onsdag, maj 17, 2006

JavaOne, day 1: some diverse impressions.

So, JavaOne is finally here, and it starts big! This blog will talk some about the different sessions I've been to during the day, but first a few impressions. There are very many people here. John Gage said at the first general session that this is the largest JavaOne ever, and I believe him. I'm sad to say that the WiFi network is very spotty at best.

JavaOne has a new way of getting into sessions; you have to use their schedule builder to reserve places for a session, and then use your RFID chip to register when entering a specific session. I thought this was a mad idea, but it actually works really well, and I'm glad to say that the JavaOne team seems to have solved most of the overflow troubles from last year.

Another small reflection is that the focus on compatibility in the core platform seem to be a major focus this year. I've seen and heard the word spoken more times than I can speak.

General session
The first general session is always one of the more interesting times during JavaOne. Both Sun and other company leaders are just brimming with announcements. One of the more interesting quotes of the day came fairly early, from Rich Green: "It's not a question of whether, it's a question of how". As you may guess, this was an answer to the question of open sourcing Java. In plain language the situation is that Java will be open source, as soon as Sun finds a good way to do it in.

Java Enterprise Edition 5 is now finished, released and of production quality, and these are some highlights from the release:
It's very focused on ease of development.
Contains much Web 2.0 support.
Interoperability with .NET have been greatly enhanced. (Except for compatilibity, interoperatibility is the major illy today).
SOA has been simplified.
They have simplified the programming model, mostly by using annotations.
New EJB version, using plain old Java objects.
A new (annotation-based) persistence API.

During the general session, many, many libraries and applications were open sourced, among these JMS. It's nice to see that Sun really wants open source to work.

Session on EJB 3.0
The idea for EJB 3 was to make it easier for the developer, by making the container harder to implement. This tradeoff seems reasonable in retrospect, but until now most of the EJB specification made it easy for the container.

The new model is based on letting the container provde requested services to the bean, and also using reasonable defaults for most operations.

Once again, the presentation pressed very hard on compatibility. Existing applications had to continue working. Clients using the new API should have no trouble connecting to servers using the old libraries and the other way around.

Most of EJB 3.0 is based on POJOs and declarations with either annotations or XML information.

Environment access is made easier with dependency injection or simple lookup.
Client code also uses dependency injection, which means the new model removes the need for home interfaces, PortableRemoteObject.narrow, RemoteException and other checked exceptions.

The EJB lifecycle doesn't use explicit callbacks anymore. Instead you can annotate the method that should get notifications about a lifecycle change and this will be taken care of by the container. You can also allow a separate interceptor as the notification and callback manager. Very neat.

All in all, EJB seems to be heading the right way, at last. Ease of development really matters, and configuration by reasonable defaults have already been shown to be a viable solution.

Technical general session
The technical session had some interesting information too. Most of the talk was about Mustang (Java SE 6) and Dolphin (Java SE 7), and what we could expect from these releases.

The projections for Mustang looks good, and it is scheduled for release in October. They have been using a new, very open process for Mustang development, which have worked extremely well. The same system will most likely be used even more in Dolphin development.

So, some nuggets of good stuff in Mustang:
Many performance improvements. They showed some pretty convincing performance graphs, and I was duly impressed.
They've fixed the so called gray rect problem in Swing, which results in heightened perceived performance dramatically.
There is many improvements in the monitoring and management areas.
Scripting support will come, with JSR 223. Also, check out http://scripting.dev.java.net.
There are many desktop fixes, and Vista is the desktop focus for Mustang.

The talk went on to the future for Standard Edition:
Probably direct support for XML in the language.
Super packages, and new module system for packaging with versioning.
They're thinking about adding BeanShell to the scripting languages provided by the core language.
And more, more,more desktop stuff.

Hamilton went on to talk about scripting- and dynamic languages, and more or less recommended using them in the Web tier and in situations where a fast cycle of development is required. This layer can then use Java for the business logic. (And this is really what KI is heading for right now; using Ruby on Rails for web, and using SOAP to get at Java business logic exposed with Web Services.)

