What are the differences using spring boot with Kotlin and with Java?
Kotlin is among the three languages you could choose to start your app with https://start.spring.io. So it's supported by the spring boot team. I used it to develop some microservices and as far as I know everything went fine at the end but I would like to have some feedback from other developers because I try to convince my new team to start our new microservices in Kotlin.
Pros:
Null safety
Clearer code
Val over var
Cons:
Mockito not Kotlin friendly (I switched to mockk)
Code coverage was not out of the box (we had to develop our own plugin)
Risk to have Java moving faster than Kotlin
Since Kotlin is simply a dependency and plugin for Maven (that's it!). It's such a nice, compact, easy-to-grok language that removes all the syntactic fat (opposed to syntactic sugar) that Java provides.
From 5.0.0 onward Kotlin has first-class support from Spring, which effectively means it has all the same guarantees as Java in terms of code working correctly.
Kotlin itself has a ton of interoperability features to smoothly integrate with any already existing Java library, which means you have the same freedom of choice.
Kotlin's Java interop is amazing, and was by no means an afterthought by Jet Brains. Thus Kotlin works nicely with Spring, which provides a lot of the boilerplate functionality for web applications, especially Spring Boot.
These are some points which You already mentioned but I will still have a say about it. Kotlin has a much more compact syntax and its type system allows for much more robust code through null-safety, sealed classes, and immutable/mutable collection distinction, which together significantly reduce development time on any project.
The main difference is: with Kotlin, you're programming in Kotlin...with Java, you're programming in Java. Spring makes use of some languages features exclusive to Kotlin to streamline certain operations, but I wouldn't think you'd want to choose one language over the other just because of those few additional benefits. For the most part, there is no difference. Spring supports both languages well.
UPDATE: I guess I should add that Kotlin does introduce a few minor problems into the whole Spring thing, just because Spring is actually written in Java and was originally designed to be utilized via Java. But just like the pros you get with Spring and Kotlin, these minor negatives should likewise not dictate your choice as to which language to use.
I think what you should be asking is "which language should I use leaving Spring out of it?". My company is coding new modules in Kotlin because we consider it a significantly better language than Java. But we have lots of legacy Java code, and we've chosen to for the most part not mix languages within a single module, so we still code in Java too. You have to make your own decision. Decide what language you want to program in based on the language itself, and on your existing codebase, but not on how Spring works with it. Spring will work great with either.
There are many articles and blogs out there comparing the two languages, listing their relative pros and cons. I'd suggest that you read everything you can. There's no "right" answer here. (...which is why I know this question is going to be closed as being opinion-based). Try Kotlin. Heck, try Groovy and Scala too. "live" the pros and cons for yourself, and then decide what will work best for you.
BTW, you list "Risk to have Java moving faster than Kotlin" as a Con of Kotlin. I think the risk is in the other direction. Java moves very slowly compared to Kotlin and other alternative languages. That's why you see it playing catch-up...finally introducing features into the language that have been in the alternative languages for many years.
I'm currently evaluating QI4J, as it provides interesting concepts regarding properties handling, in the context of an application connecting some ontologies together to create a partially semantic application.
As a consequence, I would like to find some alternatives regarding properties handling, composition, and integration in Java EE environment.
The most obvious similar thing to Qi4j, I think, is Scala. However, it is a new language and all the good and bad things that comes with that.
For Qi4j, we are aiming for strong Scala support, so that for instance Scala traits can be used in Qi4j composites.
According to Ohloh page of QI4J, possible alternatives are
Indriagen
javATE
learn-ddd
zipper-framework
I think you can do most of what Qi4j does (and way way more) with AspectJ ITDs (the language not the #AspectJ Java alternative).
Jordao mentions it in his answer to the similar post mentiond by #Ischin.
Here is an example of trait-like functionality I mentioned in another post: https://stackoverflow.com/a/7403617/318174 . Just by adding an interface to a class you can magically add methods.
A legacy web application written using PHP and utilizing MySql database needs to be rewritten completely. However, the existing database structure must not be changed at all.
I'm looking for suggestions on which framework would be most suitable for this task? Language candidates are Python, PHP, Ruby and Java.
According to many sources it might be challenging to utilize rails effectively with existing database. Also I have not found a way to automatically generate models out of the database.
