29 November 2010

Java EE and Spring: Why I couldn't care less

 Java EE or Spring - for an independent software architect, the question is just as relevant as Catholic or Protestant to an atheist. The question has recently been discussed in a number of articles mostly taking one side or the other:

In this post, I'll try to point out why I'm not fully happy with either of the two.

If there's one thing that matters to me, it's modularity. To put my cards on the table, I'm a strong OSGi supporter, but I'm not even religious about that - in fact, Living without OSGi (which is what I've been doing for nine months now) would be a nice headline for one of my next posts.

Seen from outside, Spring and Java EE share a number of shortcomings:

Preaching to the Converted

When did you last visit the official homepages of Java EE or Spring? Take a moment to click on the links and imagine you've never heard about either. After visiting the homepages, you are none the wiser, all you get is the usual marketing blurb and a couple of newsbites completely meaningless to the uninitiated.

Lack of focus

Java EE and Spring both are animals of the rare species Sus ovipara lactifera velluta unknown in English speaking countries which we call eierlegende Wollmilchsau in German. In plain English, they both try to be everything to everyone and end up doing nothing in particular.

In contrast, OSGi has a clear mission statement The Dynamic Module System for Java and provides a link to its key benefits right on its homepage.


Ever heard about lean development? Let's have a look at the official Javadocs:
  • Java EE 6: 1597 classes
  • Spring 3.0.5: 2312 classes


Backward compatibility is a good thing for veteran users of a framework. Users don't want to change all of their application code just for upgrading to a new framework version.

On the other hand, backward compatibility can be extremely confusing to new users: There's two or three solutions for the same kind of problem, the legacy one is not marked as legacy or deprecated clearly enough, tutorials and example code still use the old style, and you can only resort to your favourite search engine or to trial and error to make things work consistently.

Love Thy User

Don't just list what you can do for your users, ask them what they want you to do for them. Looking at the Java EE and Spring reference documentation, I can see that both frameworks solve lots of problems I've never had in my life.

On the other hand, looking for a solution for some specific standard kind of problem, it is often surprisingly hard to find a comprehensive code example.

User documentation should be structured by user stories, not by technology.

Enough Rope

Both Spring and Java EE give you enough rope to hang yourself. It's easy to write messy and ugly code on top of both frameworks, and I've seen enough of that.

You can write loosely coupled and elegant applications on top of either, but it takes a good architect to set up guidelines and restrict the number of choices.

Development Process Integration

As an application developer, you don't just write code to run on a given framework. You want to run integration tests on your applications, you want to deploy and debug them directly in your favourite IDE, and you want your batch build and continuous integration to be able to deploy your applications.

When choosing a framework, always consider the entire process chain - some lack of tooling for your favourite framework may be reason enough to pick the second best instead.


My ideal framework/container/app server - pick any name you like - would allow me to write truly modular applications, enforcing modularity at design time, at compile time, and at run time. The framework itself would be modular, allowing me to pick out those and only those modules actually required by my application.

It would actively support OSGi as the most mature module system for Java, and maybe a few others on top.

I expect some further degree of convergence between Java EE, Spring and OSGi within the next two years or so. There has been a lot slideware and a number of proof-of-concept or early adopter projects, but my feeling is that none of this has reached production quality yet.

To sum up, frameworks in general are alive and kicking, but the age of monolithic all-in-one frameworks is definitely over.

28 November 2010

Java EE 6 Integration Testing with Spring

Half a year ago, I created and published the jeeunit project to fill in some gaps for running integration tests on Java EE 6 components in an embedded EJB container, mainly targeted at Embedded Glassfish 3.x. One of the alternatives I considered and dismissed before writing my own solution was the Spring Test Context.

At the time, I was left with the impression you had to pollute your Java EE components with Spring annotations like @Transactional to make declarative transactions work in the Spring container, and I did not (and still do not) like the idea of writing XML just to create a couple of Java beans and wire them up.

After taking a closer look at Spring 3.0.x these days, I realized a number of facts which are not quite obvious from the Spring reference manual:
  • You can do most of your Spring configuration (but sadly not all of it!) in Java instead of XML, which makes your application context type-safe and easier to read, and gives you refactoring support from your IDE.
  • Spring supports some (but not all) of the Java EE 6 annotations as alternatives to its own flavours.
  • You can run Stateless Session Beans and JPA entities in a Spring container with declarative transactions without introducing dependencies on Spring APIs or annotations.
jeeunit now includes an example project jeeunit-example-test-spring demonstrating this approach. The details are documented in the jeeunit Wiki page Testing on Spring.

This solution is not intended to replace the original in-container-testing approach of jeeunit, because transactional Spring beans and EJBs have different run-time semantics. However, for many integration tests, these differences are irrelevant.

