Category Archives: Java/Java EE

Live from JavaOne: EJB 3.1 New Features

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I’m blogging live from the floor of the Sun JavaOne Conference in San Francisco today, currently attending a session about the new features of EJB 3.1. This article highlights some of the much-needed features added to the EJB 3.1 specification.

1. EJB Singletons (finally!)
The EJB 3.1 specification will support shared session bean instances without using a Java static object. Singleton session beans are added with the @Singleton annotation and are created per application, per JVM. The new features of a singleton object require a number of concurrency enhancements, referred to as bean-managed concurrency and container managed concurrency, which essentially supports read/write locks for the singleton object, helping to ensure proper access from multiple concurrent clients.

2. Dynamic/Portable JNDI names
When EJB modules are deployed, JNDI names are auto-created for each bean as follows:

  • Global: java:global/[<app-name>]/<module-name>/<ejb-name>
  • Same App: java:app/[<module-name>]/<ejb-name>
  • Module: java:module/<ejb-name>

3. EJB Timers
Added cron-like support for EJB timers. Seems identical to Java Quartz, but I’d have to see the lower level details to see if they are related. Timers can be created via annotations or explicitly in Java code and seem to have a much larger expressive language for creating schedules.

4. EJB Lite
Subset of the EJB implementation allowing vendors to create and support EJB environments with a much smaller overhead. Not sure how helpful this will be in practice since most vendors are currently used to creating full EJB implementations and creating a new, smaller subset will require some amount of non-trivial work.

5. Asynchronous Session Bean Invocations
Add asynchronous support for remote/local enterprise bean. “Fire and forget” with results available from Java concurrent Future API. Example:

@Stateless
public class HelloBean {
...
@Asynchronous public Future<int> getHelloValue() {...}
}

More to come
There were other things discussed in EJB 3.1 specification such as interface-less local beans, testing EJBs, startup/shutdown callbacks, and JAX-RS integration, but I’ve covered the ones I find most exciting. Overall, the Singleton aspect has to be one of the most needed features of EJB. More to come from the JavaOne conference this week!

See you in San Francisco!

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I’ll be away this week from June 1-5 attending the Sun JavaOne Conference in beautiful San Francisco. I plan to expand my knowledge of advanced J2EE/SOA topics as well as pick up some introductory courses on new technologies. If you want to meet up to discuss any of my recent articles, the conference, or how cold San Francisco seems to be this time of year, drop me an e-mail!

San Francisco

Why JDBC + JSP = Bad

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Over years of moderating at The JavaRanch, I’ve seen one type of question spring up on a weekly basis: that asked by people who need help with JDBC code inside of Java Server Pages (JSPs). As much as we may want to help this individual fix their particular problem, the overriding thought of “STOP WHAT YOU’RE DOING” often prevents us from doing so. The purpose of this post is to explain why putting JDBC code inside a JSP file is akin to shooting yourself in the foot. With a shotgun. While not wearing shoes.

Don't use JDBC inside of JSP pages

1. You cannot reuse the code
First and foremost is the issue of code reusability. While importing java classes is quite common, importing code from a JSP is not. While you can write JSP functions, although I never recommend doing so for reasons I won’t get into now, you’re basically writing code that you cannot be used anywhere else, particularly in non-JSP java classes. The most common counter response to this is “Well, I don’t need to use it anywhere else”. Yes, you do. Whether its just reusing code for making the connection to database or the code for performing a query and reading the results, it will be used again at some point in the future in a way you have not thought of yet. Unless you are being paid by the line and prefer this sort of thing, it’s a bad move, and I guarantee your code base will be much larger than someone who put all their JDBC code into normal Java classes. Larger code base means more difficulty to maintain and more headaches for you down the road.

2. You are mixing business logic with the presentation layer
Probably the most overlooked issue for inexperienced developers is the fact that you’re mixing the business/data layers with the presentation layer. I’ll put it another way, if your boss comes in one morning and says we’re throwing out the JSP front end and replacing it with a web service, Java Swing, Flash, or some other interface, there is virtually no way for you to reuse the database code without going through every line of every JSP file by hand. If the database code had been placed in plain java files, then you would have a path for packaging the JDBC code into a single JAR and making it available as a service to a different front-end client such as a web service, Flash, etc.

In enterprise development, the presentation JSP layer and the database are often separated by multiple layers of indirection such as described by the commonly used three-tier architecture pattern. Those who are just starting out programming often do not know why mixing these layers is bad, but I promise you if you stay with software development you’ll understand one day.

3. But it’s just this once!
Often times, JDBC code enters JSPs by developer lying to themselves saying “Well, it’s just this once” or “I just need to test something”. Instead of being removed when the developer is done ‘testing’, the code often persists for a long time afterward. Furthermore, putting your JDBC code inside of reusable Java classes makes testing go faster! Spending 10 minutes setting up a single reusable Java JDBC class will save you hours down the road. Then, if you want to test more than one JSP page with JDBC logic, you already have your Java class file to start with. Proponents of test-driven development tend to understand this better than anyone.

4. It’s really hard to maintain
Code maintenance is another topic that new developers do not fully appreciate since they have not spent years maintaining the same code base. Unless you write the most beautiful JDBC code imaginable, its very difficult to read through huge JSP files looking for bugs and/or making enhancements. It’s a lot easier if all the JDBC access is restricted to a set of files much smaller in size than the JSP code base.

5. It’s a really bad practice
If after reading this article you still do not fully understand why you should not put JDBC code inside of JSPs, let me simplify the issue by saying “Just Don’t Do It”. Whether or not developers understand the reasons against doing so is not as important as stopping them from doing so in the first place. In short, you create code someone else (possibly yourself) will have the misfortune of maintaining down the road.