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Current core technologies for AJAX w/ Java?

Looking to implement a RIA using AJAX with Java on the backend.
I was looking at DWR for an RPC style approach, but the project hasn't been updated since 2008.
I was also looking at DOJO and GWT.
Can anyone recommend a core set of technologies that works best for a Java based back end, that contains a rich set of client side widgets and backend integration with Spring WebFlow/MVC?
thanks

I would recommend Spring 3.0. It's up to date, lightweight, easily configurable, supports dependency injection, annotated classes, and is a great framework.
It supports REST, so it's easy to implement classes that return JSON to your HTML pages. This will help keep your content, behavior, and presentation all separate while still enabling you to build a Rich Internet Application.
Although outside the scope of your question, I'd suggest you use JQuery on the frontend as I've had really good results using it to transfer JSON back and forth from the server.
I would stay away from DWR. They merged with Dojo, which in my opinion is a better choice than DWR. DWR sounded good, but in practice it was buggy and difficult to use. Dojo was much cleaner and more modular. But unless you're using Comet (aka Reverse Ajax) just stick with Spring and JQuery.
Spring 3.0 is also supported on Google App Engine... just worth mentioning as Platform as a Service is in our future.

My recommendation is a RIA framework like SmartClient or ExtJS + a REST-based backend (built on Jersey, for example). I have also found JQuery to be extremely helpful when combined with these frameworks. Together. this allows you to build your GUI right on top of a REST API, which itself could be reusable for programmatic integration.
These kinds of questions are always religious ones, but FWIW I am personally not a massive fan of GWT, for multiple reasons. One of those reasons is because I don't want server side folks constructing GUI-targeted data structures (I'd rather have them stick to pure data and let me GUI folks handle the GUI stuff). So I actually don't appreciate that capability of GWT, but obviously many other people welcome that aspect, so again it's a religious choice.

you can try GWT.That supports Spring well.
http://www.springbyexample.org/examples/simple-gwt-spring-webapp.html

If you use a Spring MVC back end, you can use any AJAX frontend there is.
And if you are going to develop a RIA, I would suggest either Prototype with Script.Aculo.Us (Killer GUI effect library) or MooTools (which is either an extension or a re-write of prototype, that also includes many GUI tools).
The great thing about both ProtoType and Mootools is their Object-Oriented methodology (MooTools Class() docs, Prototype Class.create() docs), but the extension mechanism that gives additional methods and properties to DOM elements (How Prototype extends the DOM, MooTools Element reference). Of course this mechanism is exactly what the JQuery guys loathe about these libraries. But the nice thing is that because of these extensions, you hardly ever have to resort to browser-specific programming, the abstraction handles that for you.

I choose JSF for RIA applications.
It is J2EE 6 standard
it built-in in J2EE application servers (glassfish, jboss),
it has several implementations - if you have problem with one, you can switch to another
I has at least 4 (richfaces, myfaces, icefaces, primefaces) independent, big components libraries.

Spring can work well, but my personal preference is for simplicity, and Spring is bit heavy platform. So I prefer deploying services on JAX-RS containers (like Jersey); Guice for wiring things together, and in case I want to override or change data bindings, Jackson for JSON handling.
Other useful pieces would be jDBI for database access (much simpler than hibernate or other full ORMs), async-httpclient for doing calls to other web services.
Best of all, these all work nicely for many other kinds of uses.

WHich is the best path or flow to learn java from web site perspective

I have just started learning java and i have about 8 months time. My main aim is to build web application using java. But as there are many java technologies/frameworks available i am conufused how should i go
IDE i am using is eclipse
The path which i am thinking is below
1)Learn Core Java
2)Project: Build Java Invoicing System with JDBC or mysql to test java knowledge
3)Learn Servlets / JSP to
4)Build small site like simple logon/memberarea/catalogue using servlets/jsp
Now guys I really don't know where the following things stand in my path and which things they will help
1)Java EE
2)Spring or spring MVC, what's the difference?
3)Hibernate
4)Wicket
5)Struts
I really don't know how should i learn those and which things to choose from.
what should be my final project which can be build using those because if i see from my current stage even website can be build using servlets/jsp. then why do i need those other technologies
Can anyone give an example of a project which can be build using new technologies and not using jsp/servlet, so that I can get an idea why we need those?