With Django it's very easy to generate models automatically. However I'd appreciate first hand experience on its suitability to work with legacy DBs. The database in question contains all kinds of primary keys, including lots of composite keys.
Also I appreciate suggestions of other frameworks worth considering.
Use sqlalchemy. On any framework you choose. It can reflect your database as ORM.
I’m currently rebuilding a legacy PHP web application with a MySQL database my self.
The PHP code was kind of spaghetti and is now rewritten in Java as it type safe, promotes well-structured code, has excellent tooling and has superior unit testing capabilities. For database to Java mapping I use Hibernate/JPA.
The web application is incrementally delivered to production. Meaning we run both Java and large parts of the old PHP code together until the application is fully converted.
But in order to use hibernate effectively we needs the database to be logical correct (something MySQL MyIsam does not enforce). So with each production release I run an refactoring scripts for the database (also used to build the development environment and do unit testing) and update the PHP code with a new version that works with the schema changes.
As a web framework I use Stripes as it’s simple, elegant and easy to learn.
I have very good experience with Django. Every time I needed it was up to the task for interfacing with existing database.
Autogenerated models are the start, as MySQL is not the strictest with its schema. Not that it will not work only that usually some of the db restrictions are held in app itself.
My first thought would be to use Hibernate and Java, but I may be biased because that is what my experience is in. You generally map your Model classes via Hibernate after you create the database anyway, so it might not be a bad choice.
I'll let it explain itself to you: Hibernate's website
I suppose that any PHP Framework (I'm a PHP guy, so I will only talk about PHP) could be OK for you ; but you should use one that's well-supported, has a large community, ...
To make things short, I'm thinking about one off this list :
Symfony
Zend Framework
CakePHP
Kohana
Code Igniter
Now, if you're asking "which framework is the best", it's a question that doesn't really have an answer : it's mainly a matter of personnal preferences...
Still, here's a couple of questions+answers that could bring you some interesting informations :
Best PHP framework for an experienced PHP developer?
What PHP framework would you choose for a new application and why?
To use a PHP framework or not?
PHP Framework Decision - Analysis paralysis!
PHP - MVC framework?
Which PHP Framework is right for this project?
Also, note that choosing a Framework is an important decision -- which means you should take some time to evaluate each framework and how it'll answer your specific need.
Really : you should definitely not rush that decision.
You know, there's a whole Ruby web dev world away from Rails, e.g.:
Sinatra
Ramaze
Webby
With such a general question it's always a bit hard to help...
Try web2py, extremely easy to prototype any webapp, and IMO a bit easier to grasp (overall) than other similar web frameworks, HTH
There are no clear cut winners when picking a web framework. Each platform you mentioned has its benefits and drawbacks (cost of hardware, professional support, community support, etc.). Depending on your time table, project requirements, and available hardware resources you are probably going to need some different answers.Personally, I would start your investigation with a platform where you and your team are most experienced.
Like many of the other posters I can only speak to what I'm actively using now, and in my case it is Java. If Java seems to match your projects requirements, you probably want to go with one of the newer frameworks with an active community. Currently Spring Web MVC, Struts2, and Stripes seem to be fairly popular. These frameworks are mostly, if not totally, independent of the persistence layer, but all integrate well with technologies like hibernate and jpa; although you have to do most, if not all, of the wiring yourself.
If you want to take the Java road there are also pre-built application stacks that take care of most of wiring issues for you. For an example you might want to look at Matt Raible's AppFuse. He has built an extensible starter application with many permutations of popular java technologies.
If you are interested in the JVM as a platform, you may also want to look at complete stack solutions like Grails, or tools that help you build your stack quickly like Spring Roo.
Almost all of the full stack solutions I've seen allow for integration with a legacy database schema. As long as your database is well designed, you should be able to map your tables. The mention of composite keys kind of scares me, but depending on your persistence technology this may or may not be an issue. Hibernate in Java/.NET supports mapping to composite keys, as does GORM in grails (built on hibernate). In almost all cases these mappings are discouraged, but people who build persistence frameworks know you can't always scorch earth and completely recreate your model.
I'd like to know how you address the seemingly low productivity of Java EE-based web application development compared to other technology stacks (Seaside, Ruby on Rails, etc).
