application can still be very portable.

If you have the resources then consider developing and testing for several application servers instead of just your initial target one. This will allow you to - from the start - pinpoint things that need to be configurable and code accordingly.
Personally I would consider Glassfish 3.0.1 in such a situation as it is the reference implementation, so things should at least work there without any special efforts.

Example non-trivial Java EE web service implementation?

My organization is considering switching from an in-house proprietary
application server (and adhoc protocols) to a Java EE 5 / Java EE 6 framework +
web services for new development, and we're trying to get our heads
around how we'd do that.
We're experiencing something of a culture shock; we're comfortable
with emacs/vi, command-line tools, shell scripts and calling libraries;
all the documentation we encounter seems to assume we're using Eclipse,
IDE plugins, ant and/or maven and some huge framework which makes it
hard to even understand what code is executing. I think an example
would help enormously, so my question is:
Is there a modern, non-trivial example Java EE application (or real-world open source application) out there that provides a WS-I style web service interface and ideally also demonstrates using a relational database?
I've found various "hello world" applications and tutorials that
create some sort of web service using a Java EE framework, but never
anything more complicated than a temperature conversion service!

I was in a similar situation a few years ago. I was a C programmer using vi and pico on Linux, and I got hired onto a J2EE project. They may be slightly dated references and there are some differences in the newer versions, but I used the books Developing Web Services with Apache Axis and J2EE 1.4: The Big Picture as great jumping off points for me and the team I was working with. I highly recommend each book. Also check out Sun/Oracle's J2EE tutorial online. Your first iteration won't be production quality code, and should be considered a throwaway from the start, but it will get you off the ground with an IDE and the J2EE framework.

Java EE 6 vs. Spring 3 stack [closed]

As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance.
Closed 11 years ago.
I'm starting a new project now. I have to choose technologies. I need something light, so no EJB or Seam. On the other hand I need JPA (Hibernate or alternative) and JSF with IceFaces.
Do you think that such a stack on Spring 3 deployed on Tomcat is a good choice? Or a Java EE 6 web application could be better? I'm afraid that Java EE 6 is a new technology, not well documented yet. Tomcat seems to be easier to maintain than Glassfish 3.
What's your opinion? Do you have any experiences?

I need something light, so no EJB or Seam.
Would you care to explain what makes EJBs heavy since EJB3? Do you realize that we are not in 2004 anymore? I'd really like to read your definition of light and your arguments (and I will update my answer with pleasure because I'm pretty sure I would have a few solid things to say).
On the other hand I need JPA (Hibernate or alternative) and JSF with IceFaces.
Java EE 6 Web Profile which includes JSF 2.0, JPA 2.0, Bean Validation, EJB 3.1 Lite, CDI,... would be perfect for this and you can use GlassFish v3 Web Profile to run an application built with the Java EE 6 Web Profile.
Do you think that such stack on Spring 3 deployed on Tomcat is a good choice? Or a Java EE 6 web application could be better?
Well, I like the idea to run my code on a non-proprietary platform (Java EE) rather than on a proprietary container (Spring). And I think that Java EE 6 is good enough (and this is an euphemism, EJB 3.1 (Lite), JPA 2.0, JSF 2.0, CDI kick ass). Note that I was a JSF skeptic but I took a second look and JSF 2.0 with CDI is so different that I can't even compare. And if you didn't look at CDI, let me tell you that it rocks.
I'm afraid that Java EE 6 is a new technology, not well documented yet.
Java EE looks pretty well documented to me. This sounds like free claim. And, believe me or not, I start to find Spring getting complicated while Java EE getting easier.
Tomcat seems to be easier to maintain than Glassfish 3.
Did you try something? Did you face any particular problem? Again, this sounds like free claim.

I have not used JavaEE6.
However, I have been beaten up badly enough by all the previous versions of JavaEE and EJB's that I won't trust it until it establishes itself as the de facto standard, not just the de jure standard. Right now, Spring is still the de facto standard.
Fool me once, shame on you. Fool me twice, shame on me. Fool me three times, EJB.
Some will claim that Spring is proprietary. I would argue that the vendor implementations of the JavaEE specs have been just as proprietary, if not more so.
I went through a major conversion recently of moving a bunch of Java Applications from JBoss to Weblogic. All of the Spring/Hibernate apps ported with zero modifications, because they had all the libraries they needed built in. All the apps that used JPA and EJB and JSF were a disaster to port. Subtle differences in interpretations of JPA, EJB, and JSF between appservers caused all kinds of nasty bugs that took forever to fix. Even something as simple as JNDI naming was completely different between AppServers.
Spring is an implementation. JavaEE is a spec. That is a HUGE difference. I would prefer to use a spec IF the spec was 100% air-tight and gave absolutely no wiggle room in the way vendors implement that spec. But the JavaEE spec has never been that. Maybe JavaEE6 is more air-tight? I don't know. The more you can package in your WAR, and the less you depend on AppServer libraries, the more portable your application will be, and that, after all, is the reason I use Java and not Dot-NET.
Even IF the spec was air-tight, it would be nice to be able to upgrade the appserver without having to upgrade all my technology stacks in all my applications along with it. If I want to upgrade from JBoss 4.2 to JBoss 7.0, I have to consider the impact of the newer version of JSF on all of my applications. I don't have to consider the impact on my Spring-MVC (or Struts) applications.