Lot's of stuff to learn in here so I would take it a bit at a time. I'm going to assume you are relatively comfortable with the Java language and core APIs.
First learn about JDBC and databases. Get a basic functional JDBC example app working (not visual just some a vanilla Java app) that does read/insert/update/delete of some records in a table. This will give you the basis for building whatever app you choose. Almost all interesting applications involve some sort of persistence/database.
Learn the main JDBC APIs (Connection, PreparedStatement, ResultSet) and write some code that uses these to get comfortable.
Learn about how transactions work in databases if you aren't familiar already and how JDBC uses them (Connection.commit and rollback)
Next you could look into the spring framework. This has a several useful features that come in handy when building these applications. The main ones to get to know the dependency injection functionality and the JDBC libraries it has. The DI stuff is a bit of a "duh"? if you haven't used it before but it is very useful/powerful especially for medium size + apps. The JDBC libraries help with the cruft of dealing with the raw JDBC APIs and make your code less error-prone.
Once you've got some basic JDBC and Spring stuff worked out you can then start bringing in a web framework.
This is more difficult because there are so many. In the interest of getting something up and running quickly I would probably go with Wicket. It runs inside a servlet container like Jetty, easy to get up and running with a basic web page or two and relatively easy to evolve of the project over time without going down too many blind alleys. I've found that frameworks like JSF (the Java EE default web/view framework) takes a lot of up front time investment to get going on. Most of these frameworks, including Wicket, can leverage the spring stuff you've got above.
Avoid JSP, it's unpleasent technology and outdated by virtually everything else.
To answer some of your other points.
Hibernate is a tool for mapping an object model to a relational model. In it's most basic form you define a Java class for each DB table with the class having one Java property (variable+getter+setter) for each DB column. You can also add references from one class to another to model database relations. It is good but it takes a bit of getting used to.
Spring I've explained partly above. Spring is much bigger than just DI and some JDBC libraries. It also has transaction management libs and bunch of other stuff. Spring MVC is a web framework which lives under the spring umbrella and makes use of a lot of the spring libraries internally. I've never used it so can't offer an opinion on it.
Java EE is an umbrella term for a large set of "enterprise" specifications/libraries. JSF is a web view framework that is part of Java EE.
That's my very high level advice. To summarise I would learn basic DB/JDBC then some spring stuff and then start building a basic web app using what you've learned already.
Hope that helps. There's plenty of info out there on the web on all these topics and you can always ask questions here on more specific parts if you need help. Good luck and enjoy!
EDIT (to address comment):
All of the above is my recommendation/opinion on how to approach learning Java web development.
In summary
Learning JDBC/transactions/databases is a must
Spring is optional but I strongly recommend. Spring is a big library but you can pick and choose the bits you like/need.
Web frameworks the choice is really yours. From what I have tried (JSF/JSP/Wicket) Wicket is the easiest to get going with so you don't spend too much time frustrated with the getting the initial setup. JSP is awful, it's very easy to make a mess with it. JSF is powerful but heavy and probably more suited to very enterprisy projects than a first web app.
Hibernate is optional but can make life easier simply because you can work with Java objects when you do DB queries/updates rather than writing tedious insert/update statements. Hibernate isn't the only tool like this but it's the one I've used most and does the job well. Just don't go too overboard with the "clever" hibernate features initially.
You could easily use Spring MVC instead of Wicket. That may be a perfectly good choice, I've not used Spring MVC myself so can't comment. I'm sure it will integrate well with spring stuff tho so that would certainly be a positive factor.
Do some more research if you're not sure, there's no end of people happy to give their opinion! But really you just have to dive in and try something.

You are correct. If all your applications are served by servlets, JSPs, and JDBC, then maybe you don't need to learn anything else.
I commend you for learning the fundamentals first before diving into a thicket of frameworks that you don't understand. That's a good thing.
But if you reach the point where you have those down cold, maybe looking at these other technologies can help you improve your game.
1)Java EE
You are learning (part) of Java EE when you use servlets, JSPs, and JDBC. They're a subset of the full Java EE machinery - EJBs, JMS, JNDI, etc.
2)Spring or spring MVC whats
difference
Spring is an alternative framework developed by Rod Johnson and Springsource, now part of VMWare, that is based on dependency injection, aspect-oriented programming, and framework modules. Spring web MVC is one module in the Spring framework, based on servlets, that acts as the front end for web applications.
3)Hibernate
An object-relational mapping technology (ORM), built on top of SQL and JDBC, that lets you map objects to tables. It has its own object-based query language.
4)Wicket
Another web MVC alternative to Spring MVC, Struts, JSF, etc.
5)Struts
The first web MVC framework. It's gone through versions 1.0 and 2.0, and has now been supplated by Java Server Faces. It's still used, though. Like all other web MVC frameworks in Java, it's based on servlets and JSPs.

