We Keep Coding

What is the advantage of using Direct Web Remoting over a REST web services design?

I have an enterprise Java web application deployed in tomcat.
I am looking for ways to integrate a HTML & JS UI with the mid tier java code. So far, from looking around I have read that there are two ways to do this which fit my requirements :
1) DWR - Direct web remoting
2) Use REST web services.
I am not sure which approach to use.
Edit: What is the advantage of using DWR over a rest WS design?
Is there a better approach available? Some people asked me to have a look at GWT, but I am not sure if these are scalable.
Edit 2: I will most likely be using dojo for the UI development(Works well with REST/DWR??), and I want to keep the java code chages minimal. I understand that by using web services, I would have to write an additional WS client layer on top of the existing java code.
Also, the usual enterprise needs, performance, scalability, etc.

Ok so you're building a web client frontend to your java backend, there are a few ways to go about this:
You want to use java standards as much as possible, preferably living in the java EE world: JSF. You will need some knowledge of HTML, XML and perhaps even javascript (though limited). Personally I have had a pretty buggy experience with JSF+richfaces to the extent that I don't use it anymore.
You are very well acquainted with java desktop application development but don't know much about javascript: vaadin: it allows you to write plain java using desktop application terminology which will be compiled to javascript. Currently I am working on a big vaadin project and it is very nice to be working with pure java in eclipse, the downside is however that you are far removed from the actual frontend, so tweaking can be tricky. Additionally everything is stored in sessions (afaik) and scales poorly.
You are primarily a frontend person with unrivaled javascript skills: use a REST interface in java and a pure js/html/css frontend. Personally I think this is the cleanest design and I have designed a few of my own applications like this. The downside is that managing large javascript projects tends to be hard because...well...javascript sucks. The upside is that this will always be the fastest most lightweight option available to you.
Ideologically I would definitely suggest the last approach but this can be hard for large projects. If you have the hardware to throw at it, vaadin is a nice option. My JSF 2 experience was a bit disappointing due to the bugs in (necessary) third party libraries like richfaces.
PS: I have never heard of DWR but the last stable release seems 2 years old and all it seems to do is expose java code as javascript methods which can be better handled with a REST interface.

Open interface standards like REST and SOAP make it easy to build code to consume these services if you are using frameworks to build a REST Client and a SOAP client code respectively. But the point is that you need to have this client code to make calls to these services.
DWR on the other hand, generates this client code. Your java classes are ready to be called (like you would do in Java).

Migrating/Rewriting a Rails application to Java

Without even attempting to start a flame war between Rails/Ruby and Java guys.
I don't want to discuss why, but I want to rewrite/migrate my existing rails app in Java.
Here are the things that I need to find alternatives for:
PostgreSQL. I can use any DB, but with a capable ORM in Java which is comparable to ActiveRecord.
Resque. For background processing in Rails app. I need to find a similar solution in Java.
MVC. Though strictly not as elegant as Rails MVC, but anything closer to it in Java will be fine.
Any experienced views on this?
EDIT: I want to develop in Java language (so this rules out Scala,Groovy, JRuby and similar languages)

I was developing web applications in Java for about 8 years before I switched to Ruby/RoR. A standard set of libraries that I would recommend is:
Spring MVC
Hibernate ORM
maybe Quartz as a Sidekiq equivalent
Spring ROO to tie it all together and bootstrap things
I would recommend freemarker or velocity as a replacement for JSP.
But whatever you choose, you will regret it :)

ORM: Hibernate is pretty much the standard. Any which implements JPA would do, though.
Background processing: Often provided by your app server (e.g. JBoss).

The JavaLite stack is the closest thing to Rails in Java, complete with ActiveWeb (web part - controllers, testing, dynamic compilation, custom tags, etc.). ActiveJDBC - ActiveRecord implementation, DB-Migrator for migrations: http://javalite.io/database_migrations, HornetNest ( JMS - based command pattern replacing Sidekiq), and a lot more. Entire stack for modern Java Web development in one package.
Check out: http://javalite.io

Lift framework with java

I'm building a web application that needs high performance. I intended using Java EE but after researching about it, there are many negative comments about Java EE applications.
I'm thinking about the Lift framework, but it seems that Lift only support Scala, and I only know Java. Does Lift actually support Java? (I can't find any project example that uses Lift with java). I downloaded a Lift framework project application and there is a boot file in it, can we create a same boot file but for Java?

I'm pretty sure Lift is Scala only. If you're looking for high performance and Java then you should check out the Play Framework as it also has the benefit of not requiring a Servlet container to be deployed.