It doesn't matter. Java EE 6 is good enough and because of the profiles there, it is not "heavy" - you'll just be using the web profile.
Personally, I prefer Spring. But I'm running out of rational arguments against Java EE 6 :)
(As I was reminded by a comment - you might want to try RichFaces, as well as ICEfaces and/or PrimeFaces - depending on what components you need).

Recently, one of my client assignments involved evaluating Spring Stack Vs Custom framework stack Vs a Java EE Standards. After a month of evaluation and prototyping, I was not just happy but blown away by the Java EE 6 feature set. For any new "enterprise" project architecture in 2011 and going forward, I would go with Java EE 6 and potential extensions like Seam 3 or the upcoming Apache JSR299 extensions project. Java EE 6 Architecture is streamlined and incorporates best of many open source ideas that have evolved in the last several years.
Consider the following features out of the box: Event Management, Contexts and DI, Interceptors, Decorators, RESTful webservices, integrated testing with embeddable container, Security, and many more.
Most of my results are published in my blog explaining the key concepts of Java EE 6 that you might find useful.
Of course, there is no hard and fast rule for choosing a framework. Java EE 6 could be well bloated for simpler "web sites" that don't require a rich conversational session state. You might as well pick Grails or Play! Framework. But for conversational web applications, I can't see a better argument why Java EE 6 is not a good fit.

Now, after some time, I have experience with stacks :
Java EE 5 + Seam + GraniteDS + Flex
Spring 3 + Vaadin (on GWT)
Spring 3 + JSF 2.0 (PrimeFaces)
My colclusions are:
Spring 3 is much much simpler than Seam (almost Java EE 6) and runs on Tomcat and Jetty! (Jetty for developement with maven plugin is a trasure).
I love Flex (I actually was a Flex developer for long time so I'm biased) and if you need rich interface and can buy FlashBuilder use this, but use this wich Spring + GraniteDS or BlazeDs backend. If you can't buy FlashBuilder don't waste your time.
Vaadin is great!. Developement process is simpler than Flex, but you can create rich application easily without HTML mess. You wont't write a singe JS line. You just need some CSS (in Flex you need it too). So if your application interface is going to behave like desktop application and you can't (or dont want to) use Flex - use Vaadin. Warning! Vaadin has big JS overhead for browser.
If you create simpler website-like application use JSF2.0 (with spring backend as above). You'll need to fight with HTML (I hate it) and creating rich interface will be harder than Vaadin (especially layouts). You will get lightweight HTML for slower browsers/compuetrs. I like PrimeFaces - it's easy and well documented. Second place is IceFaces
If you create a website (NOT a web application) where you need to put life into HTML (instead of create enterprise application that fits into browser) use Wicket (if you prefer component based, pull attitude) or SpringMVC (if you prefer template based, push attitude) or just use Play! framework. Remember that creating rich data-based components will be much much harder but you will have control over each tag of html (your HTML/Graphics designer will love it)

Read Adam Bien's Future Of Enterprise Java ...Is Clear (Java EE with/without Spring and Vice Versa), including comments to get both sides of coin. I will choose Spring for several reasons and following is one of them (reproducing one of the comments from post)
'I am not sure which Java EE 6 server you are talking about. There is Glassfish certified and TMAX JEUS. It will take quite a while (read: years) until Java EE 6 compliant versions of WebSphere, WebLogic, JBoss etc are in production and can be used for real application. Spring 3 just needs Java 1.5 and J2EE 1.4 so can readily be used in almost all environments'

My opinion is based on something not mentioned by others, namely that code at my work tend to live for decades (literaly), and hence that maintenance is very important to us. Maintenance of our own code, and the libraries we use. Our own code we control, but it is in our interest that the libraries we use, are maintained by others in the above mentioned decades or more.
To make a long story short, I have concluded that the best way to achieve this is by using open source implementations of Sun specifications all the way down to the raw JVM.
Of the open source implementations Apache Jakarta has proven to maintain their libraries, and recently Sun has done a lot of work in producing high quality implementations for Glassfish v3. In any case, we also have the source for all modules, so if all else fails, we can maintain them ourselves.
Sun specifications are usually very strict meaning that implementations conforming to the spec can be interchanged easily. Just have a look at servlet containers.
In this particular case, I would suggest having a look at JavaServer Faces simply because it is part of Java EE 6 meaning it will be available and maintained for a very, very long time. Then we have chosen to augment with MyFaces Tomahawk as it gives some useful additions, and it is a jakarta project.
There is nothing wrong with JBoss Seam or others. It is just that their focus is less towards the maintenance issue that is so important to us.