From a Java perspective it might be best to start looking at Java EE. All the others you mentioned are alternative technologies, which might be useful to you if you decide that what the standard framework offers isn't your cup of tea. But for that to decide, it's never a bad idea to at least know what the standard framework is about.
Truth be told, before 2006 the standard framework had a bad reputation and some of the sentiments that form the basis for recommending alternative technologies are still based on that. Starting with version 5, Java EE got dramatically better. The latest version, Java EE 6 is arguably one of the best Java frameworks that's out there. Of course, the best is a highly subjective term and naturally it won't be the best one for each and every person out there.
At any length, Java EE 6 is a very complete framework that allows a large range of application to be written without depending on any additional library. Being the standard framework, most other frameworks at least depend on some parts of it.
Most typically EJB, CDI and JSF are replaced by alternative technologies. E.g. the core Spring container replaces EJB and CDI and Spring MVC replaces JSF. A full Spring stack typically still uses JPA, JTA, JMS and Servlet from Java EE. Wicket on its turn only replaces JSF, or when used with a Spring stack replaces Spring MVC.
Hibernate is a special case. It doesn't replace anything from Java EE, but is instead often used as an implementation for one of the key APIs of Java EE: JPA. The original creator of Hibernate, Gavin King, is one of the prime supporters of the Java EE framework and is in fact the spec lead of one of the most important parts of modern Java EE: CDI.
Wicket by itself is a very nice web framework, but in practice it isn't used as often as JSF. I won't go into the discussion whether Wicket or JSF is 'better' (this is mostly a religious battle anyway), but due to the popularity of JSF there are simply more people experienced with it and there is a large community offering many things for JSF like component libraries and extensions.
Struts has historically been completely replaced by JSF. The original creator or Struts, Craig Mcclanahan, was the one who started JSF as the successor of Struts. Nevertheless, Struts was once the absolute de-facto standard for web frameworks in Java. It's not often advised to be used for new projects, but till this day it's still used in a huge number of existing applications. So even though it's not really 'hot' to learn Struts anno 2011 knowledge of it may still be very practical for when you have to maintain existing applications.
ps
See this answer for a general description about Java EE: Frameworks for Layering reusable Architectures

I'm sure that nobody seriously can tell you the best way, because this would mean that (s)he would have tried all. Why do you want to learn a Java web application framework? Just to learn it to be prepared for the (next) job? In that case it is likely that you've learned the wrong one.
The next question would be what you want to do with the web application framework. Do you want to make a website a little bit active, e.g. make each page look similar (corporate design), auto-generate menus from an internal structure, or do you want to write a real web application, e.g. with database access.
I'd first define the goal what you want to achieve. IMHO a good way to motivate you to make it right is to take a small project which helps you to solve a small problem.
Then I would start with Java Server Pages (JSP) and servlets to understand the basic concepts. Then you can try to do the same with a few well-known web application frameworks, e.g. Wicket.

Which Java based MVC framework is most similar to ASP.NET MVC?

I have been learning ASP.NET MVC in the last few months and I think it is a great improvement over ASP.NET. For me personally, it is a joy to use (as opposed to ASP.NET WebForms :)) I started wondering how the .NET world managed to live so long without any such framework (at least not wide spread and supported by Microsoft as there may be .NET ports of Java MVC frameworks, like Spring.NET).
I know Java folks had such frameworks for a long time and there are many Java MVC frameworks available.
If a web developer was thinking about switching from Java to .NET, which Java framework can be the easiest to switch from, and vice versa, if an ASP.NET MVC developer is thinking about broadening his skillset and learning some Java MVC (web) framework, which would be most similar to ASP.NET MVC architecture- and feature- wise?
Which Java MVC framework is most similar to ASP.NET MVC?

SpringMVC, VRaptor, Grails (Not Java, but somewhat relevant on the Java world)

Play Framework seems to me. It has controllers as classes, actions as methods, Razor-like view engine, object binders and almost everything looks the same.
Even routing seems almost the same.

