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Good Java application server for ORM [closed]

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Closed 10 years ago.
I just had a chat with a far more experienced and qualified colleague about JPA and application servers.
Right now, I am using JPA with Glassfish, which he says is a bad application server due to the amount of overhead. He also mentioned that he's using Tomcat, which is a standard, which also has a downside of not supporting heavy-weights like JPA in the Java EE. Then a few names are thrown around, like Hibernate and Spring, which I've heard of but not dealt with.
So my question here would be: What are some good choices for an application server that supports Java EE and JPA that's also popular and fast?
Note: I asked a similar question in the past and it was, somehow, closed as non-constructive. If you find this to be a non-constructive post, please write a response detailing why before closing this.

What are some good choices for an application server that supports
Java EE and JPA that's also popular and fast?
What server you choose depends on your needs. If you don't need in your application any of the EE features (EJB, transactions etc) then using a heavy-weight server doesn't make much sense and you could opt for Tomcat which is compliant (partially to the specs) lighter (doesn't have all these dependencies that you would not be using anyway) and gets the job done.
If you want specific reviews about all application servers then may be you should do some research and see ask which server suits you better for your requirements. But this is just my opinion...

I'm using Jetty with JPA Hibernate implementation, and it works really well. Out of the box, it is only a subset of JavaEE specs, but it is lightweight and can be extended with external libraries to add missing JavaEE parts.
(My standalone jetty-based application runs with 160MB available RAM on an embedded system)

As per me : The JBoss is the most popular and stable open source application server.
A good discussion available at Stack Trace

I would recommend you to first understand your application needs, and understand why you need JPA.
I have nothing against JPA, but in some scenarios it may introduce a performance issue, that you don't want you application to have.
Having said that, I would recommend you to work with a server that supports EJB-Lite.
You can use for example JBoss as suggested above.
Another interesting option is to use TomEE , which provides a full stack of web-profile over tomcat.

You can use JPA outside of a full Java EE server, but it has to be properly bootstrapped. I believe Spring has ways to do this, and would allow you to use JPA in tomcat, jetty, etc...

You have many options to choose Java EE application servers. Here is the comparison of popular Java EE servers from Wiki. They all are good application servers. But the most important thing is not server.Using a server that is more convenient for your developing environment is more important. Choose a server that is more convenient for you.

Which workflow engine to choose? [closed]

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Closed 10 years ago.
We are currently in the process of evaluating a BPM engine and I'd really appreciate the community input. I am doing my own due diligence but would also like to hear on the suggestion based on implementation stories.
My main evaluation criteria are below
open source and OEM friendly license
production installations (success stories are a great help)
commercial support available
open standards support - BPMN
dynamic creation/assembly of the workflow based on input
embeddable
Currently I am evaluating Activiti and JBPM. Bonita open BPM seems like a good candidate as well but never used it. Do you guys have any successful deployments on Bonita?

I've just been doing an evaluation of Activiti vs jBPM.
In fact there seems to be very little between the two solutions.
Activiti is Apache V2, jBPM 5.0 is also Apache V2.
We're currently using Activiti, but the project is still in dev, so I can't comment on its robustness in production.
jBPM is beginning the productization process, so support for 5.x will be available in Q1 2012, see slide 32: jBPM demo. jBPM 4 was not supported by Redhat.
jBPM 4.x did not support BPMN 2.0, but 5.x does, Activiti does as well. jBPM 5.0 has just been released, which includes support for BPMN 2.0. So now both solutions support BPMN 2.0.
I'm not quite sure what you mean by this, but you can do a lot through both APIs
Again, not sure what you mean by this, do you mean embedded as part of an application server, in which case, yes for both solutions.
One of our criteria for jBPM was the interaction with Guvnor, and when I downloaded and ran the demo install for jBPM (28/03/2011) and there still seemed to be some major bugs (GUVNOR-1274), so I personally would test a lot more before I chose to pursue this solution.
In fact, we will be recommending one of the above two solutions, but we're not sure which yet, we'll look at it more closely later this year.

Although I have little practical experience I did undertake a research spike into java BPM options recently. I narrowed it down to 3:
jBPM
Drools
Roll your own
The Drools community seems more active, tools are better, the rules engine was very sophisticated (as this was the base of drools) but surrounding business process were well integrated. However jBPM was more focused around business processes and slick as well. They are both managed by JBoss
Further comparisons between Drools and JBPM can be found here:
Drools v jBPM
If you have a confident development team and the requirements aren't too complex it is always worth considering rolling your own. BPMs can lead to anaemic domain models (as described in this post Rules Engine pros and cons about rules engines ) as you try adopt your domain models to fit into such systems, also well built systems customised for your business are always going to be more effective.
As far as your criteria goes:
Open-Source and OEM friendly license - Drools uses a liberal 'ASL/BSD/MIT-esque license', community is active. jBPM uses apache, eclipse and MIT licenses
Production Installations. I understand drools is used by many insurance companies and credit checkers, not sure a jBPM
Commercial Support available for both
Open Standards Support - BPMN - Both implement BPMN and due to the nature of the open source projects are very standards orientated.
Dynamic Creation/Assembly of the Workflow based on input. Both, although is generally easily implemented manually.
Eembeddable - both offer entire systems but are modulated so this should suite embedding into existing systems.