The constraints are:
The finished web application must be deployable on Java EE compliant application containers
If possible, previous investment in Java-based solution should be preserved, i.e. native interoperability with Java-based systems and libraries should be possible
Due to team structure, Java as implementation language is preferred, although less exotic JVM-based languages (i.e. Groovy) might be acceptable as well
The resulting system needs to be architecturally sound
The resulting system needs to be extensible and maintainable
To not let this dwindle into a philosophical discussion, I'm only interested in suggestions that are based on practical experience. Possible examples include domain specific languages, frameworks and MDSD.
If you point to an abstract class of solutions (like MDA / MDSD), please provide details on how you implemented it as well as information about common pitfalls and best practices.
If you disagree on the assumption that Java EE-based web application development implies inferior productivity, I'd like to hear your reasoning as well.
EDIT:
As there are a lot less answers than I expected, I'll accept accounts of abortive attempts as well, basically extending the question to "How (not) to improve productivity when developing Java EE based web applications?".
I believe the Java EE Java stack is actually very good. There are a few reasons explaining the low productivity of Java EE:
Being “the enterprise stack”, it is often used to create boring, ugly, “good enough” applications and, in general, enterprises tend not to attract great developers who love programming, and think and care about what they do. The quality of software in the enterprise world is not great.
Being the enterprise stack where the money is, software vendors try to sell something to them. They create huge, complex and expensive solutions not because they are good, but simply because they could sell them to enterprises.
Enterprises are often very risk averse and everything they do better be “standardized”. Standards are created either after some technology proved to be successful or before. In both cases, it’s bad for enterprises (and Java). Enterprises end up using either good technology too late or a downright failed technology. The latter case is also very dangerous because it creates a false perception that a technology (otherwise a complete failure) must be good if it is standardized and everyone is using it.
Historically, Java EE platform seemed to have attracted a lot of architecture astronauts and developers in big companies promoted to architects whose only purpose was to create more layers, more frameworks, more abstractions and more complexity.
It’s not that there are no good Java tools and frameworks; it’s that there are too many bad ones, too many over-engineered ones, too many bureaucratic processes and methodologies, too many useless standards.
In such a messy world it’s not just the particular selection of tools you choose that affects your productivity. It’s mainly about you, about your values, about how you can reject the majority of solutions proposed to you by the community, vendors, co-workers and managers. It’s about you going against the current, about your common sense, about you questioning every mainstream belief and “best practice”.
That said, tools alone are not going to change your productivity much, and conversely, the right people can be productive with inferior tools too.
My advice:
Don’t use a technology only because it’s standard, because everyone uses it, or because it’s officially recommended by Sun. Use a technology only if you personally think it’s the best tool for your job. This way you may find yourself rejecting technologies such as JSF, JSP, Web services, JMS, EJB, JTA, OSGi, MDA.
Keep it simple, use your common sense, question everything. Do you really need to publish your objects for remote access? Do you really need to create another abstraction layer so that you can switch from Hibernate to TopLink? Do you really need to convert your data to/from XML ten times every time you need them? Do you really need XML schema? Do you really need everything to be configurable are interchangeable? At runtime? By non-developers?
Keep the process simple. Be agile. Do you really need that documentation? Do you really need to describe every screen in a huge table, have it approved, type it in to some home-made tool and then generate JSP? Do you have competent programmers or you design everything first and programmers only “translate” to Java?
WYSIWYG design of HTML doesn’t work.
Graphical programming in general doesn’t work. This includes UML as blueprint and UML as programming language, MDA, drawing page flow diagrams. Code generation is bad.
Never design a framework prior to using it, always harvest a framework.
Prefer frameworks that have only little XML configuration.
Strive for low LOC count. Look at actual characters in your code. Is every character important? Think. What can you do to make your code smaller? Do you need that class? What does it do? Why do you need to do that?
Testing is not sacred cow; you don’t need 100 % test coverage. Test only what makes sense. If it’s difficult to test, make it simpler; or don’t test it at all. Don’t test visual appearance.
And finally, some concrete Java recommendations:
For presentation layer try Tapestry. Why do I love it? Because with Tapestry you can create beautiful code. It’s designed specifically for that, so that your code can be beautiful. Your code. By beautiful I mean everything that matters – it’s short, easy to change, easy to read, easy to create your abstractions, and still flexible, it doesn’t try to hide the fact that you are developing for the web. Of course, it’s still you who makes your code beautiful.
Feel free to use Hibernate, especially for CRUD and large apps. Don’t bother with JPA. It’s not a silver bullet though, with ORM you are always going to trade one set of problems with another.