If I were looking for the simplest framework, I'd dive into Struts. Struts 1.0 was written in a day, and is possibly the most valuable hour-per-hour effort ever spent by a programmer.
If I were looking to broaden my knowledge and/or skills, I might lean towards Spring MVC. If you need some functionality for Java web development, odds are other people wanted it too, and that Spring already has it. (Spring is larger than just Spring MVC; you can simply use Spring MVC, but it integrates nicely with much more, if you choose.)

Wikipedia has a list of a bunch of frameworks here:
http://en.wikipedia.org/wiki/Comparison_of_web_application_frameworks
and of those based on Java technology, about half are component based (that's what you don't want) and the other half MVC. If interested, you could follow the links on some of those to get more information.
In general,
the more mature of them will have more detailed writeups - both in Wikipedia and in the wild. There will also be more documentation, sample code, tutorials,...
The younger ones may be simpler, more fun, more versatile, as they build on the older ones, eliminate known shortcomings and add new features. JSF and Struts, for instance, are "big" in the industry but are considered by many developers (citation needed, I know) to be dated, clumsy, bloated, etc.
You'll probably have trouble getting an answer from people with enough experience to directly compare products on the .Net and Java side; most developers tend to stay on one side of that fence.
While I'm not knowledgeable about similarities with ASP.Net, I submit that Struts and JSF are the workhorses of industry on the Java side, and would be the kind of thing to be useful to have in your CV, even though or perhaps because they're not modern or sexy. Of those two, I think Struts has more of an MVC feel to it.

Apache Struts :
Apache Struts is a free open-source framework for creating Java web applications.
Web applications differ from conventional websites in that web applications can create a dynamic response. Many websites deliver only static pages. A web application can interact with databases and business logic engines to customize a response.
Web applications based on JavaServer Pages sometimes commingle database code, page design code, and control flow code. In practice, we find that unless these concerns are separated, larger applications become difficult to maintain.
One way to separate concerns in a software application is to use a Model-View-Controller (MVC) architecture. The Model represents the business or database code, the View represents the page design code, and the Controller represents the navigational code. The Struts framework is designed to help developers create web applications that utilize a MVC architecture.
The framework provides three key components:
A "request" handler provided by the application developer that is mapped to a standard URI.
A "response" handler that transfers control to another resource which completes the response.
A tag library that helps developers create interactive form-based applications with server pages.
The framework's architecture and tags are buzzword compliant. Struts works well with conventional REST applications and with nouveau technologies like SOAP and AJAX.

is struts a good starting point for java web

I've been developing in java then I stopped, so now since I have my google app engine account I wanted to start with this again. Also, I love web and I know struts is a good MVC framework.
I've been reading this. Do you think struts can help me to start or should I start with "plain" servlets, and then go to some framework?

I would at least learn the basic servlet lifecycle and API.
As Joel puts it abstractions are leaky and this applies to frameworks--all frameworks not just Web ones--equally well. You will be much better equipped to use a framework, to know why it's good and how it can help you if you understand the underlying technology, the thing it is trying to abstract.
As for Struts, I would steer clear of STruts 1. It's rather ancient now. There's still a lot of code around for it but I wouldn't consider it best practice now, particularly for its (over)use of inheritance. Struts 2 is really a completely different framework based on Webwork.
There are plenty of other MVC frameworks out there. Personally I like Spring MVC as being quite "pure" and lightweight.

I'd definitely start with an MVC framework as opposed to "plain" servlets as you suggest.
While I've used Struts 1.x a lot, I think for a new application you should look at Struts 2, Spring MVC or some other newer framework that leverage new Java features such as annotations.

I completely agree with cletus in the sense that I would start by completely understanding Servlet/JSP first.
After that, I would go to a more modern framework than Struts. To me, JSF or Spring sound like better options than Struts these days.

Struts 1 is now obsolete and Struts 2 doesn't seem to be getting much traction. There are lots of good frameworks out there, and you may want to consider instead: JSF, GWT, or Spring for example.

I suggest you to use Struts 1.x rather than Servlet, because this gives you lot of benefits like
PageNavigatin
Input validation
Extensibility
Modularity

I too agree in that learning fundamentals (Servlet API is a must, jsp/jstl highly recommended) first is the best thing to do. And for many simple things jsp/jstl combo is actually plenty good. But bigger the system, less maintainable such web apps tend to become. This is inverse of using heavy frameworks like JSF.
Beyond ones already suggested, I would recommend checking out Tapestry and Wicket: many developers like them. My experiences with JSF have been bit negative; but it's one of those love-or-hate frameworks, many swear by it, others just swear at it.