Using the Spring Test Context instead of Embedded Glassfish and jeeunit has two main advantages:
  • Spring starts noticeably faster than Embedded Glassfish.
  • Launching a single test from your suite is much easier than with jeeunit. E.g. in Eclipse, you can simply use Run as JUnit Test just as with plain old unit tests.

04 November 2010

CDI - A Major Risk Factor in Java EE 6

Update 18 Dec 2010: This post mainly relates to Glassfish 3.0.1. As of 3.1-b33, the situation has improved a lot.

Evaluating platforms and architectures for a new enterprise web application earlier this year, around March/April, scheduled to be released in 2011, I was bold enough to settle on Java EE 6.

In retrospective, I do not regret this decision, but I had to spend a significant amount of time analyzing and debugging platform problems. Based on this experience with Java EE 6, which may not be representative of course, the only advice I can give is: When Java EE 7 is released, wait a year or two before using it for production, unless you have the time and resources to act as beta tester.

The Java EE 6 specifications were released in December 2009, together with Glassfish v3, the first "production-quality release" of a Java EE 6 server. "Marketing release" would have been more appropriate, since going by the number of bugs in Glassfish 3.0, the main driving factor for the release date was quite obviously not a quality benchmark, but simply the need for Sun as the Java EE champion to release a working server simultaneously with the specifications.

The Problem

Java EE 6 was advertised as the lightest Java Enterprise Edition ever, with Contexts and Dependency Injection (CDI, JSR-299) as one of the most prominent innovations. However, for my project, CDI in the guise of Weld, its reference implementation, turned out to be the largest single source of problems. In addition to a number of functional bugs where injection would not work in certain scenarios, there are at least two severe memory issues:
  1. Weld causes memory leaks on application redeployment.
  2. Even in the first deployment of an application, Weld uses enormous amounts of memory.
The first issue had plagued us for months, and my team had grown accustomed to kill all Glassfish and Eclipse processes after three or four redeployments and to re-initialize their entire workspace, which was rather a pain.
Investigating the memory leaks using the Eclipse Memory Analyzer, I realized that Weld claimed almost 90 % of the heap memory of my application. Most of this was due to instances of org.jboss.weld.introspector.weld.jlr.WeldClassImpl, which appears to be a reflective model of a class inspected by the CDI BeanManager. Some instances of this class were as large as 1 MB.

I should add that our application uses Wicket for the web front end, injecting EJBs into custom Wicket components. Custom components inherit from Wicket base classes with a fairly deep inheritance hierarchy and a large number of methods. This accounts for the size of the reflective models.

Our usage of CDI was fairly basic, so it was just an hour's work to replace all @Inject annotations by Java EE 5 style @EJB annotations. After that, the heap usage of our application was reduced by 90 %, we no longer had any memory leaks, and we finally had a hassle-free edit-save-debug cycle in our development environment.

The figure of 90 % heap usage by Weld was observed on Glassfish 3.0.1, running on a 32-bit JVM on Windows XP.

This week, I retested the same application with Glassfish 3.1-b26 (using a newer version of Weld), running on a 64-bit JVM on Ubuntu 10.04. The result was not as drastic as before, but still about 50 % of my heap memory was consumed by Weld.


This article is mainly about problems with the CDI reference implementation Weld, not about CDI as such. But these implementation details have a ripple effect:
  • Glassfish 3.x still is the only certified Open Source Java EE 6 server. It uses a newer version of Weld in the current 3.1 promoted builds, but I can see no indication of the Weld issues being solved in time for the 3.1 release.
  • JBoss AS 6 is likely to be the next in line for full Java EE 6 compliance. However, JBoss also includes Weld, so you're bound to run into the same kind of problems on JBoss.
  • There are alternative CDI implementations, CanDI from Caucho and OpenWebBeans from Apache. Unfortunately, unlike JPA, there is no pluggable CDI provider interface that would allow you to simply replace Weld by some other CDI implementation on Glassfish or any other server.
  • I tried running my application on Resin 4.0.8 to see if CanDI was any better than Weld. However, Resin had bugs in the JPA and EJB areas and I was unable to deploy my application, let alone run and monitor it. (Resin only aims at supporting the Java EE 6 Web Profile, but that would have been sufficient for my case.)


All in all, if you want to work with Java EE 6, there is currently no way around Weld. And until Weld reaches production quality, the only way to build production quality applications on Java EE 6 is to avoid using CDI.

Free and Open Source Software is all about choice - so I would really love to see a pluggable CDI provider interface that would allow users to work with Glassfish and some CDI implementation other than Weld.

The second best solution might be to join forces from different CDI project to make Weld stable enough for production usage.

The third option would be another fully Java EE 6 compliant Open Source server (maybe Geronimo?) not including Weld.

No idea if any of these options is realistic, but this is on my wishlist for 2011.