I can see using Spring if you already have it, but for the new project, what's the point? I would go directly with Java EE 6 (ejb3, jsf2.0, etc.)
If the client is fine with Flex, go for it. Use BlazeDS or similar - no mvc. You might spend more time on that part (exchanging data between server and client) but you have full control on both sides.
Don't use Vaadin, unless you want to kill your browser. Plus, you spend more time on getting around the code once your pages become more complex. Also, your mindset will need to be completely changed and anything you know about standard front end development will be waste. The argument that you don't have to use HTML or JS doesn't make much sense. You still have to know it even if you don't use it. It renders to HTML and JS eventually. Then try to debug it - make sure you got few days for simple stuff. Plus, I cannot imagine web developer who doesn't know html/js.
I just don't understand why people are trying all those abstractions instead of using Java EE directly.

Why is there still rumblings about EJB being heavyweight in 2010? It seems people are not being updated in Java EE technologies. Just try it out , you will be pleasantly surprised how things are simplified in Java EE 6.

The answer to your questions depends on your project requirements. If you don't require the Java EE features like message queues, container managed global transactions etc then go with tomcat+spring.
Also from experience I have found that projects that require a lot of web service integration, scheduling, message queues are best best done using some of the Java EE stack.
The good thing is using spring you can still integrate with Java EE modules running in an application server.
Java EE 6 is very different from the previous releases, and it really makes everything lot easier. Java EE 6 combines the best ideas from the diverse Java community - for instance Rod Johnson from Spring framework was actively involved in the making of the Dependency Injection JSR in Java EE 6. A benefit of using Java EE 6 is that you are coding according to a standard, which could be important in some organizations for vendor support etc.
GlassFish v3 supports Java EE 6 and it is quite light-weight and starts up really fast. I have been using glassfish v3 for my developments, and it is really easy to configure. It comes with a very user-friendly admin console that lets you graphically administer your server.
If you are using GlassfishV3 and JSF 2, then you can take advantage of the CDI features of Java EE 6, that lets you easily create conversations (e.g. wizard like pages) in JSF.
Having said that, using Java EE 6 also requires you to learn a new API. Depending on the timeframe available it might not be the best choice for you. Tomcat has been around for ages, and the tomcat+spring combination has been adopted by many web projects, which means lots of documentation/forums are around.

I have worked in both Spring and Java EE 6. What I can say from my experience is that If you are going for the age old JSP or proprietary Flex then you are safe if you stay with Spring.
But if you are to move ahead with JSF then it's time to shift to Java EE 6. With Java EE 6 you are moving to Facelets and standardized script libraries and component libraries. No more script incompatibilities and component library matrices.
Regarding Spring MVC, it's good as long as your project doesn't grow too big. If it's a huge enterprise application stick on to Java EE 6. Because that's the only way you could maintain your own component libraries and resource bundles in an orderly manner.

If you need the Java EE full stack I recommend you GlassFish 3.1. It starts very quickly compared to other Java EE containers which implements some part or all Java EE 6 (JBoss 6, WebLogic 10.3.4), redeployment take seconds and almost all can be done by convention over configuration, it is very friendly.
I you want something "Light" you can customize an Apache Tomcat 7.x with the desired features. I used a lot with the following libraries:
Weld 1.1.0 (CDI)
JPA 2.0 (Hibernate 3.6.x) - only resource local transactions
JSF 2.x (Mojarra)
RichFaces 4.0
BIRT runtime
Been a Java EE developer for the past 10 years (I suffer early EJB, JSF and web technologies), Java EE 6 is very easy, well coupled and current hardware runs smooth so original reasons that motivated Spring are no longer valid.

I'd still prefer Spring.
And I'd pass on JSF. I think it's a dead technology. Spring MVC would be a better alternative. So would Flex. Think in terms of contract first XML services and you can decouple the back end from the UI completely.

I'd recommend Spring + Tomcat unless you can wait the time for glassfish v3 and Weld to become more mature. There are currently a few issues with memory consumption/cpu load when running glassfish with CDI enabled applications.

Didn't read everything but just to tell that you can now use EJB3 inside a war on Java EE 6 so you can use EJB3 on Tomcat (I think).

I recommended to you Tomcat with Spring because:
Spring can create backing beans for JSP
You will use Spring to persist object through JPA
It is good choice to choose Tomcat because you don't need any heavyweight processing