Technologies required to build an end to end web application?

I want to develop a web application, like an online scheduler. (Yes I know it's been done a million times.)
Most of my experience is in Java, so I want to leverage that when considering technologies.
I've primarily been a systems developer with little exposure to UI programming, so I think this is where I will need to do most of my learning.
Do you have any suggestions on the technologies I should focus on? I want to focus on technologies that are marketable and easy to learn.
So far this is what I think I need for a 3-tier architecture (from the ground up):
Database (likely MySQL or PostgreSQL) - SQL, JDBC
Back end server - Java
Web server (Tomcat) - JSP, Servlets
Web Framework - Tapestry (weak on this, any better alternatives?)
Browser technologies - HTML, Javascript, CSS (need to learn)
I've heard about "Rich internet application" development tools such as Flex and Silverlight, but I'm not sure about the market for such technologies.
Edit: Seems like there's a lot of mention of Spring/Hibernate, so I'll look into that. I appreciate the feedback.

I think you've got your bases covered pretty well.
You'll probably want to look into some frameworks / libraries to make it easier on you.
Web Framework - Wicket / Stripes / JSF / Tapestry (component vs request based frameworks)
Javascript Library - JQuery / YUI / Dojo
As for your template language you could use JSP / Velocity / Freemarker.
Just study up on the frameworks and tools maybe try a few out and see which ones work best for you.
Just FYI I'm currently using.
Apache - web server
Tomcat - servlet container
MySQL - database
Stripes - request based web framework
YUI - for ajax
Spring - dependency injection
Hibernate - Object Relational Mapping
jsp - to dynamically generate html

I'd personally add Spring to this list. Dependency injection is definitely a great technology to learn, and Spring lets you use it as much or as little as you like, in my experience.
You haven't explicitly mentioned unit testing, but that should certainly be part of the mix - I don't have much experience outside JUnit as an actual testing framework, but there's also EasyMock and JMock (amongst others) for mocking of dependencies.
None of that's web-specific, but still important stuff IMO :)

I would have to disagree that there isn't a market for Rich Internet Application. There is actually a growing trend in enterprise size applications being made as RIAs. The advantage with RIA over normal web applications is usability. You get all the advantages of web application but still are able to keep the desktop-like user interface.
You say you come from a Java background and haven't had much experience with web technologies. Well, I have to say that you really sound like an ideal user candidate for either GWT or IT Mill Toolkit (based on GWT). Both are frameworks which allow you to create rich internet applications purely in Java! No HTML or JavaScript skills required. You will have to learn CSS to make your own theme for the application.
Both the frameworks are open source and suite very well for commercial use. What separates IT Mill Toolkit from GWT, is that it is server driven, meaning business logic is implemented and ran on the server rather than as JavaScript in the client browser (which is the case with GWT). This server-driven architecture makes the application much safer from a software security point of view. The advantage of GWT over IT Mill Toolkit is the larger user community.
What comes to the ORM frameworks, Hibernate is quite popular. However, I'm not very fond of it, because even though it technically implements Java Persistence API, it doesn't always behave as expected and you'll have to use a lot of hibernate specific annotations, which ties your application pretty hard to hibernate (bad thing!) and you cannot just easily swich to another JPA provider if you'd like to. Antoher ORM framework implementing the JPA is EclipseLink. I haven't personally used EclipseLink in enterprise size applications (because I still haven't had the chance to), but I'm using it for a smaller project and it seems to be quite nice. EclipseLink is open source and its lisencing is friendly for commercial use. EclipseLink is continually developed by Oracle, so its backgrounds are solid. It is actually based on TopLink, which is Oracle's closed source JPA implementation.
Hope this helps :)

Asked basically the same question some time ago, with some pretty useful answers:
Tools for website development

If you are going the with a Java back-end, I would recommend Hibernate for your JPA, JSF with RichFaces (AJAX/skinning) and Facelets (view rendering/templating) for your front-end, and Seam to put it all together. It's a wonderful combination.

If you go with Spring, then you may just use Hibernate going to mysql, and you can have everything you need there.
After you write it, and you want to start improving on it, then perhaps start looking at doing more on the browser side, but, initially, you may want to just have it be without ajax calls.
The Spring Framework documentation may be helpful, as there are many parts to Spring that you can use, optionally, such as Spring MVC, Spring Framework, Spring Webflow and Spring Security, if needed.