Only a little Spring, you shouldn’t need much since you’ve carefully avoided all the Java EE traps. Use dependency injection sparingly.
After all of that, you may find the Java language too verbose and not very helpful when abstracting away you copy/pasted code. If you want to experiment, try Scala. The problem is that the main selling point of Scala is that you get all the benefits of modern languages while still keeping type safety, and at the same time, there is no solid IDE support. Being used to super-cool Java IDEs, it doesn’t make much sense to switch to Scala unless there’s an IDE support that is stable and reliable. Stable enough is not enough.
Frameworks like Spring, Hibernate, Wicket certainly help to simplify and accelerate web development as they provide a high degree of testability and integrate very well. But it's not enough to reach RoR productivity, even if you have a good set of development practices. There is still too much technical stuff and plumbing required.
Grails is maybe the missing piece in this picture to get closer to RoR. It's my next experimentation.
BTW, my MDA experiences are the contrary of a productivity improvement so I won't mention them (actually, MDA was killing our productivity).
Javarebel can greatly reduce time spent during web development using Java.
Let me quote here the official website:
JavaRebel is a JVM plugin (-javaagent) that enables you to see changes to your code immediately, without the need to redeploy an application or perform a container restart. If you're tired of watching the logs roll by, and want to see your changes so that you can keep going - JavaRebel is your new best friend.
One important point when discussing Java EE productivity: you should be using Java EE 5 and EJB3.x since they provide for new level of productivity (and functionality) compared to previous releases.
Staying within standard Java EE specs is absolutely important, e.g. using Hibernate instead of JPA is not beneficial to productivity. There is no limitation to fall back to Hibernate features when using JPA, but by using Hibernate instead of JPA you are locked in into single persistence provider with no cheap way out. The whole idea behind using standards is the same: conceptual flexibility (by plugging in different implementations) with available extensibility (by using proprietary extensions if absolutely necessary). Java EE 5 and EJB3 are huge steps in this direction. Of course, you want to minimize any proprietary features but if some seem absolutely necessary it's a good sign that they will be part of spec in next release...
Main obstacles to Java EE productivity are in its enterprise focus (offers a lot more than than needed for majority of projects) and in its legacy (backward compatibility). There is also a lot more to be done in presentation tier with JSF and state management - watch for JSR-299 to address these among other improvements.
Grails is a Java webapp framework very much modelled after Ruby on Rails, with similar principles (DRY, CoC) and productivity gains, but based on existing Java frameworks (Spring, Hibernate, several others).
I've been working on an exploratory project using Grails for a few weeks now (no previous experience in Grails or Groovy), and I'm quite impressed. There are a few rough edges - it's not as mature as RoR, but you can get results quickly and there's never the feeling that the framework is getting in your way.
Maybe it's best illustrated by this concrete example: I wanted to edit a 2D array of domain objects in a grid on a single webpage and found that the automatic mapping of the resulting HTML request data to the domain objects (provided by Spring MVC, I believe) had a bug that caused some data to be mapped to the wrong objects. I looked around on the web for an hour, but apparently nobody had encountered or solved the problem. Eventually I decided to forego the automatic mapping and do it "manually" - and then found that it took me no more than about 10 lines of code...
It's often cited that RoR and similar frameworks based on dynamic languages are more productive environments, but I am really interested to know if there are hard data to back this up. This wouldn't be easy, as one should be made certain that she is not comparing apples with oranges. Things like type of project (web 2.0, enterprise application) and team size should be taken into consideration. However, for small projects it is more than evident that such frameworks are indeed far more productive than Java EE. So this is a short list of arguments used to support this and what you can do for them in the Java world.
Ruby is a more intuitive and concise language. You can do the same thing with much less code.
I don't think you can have the same thing in Java, unless of course you use a dynamic language that runs in the JVM (JRuby, Scala, Groovy). Otherwise, your IDE can help. In Jave an IDE is an essential tool and it will pay you back if you learn to use it well (code generation, snippets, refactoring). In fact there are many things you can do with a Java IDE that are simply impossible to do with a Ruby or Python IDE. Plus you have the benefits of a static typed language. It may take more time to type, but it helps you avoid common mistakes.
Ruby is much more fun to use. Makes the developer happier and more productive.
Same as above. Highly subjective argument in my opinion though.