My not use an MS stack? WWF 4.0 for the engine, re-hostable designer. WCF for communication. MS Sql Server for BI. Plenty of .NET devs out there to help build and customise. Other than a Windows target, no dependency on an external supplier.

Java EE 6 vs. Spring 3 stack [closed]

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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

What to learn for making Java web applications in Java EE 6? [closed]

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Closed 10 years ago.
My goal is to make web applications!
I finished reading the Books "Headfirst - Java" and "Headfirst - Servlets and JSP".
Because this topic (web applications) is so big and complicated, I would like to ask what I should learn next. I feel overstrained when I read catchwords like Java EE, EJB, JSF, JPA, Glassfish ... but I won't give up.
Can anyone please tell me how I should proceed with learning? Should I grab a book like this:
Beginning Java EE 6 Platform with GlassFish 3: From Novice to Professional or should I just make some Online tutorials?
Thanks!

Even if I know that this will be controversial, my advice would be to start with Java EE 6 only. So, grab GlassFish v3 and either get the book Beginning Java EE 6 Platform with GlassFish 3: From Novice to Professional or follow the Java EE 6 tutorial. In my opinion, the book (that I've started to read so I know what I'm talking about) provides more guidance which might be preferable if "everything" is new for you (it covers both the Java EE platform and its APIs and the environment to build, deploy your applications).
Now, as I said, I can already hear voices saying things like "Java EE is heavy, use Spring instead, learn Struts or Wicket or Stripes for the presentation layer, learn Hibernate for persistence, or not because I don't like ORM, use iBatis or straight JDBC instead (you'll see, it's cool with Spring, Spring is so cooool), and use Tomcat (and why not Jetty), or JBoss, or just forget all this and go for Grails, and bla bla bla...".
But I don't think that this is really helping you and, without mentoring or guidance (and you won't find a non outdated unique resource covering all combinations), this must sound very confusing for a beginner.
So, because I think that Java EE 6 is a big improvement over previous versions of Java EE, because it provides really nice standard APIs for all your needs (Servlet 3.0, JSF 2.0, JPA 2.0, EJB 3.1 lite, Bean Validation 1.0, CDI, etc), because these APIs are all more than decent, because there is nothing really wrong in learning them, because this is already a big task, because you have to start somewhere, I'd focus on Java EE 6 only and forget the other frameworks for now. More precisely, I'd start with the Java EE 6 Web Profile (and then add things if you want to go further).
By doing this, 1) you'll get started and you'll learn brand new things and 2) you'll give some time to all other frameworks and/or tools to adapt and prove that there is still a need for them. And if there is, it will still be time to experiment the survivors and you'll be able to understand much better why they exist.

My advice1 is to stop reading books and start implementing stuff. In my experience, book learning is poor a substitute for the knowledge you get by actually doing things.
Obviously ... you can come back and do some more reading later. And you will probably get more from the reading when you do.
1 - Context: this is advice to someone who has just finished reading two books on the topic, and is looking for more books to read. In practice you need to balance reading with doing.

Java EE 6 is really amazing. The only problem is that it's about 2 weeks old, and there is only 1 container currently offering it's features -- Glassfish.
I have nothing against Glassfish, I use it all over the place, several production instances, I love the product and the project.
That said, the details of Java EE 6 do not translate back to Java EE 5. Some do, many do, but the Web Profile, Servlet 3.0, the new Bean types, JPA 2, etc. Those aren't there.
So, by learning Java EE 6 first, you're simply constraining yourself to a single container. More are coming, but they're not here yet.
Tomcat, JBoss, OpenEJB, Glassfish, Jetty, Resin, Geronimo, etc. all work well with the Java EE 5 spec (at least those parts of the spec that they support, Tomcat doesn't have EJB for example).
I can't think of anything in Java EE 5 that wasn't carried forward to Java EE 6. Java EE 6 made some very old aspects optional, and those you simply wouldn't learn today anyway. Java EE 6 made some Java EE 5 stuff even easier (packaging notably, EJB Lite for example).
Learn Java EE 5 now so that you can actually apply what you learn in a variety of environments, rather that learning Java EE 6 now and discovering you may not be able to use much of what you learn.
No single book will teach you what you need to know. Servlets, for example, are a nice foundation, but for anything larger than a couple of pages or endpoint, you will want to use one of the many 3rd party frameworks, or JSF, and no book covers the core and then a framework on top of that.
The Java EE 5 tutorial is good at getting the foundations down, my major complaint is that they don't show you the source code. Rather they expect you to just download and run it. It's not discussed in the tutorial. I've found the Head First books to be pretty good.
For web programming, raw Servlets are important enough just to understand the request/response cycle but you don't need a deep understanding to make a leap to a 3rd party framework.
I'm a big fan of Stripes for an Action framework (vs a component framework), and the single Stripes book available is excellent (making choosing that an easy choice).
I can't suggest a Component framework book, and I actually would not recommend one right off. The component frameworks truly bury the HTTP core request/response structures. They bury them for a reason, and they gain value BY burying them, but I believe to be effective you need to have a solid understanding of these concepts early on. That's why I don't suggest learning a Component framework first.
The JAX-RS REST framework, included in Java EE 6, but readily installable in Java EE 5 or any servlet container, is excellent. Arguably it is what Servlet 3.0 should have been. But I don't know any books for that.