The Lift framework is Scala only. I want to note that in my experience the transition from Java to Scala was not that hard and now that I know it, there are many language features that make development easier and faster for me. You can take a look at this guide for transitioning between languages: http://www.scala-lang.org/node/960 to see if it might be something that might be right for you. From experience, I really enjoy using the Lift framework as it offers a lot of performance and functionality. The documentation is a bit lacking, but the community is great and makes up for that if you get stuck.
As for Java EE having negative comments, that is a bit vague. The Java EE spec includes everything from Servlets to JSF and EJB. Parts of the spec you will find in almost any web framework (including Lift) and others are more specialized. JSF for example has a lot of overhead, but tries to simplify a lot of the typical application lifecycle. EJB similarly tries to simplify the persistence layer through object relationship management (ORM).
High performance sites can be accomplished with most frameworks, but a lot of it will come down how you develop it. Also, because the framework supports it does not mean you need to use a particular component. Spring (http://www.springsource.org/) is a framework that many people have used on high performance sites, and is incredibly configurable (Supports EJB and JSF, but you don't need to use it). Also, Wicket (http://wicket.apache.org/) is a Java framework that offers a similar feel to Lift that might be interesting to you.

I worked with Lift only for a year now, and was never really interested if it would run from java (I wanted to learn new effective conceptions anyway).
So, I don't fully know the subject. But what I know for sure is that Liftweb has java methods almost everywhere to support java, too. So, you can build your app if not fully in java, then most part of it.
Prooflinks are like these:
http://main.scala-tools.org/mvnsites/liftweb-2.4-M4/net/liftweb/actor/LiftActorJ.html
Classes that add support for java by adding java-acceptable method names and such. These classes usually have a "J" letter at the end.
Anyway, I'd suggest to try out Scala, too -- it's great. And even if you use java only -- you probably will get used to Scala anyway, because you probably would want to read the source code sometimes.

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.

Can I avoid Java EE to create a light-weight web page?

Everything I download seems hellbent on using all of Java EE. I need to build a single page to handle requests to it and do a tiny bit of processing based on parameters. This is to hook into another framework that will routinely call this URL.
I want a quick and easy way to create a page with some processing. Is there an easy way to do this using Java? I am using Java because I am comfortable with Java. I used SE for years and did some work in EE but I don't want all the stuff that comes with EE.
Should I maybe just avoid Java altogether and use something else. This needs to be deployed in a linux environment.

I used SE for years and did some work in EE but I don't want all the stuff that comes with EE.
Then just use a Servlet and that's all. Nothing, I repeat NOTHING, forces you to use "all that stuff" and your question is either a free rant or shows some deep misunderstanding.

You need Tomcat (or jetty, or any servlet container - jetty has an embeddable version btw)
You need a .jsp file and optionally an HttpServlet
Generally, it's not a good practice to put any processing code in a JSP, but if it is really simple and won't be extended, simply put the logic there - it is translated to a Servlet anyway.

yes, all the servlet based solutions are quite chubby.
jetty is all right, but the download is 20MB. that is ridiculous.
currently, the best choice is probably com.sun.net.httpserver which is bundled in JDK 6. you can easily implement your service.

It sounds like you could use PHP to do your processing. Call the page and POST the parameters to it, compute, and return the result.

If you are not very particular about using java and are willing to experiment, you should look at nodejs. It runs on V8 javascript engine and runs on linux.
There are a couple of fraemworks for nodejs for web apps:
Expressjs and spludo

as mentioned, you can do this very simply with jetty and a servlet, you don't even need a JSP if you just need a URL that does some processing based on request parameters and returns a response.
For development, it's really easy to create a dynamic web project in eclipse, just follow the steps in this article.
That said, I don't think java is a great choice for really lightweight stuff. PHP is probably the easiest thing to use if you just want to get it working yesterday.

You can use Java with FastCGI. This is very flexible, but also a bit low-level for most Java programmers.
If you aren't afraid of servlets (they are only a very small part of Java EE!), I can recommend JAX-RS, it is quite easy to get started with. If you client-side is JavaScript based, you can avoid using JSP (which I would recommend you to avoid).
For example, see backbone-jax-cellar. The Java source is here. For a Java app, this is light-weight. He is rolling his own DAO, but that's the price you pay for using Java and SQL and no dependencies (other than JDBC). The code is reminiscent of object-oriented PHP if you ask me. The point is, that if you have a JavaScript client, you don't need template rendering or all that cruft and a REST interface should be enough.
If you are afraid of the heavy build systems too, I made an example REST Todo app backend (which uses an existing frontend) that only requires a POSIX system, the JDK and sqlite3, and gets its own other dependencies (including webserver). I did not use a DAO. The repository front page has a README.
Another possibility is the Play Framework which does not use Java EE. It is rather heavy-weight, though. Full featured though. You would definitely need to use an IDE for this, you don't need that for developing JAX-RS/FastCGI apps.

I would reccomend Sinatra it is a very light-weight ruby web framework.