Convention over configuration makes things faster
A dependency injection framework like Spring or Guice can help
Scaffolding, MVC already there for you.
Again Java MVC frameworks can help
Databases made easy. Load database items as objects. Can change the database on the fly.
Hibernate, iBatis or another ORM framework can help. With Hibernate Tools you can achieve similar functionality with what you have in RoR with yml files
Load new modules instantly
Maven or Ant Ivy can help
Easy deployment for testing
Your IDE or Jetty can help. In fact debugging is easier with Java
Testing integrated with the framework. Use of mock objects facilitate testing
A dependency injection framework can help with mock objects. JUnit was a pioneer of unit frameworks. I don't think that Java is less easy to test.
I would definitely go for Spring together with Hibernate for persistency related stuff.
Why Spring?
The advantage of using Spring instead of another framework is that Springs philosophy is to be "non-invasive". Usually when you're using a framework most probably you'll start to depend on that framework which can be a bad issue if the application is considered to run for a longer time where you then have also to do maintenance etc. Spring uses the so-called "Inversion of Control" (IoC) pattern. Basically your code doesn't (it can but it doesn't have to) call Spring, but Spring will call you (Hollywood principle: "don't call me, I'll call you"). So for instance you can use normal POJOs (Plain Old Java Objects) and you don't have to inherit from any framework-related classes/interfaces.
Another big problem (if not the biggest) in Software Engineering are dependencies. You'll fight for reducing them as much as possible since they will make your life harder (especially in maintenance later on). Spring reduces dependencies among your components drammatically by managing the instantiation of components through configuration files and the dependency injection pattern. I wouldn't want to go on, the best thing is that you start reading some tutorials at the official Spring website. Initially it may need some time in the understanding but once you got it you'll earn a lot of benefits.
Since Jython 2.5 you can use django to satisfy the requirements you listed. It's pretty easy to generate war files from django projects and deploy them on J2EE application servers.
Just wanted to pitch in another idea... you can actually use JRuby and Rails (similar to the previous comment about Django and Jython).
If you use JRuby with Rails and JRuby Rack (and maybe some other utilities... I wasn't the one to actually get the integration going initially), you can deploy JRuby Rails additions to an existing Java web app. We have a legacy JSP application deployed with Tomcat, and are now starting to add new pages using Rails with just that setup (in addition to extending the JSP side when necessary). So far it has been quite successful, though we don't have any of the major high traffic pages implemented in Rails, so I don't know how well it will scale.
We have full access to the session, and have even set up mechanisms to invoke JSPs from Rails pages (such as existing header and footer type JSP includes). It takes some effort and trial and error to fully integrate the 2, but if Rails and JRuby is an option, I highly recommend it (as a personal fan of Ruby).
A colleague has dabbled in JBoss Seam, which is a framework by Gavin King (the guy who brought us Hibernate), which was meant to emulate Rails. Having seen both, I feel Rails is a lot easier to develop with.
Use AOP (Aspect Oriented Programming) for cross cutting aspects like logging, authorization etc. You can either use Spring AOP or AspectJ. It makes code clutter free and maintainable.
I've used Jboss Seam for the past couple of years and find it to be very productive way to develop in Java EE (utilising EJB3, Hibernate, Facelets). I also do the odd bit of PHP coding on the side and can honestly say that I'm more productive with Seam (although that's probably also an indication of my PHP skills.)
For me a couple of the highlights would be:
Hot deploy of code (an absolute must-have)
DRY with Facelets
Annotation based configuration
Extensive drop-in components (especially ajax4jsf)
IDE Support from Jboss Tools
There are tools in the IDE and from the command line to build skeleton code in a similar way to RoR.
Well, I'm not really a Java guy, so I can't say much, except for... JSF
We tried to use it for some time and it was a disaster. Almots all basics steps had to be passed with lots of pain, no documentation, no examples, no community knowledge. We used then one plugin for Eclipse (Exadel Studio), we had a look at a few other JSF frameworks, they were all incompatible and poorly documented. As a matter of fact, of all those we tried, only Sun framework (forgot its name, based on NetBeans) could create a new JSF project even compilable out of the box. The rest required many days of configuration of apache and other things, which for an unexperienced person is a real challenge (though I managed it).
Our team spent a few months on something which was done later in just a few weeks with ASP.NET. People were both inexperienced in JSF and ASP.NET.