For Tomcat, read the manual on the website. It is very good. Particularly, the first few chapters on web app organization and deployment, and the chapters on the Servlets API and JSPs.
For Spring, the Manning book Spring in Action is very good. Similarly for Hibernate (the Manning book) but I think Hibernate is mostly outside the scope of webapps. Your call, though.
Wicket - Manning book also. But really, just write your front-end code in Javascript. It will be less painful, IMO.

I won't comment on other technologies but if you want to learn Hibernate get "Hibernate Made Easy" by Cameron McKenzie(www.hiberbook.com). It is worth every penny. You can finish reading that book in 2 days(literally). it is like a novel and at the end you find yourself dealing with Hibernate like a Semi-Pro.

Jpassion provides good videos and material to learn Java EE 6 and other stuff.
You should also see applications examples:
Petstore. Requires Maven, Glassfish recommended. Written by Antonio Goncalves who wrote the mentioned book.
JBoss Ticketmonster. Requires Maven & Jboss Forge. Deploy in Jboss.

If you just want to create web applications in Java, check out the Play Framework. It is similar to "Ruby on Rails"

Running Apache Geronimo in production

If you're running Apache Geronimo in production why did you choose it over other application servers and what are your experiences with running Geronimo in production?
Can you also please share what servlet engine you decided to use (Tomcat/Jetty) and why you made this decision?
UPDATE: So far this question got two up-votes and one star but no answer. I'm starting to wonder, is anyone using Apache Geronimo at all? My logic would be, if you use Geronimo for development you'd also use it for deployment. Right? So, does that mean that no one is using Geronimo at all?

We definitely use Geronimo in production!
We have used the Tomcat version since 1.0, about four years ago as I recall. We are currently running mostly 2.1.1.4.
One of our apps gets about 1 million page views per day. The others are nowhere near that, but they are important apps that need to work well.
Our choice was based primarily on:
Price: At the time our company started using Java, we weren't sure what we needed out of an app server. So we decided to start at free and work our way up, if needed.
Basic features: I had experience with WebSphere (base/ND) and plain old Tomcat. Geronimo had the J2EE features we wanted, all within a lightweight package.
Open Source: Our primary client that we use Java for required Open Source.
Familiarity: Being an Apache-based server, we were already comfortable with Tomcat, OpenJPA, Axis web services, and others. Furthermore, we were comfortable with the Apache community as far as bug tracking and other minor things.
Support: We expected to be mostly on our own, but knowing that the Apache community was active was important. As was the availability of commercial support from IBM, as we are an IBM Business Partner.
Our experience has been great overall. The servers are very reliable. I search our logs once in awhile and sometimes see weird errors with a database connection, an EJB call, but those are pretty rare (and quite possibly our code's fault).
Performance is impressive. I joke that we could run Geronimo from my laptop and the clients wouldn't see a difference. Give it any decent server and it will purr along for months.
I'm not sure how many people actual run Geronimo. I'm rather confused about that. I've seen slides (years ago) that listed some big names like eBay using it. The mailing list is active but sometimes seems like only the Geronimo team communicating with each other.
The only serious bug I've run into is this one. It is a big deal to us, but of course Geronimo is free and I don't expect them to fix bugs that are important just to me.
I've been meaning to check out Apache TomEE server, wondering if it is more actively or openly used. Just to see how the community and usage compares to Geronimo.

WebSphere community edition is Geronimo. So IBM chose it as a platform of choice.
When choosing an application server, you're really choosing the APIs you want to use in your application and maybe the administration interface (but you only use that once in a while).

Answer to your update: It just means that SO users are not using Geronimo or are all busy voting and making witty comments.
There seems to be quite a bit of acivity on Geronimo's mailing list, and I would say that you'll get better results there.