If JSF ecosystem is still that bad as it was in 2007, I would recommend avoiding it altogether, productivity is out of the question anyway. Maybe stick with JSP or something that is time-proved and well developed?
I would go with the Lift framework written in Scala. You will see a great productivity boost just by switching to Scala. Scala is also very stable and it's extremely easy to call Java code from your Scala code. Not only that but it's quite similar to Java but with some added features. For some examples you should refer to 5 Things a Java developer needs to know about Scala. Twitter will move part of it's codebase to Scala.
You will never "get stuck" on a piece of code because you can just think about how you would do it in Java and write similar code. First class functions and actors will give you an even greater productivity boost and are both in Scala. Scala is of course statically typed and has a performance that is similar to Java.
I will quote the author of the Lift framework for an description of it:
Lift borrows from the best of existing
frameworks, providing
Seaside's highly granular sessions and security Rails fast flash-to-bang
Django's "more than just CRUD is included"
Wicket's designer-friendly templating style (see Lift View
First)
And because Lift applications are
written in Scala, an elegant new JVM
language, you can still use your
favorite Java libraries and deploy to
your favorite Servlet Container. Use
the code you've already written and
deploy to the container you've already
configured!
Some basic rules:
Kick out the appserver - a HUGE win in turnaround and quality. Keep a web container if you have to, but configure everything in Spring and/or Hibernate so the web.xml is minimal.
Test everything, which you can now do because of step 1 (no deploy-time XMLs or code generation needed: everything is configured in the development already).
Use Wicket to implement your web tier - nobody needs JSP any more; Wicket is 10 times more productive plus easy to test (see step 2).
Use SCRUM and agile development methodologies
The result is Java productivity as high as 4GLs allow - we at Atomikos have several migration projects we did like this. Because we migrated from 4GL platforms to Java/Java EE, we could compare the estimates in both.
Also see this blog post: http://blog.atomikos.com/?p=87
HTH
Guy
GWT seems like a really nice technology for Java developers who don't like (or don't know) HTML/JS/CSS to build rich web interfaces. On the server-side Grails also looks really nice, it's often described as "Rails for Java developers". I've read that Grails' "convention over configuration" approach, together with the benefits of dynamic languages (Groovy) can really reduce the amount of (boilerplate) code that needs to be written, while still leveraging best-of-breed Java technologies such as Spring and Hibernate.
Anyway, I haven't read much about how well these technologies play together. How easy is it to integrate GWT with Grails on the server-side? I'd be interested to learn about experiences of anyone that has build an application with these technologies? Recommendations on resources (books/websites) for building a GWT-Grails website would also be very welcome.
Cheers,
Don
Grails already has a gwt plugin: check it out.
You did mention on the server side - GWT and grails actually doesn't integrate well on the serverside (not as well as you might expect given how well grails domain objects work). For RPC, the plugin it works really well.
The problem is that domain objects cannot be serialized and tranfered across the wire - after all, they groovy objects. You will need to custom make a data transfer object (DTO), and do the marshalling manually. It is possible to automate it, but there isnt any opensource code out there that does it atm - so rolling your own is the only solution.
Or see if you can get Hibernate4gwt to work with grails - but i doubt it will out of the box either.
Another approach: use Grails with SmartGWT. Instead of GWT-RPC (too complex, and as others have noted, doesn't play well with Grails) use REST-based integration, since Grails has great support for serializing to XML or JSON and SmartGWT has built-in REST support. Take a look at this blog showing sample source - it's ridiculously easy to build a reusable master-detail screen for any Grails object.
http://josip-dev.blogspot.com/2010/06/grails-smart-gwt.html
with the benefits of dynamic languages
(Groovy) can really reduce the amount
of (boilerplate) code that needs to be
written
That's what folks from RoR camp was preaching all the time. After some initial boom RoR projects got into inevitable trouble with bigger projects. The bigger projects the more work one should delegate to compiler, i.e. the more valuable are static languages. Currently, RoR boom is all but gone.
The amount of (extra) code you need to write now with JPA/Hibernate, for instance, is almost zero. Annotations only. It even finds the mapped beans itself, in runtime, via classpath! SpringFramework makes many other "boilerplate" codepieces obsolete too.
In my GWT project (one so far, have to admit) I use JPA (Hibernate), DAO layer, business delegate pattern and it's easy and robust.