Anothing thing that's coming is JSR 292: the new bytecode for dynamic invocation.

An interesting demo of a Visual Basic to Java compiler. The system is not a total clone, but will enable people used to Visual Basic to program for the JVM instead. It will not enable translation of existing applications, though.

Mustang and Dolphin session
This session started out with Mark commanding us to upgrade to Tiger now, there is really no reason not to do it.

So, what's new in Mustang?
Some class file changes.
A new Compiler API.
New annotation processors.
Scripting support.
Streaming API for XML.
Common Annotations.
and JAX-WS 2.0.

Mark top ten list of new things in Mustang:
10. Attach-on-demand monitoring.
9. Plugin API for JConsole.
8. jhat OQL (a query language to explore heap dumps).
7. Solaris d-trace.
6. javac will now do annotation processing interleaved with compilation.
5. Classpath wildcards!
4. API for finding free Disk-space.
3. API for password prompting.
2. New Grouplayout for Swing.
1. That JAX-WS can do RESTful web services.

Mustang will also bundle Apache Derby, a small inmemory database.

There are many ideas for what Dolphin will contain. There are some interesting things that can be really cool.
These are mostly core language changes:
Properties, improving getters and setters.
Real method references.
Block closures.
Native XML support.
The new bytecode for dynamic invocation.
Bundling BeanShell.
And beans binding for making Swing more easy to use.

The session also had some very fun information about how the testing of JDK is done. It's really quite amazing. The big trouble with creating new versions is disconcerting fact that running a full test cycle takes 10 weeks.

Session on the new Concurrency features in Java 5
The session began with some talk about the rationale behind the new concurrency features in Java. The easy answer is that real concurrency is hard to do right, and the builtin primitives for threads and locks are, well, primitive.

The new concurrency packages have something for everyone. There is both easy-to-use utilities for mostly anyone, and also some primitives for hard core programmers, that enable some things that just can't be done in Java right now.

Java has always had thread-safe collections, but these are not conccurent. They also had a bad performance structure. Therefore a few new conccurent collections has been added. Most of them allow unlimited reads and up to 16 simultanous writes. Mostly, the semantics are the same, but they differ in a few areas. The most glaring difference is iterators. With the old collections you got a ConcurrentModificationException if someone updated the collection while you were iterating over it. This will not happen anymore. Tiger has a new Map called ConccurentHashMap and Mustang adds a SkipListMap.

A new collection interface has been added to java.util, which is called Queue. This is a subset of the List functionality, that can be used for implementing high performance versions with just this restricted functionality.
The most interesting Queue is the BlockingQueue, which makes explicit a producer-consumer relationship. Mostly all code already uses something like it, but this implementation is industry strength and very easy to use.

They have hadded ThreadPools with a system of Executors and ExecutorServices. They are very easy to use and configure with factory methods.

Another interesting addition is Future and Callable, which is used to put an execution inside another thread and then get the value when it's finished. But it is not
call-by-need, which was what I first thought. The value will always be calculated, even if it's not needed.

Scheduling primitives have been added, to replace Timer and TimerTask.

There are also some new advanced features for locking. There are some things you just can't do with the synchronized keyword in Java. Hand-over-hand locking is one example. The concurrency library adds Locks, Conditions and Semaphores for more advanced use. They are very complicated so they shouldn't be used if you don't really need them. One good reason for this is that you have to release locks manually.

JUnit next generation
JUnit has many warts and problems. How do you run one test in a test case, for example?
It's not really good for anything but unit testing. It has been very few updates and the
protocol is intrusive. It also uses a very static programming model. And it doesn't use the latest Java features.

TestNG is the new JUnit. It uses annotations for most configuration. There are test groups which can be dynamic depending on your needs.
You also have the possibility to have dependent tests, parallell testing, load testing and partial failures. It has also got a very nice plugin API.

All in all, it looks really good. My personal opinion is that there is no reason not to use TestNG instead of JUnit on all
Java 5 projects.

Restructuring a web application with Hibernate and Spring
This was the first BOF for me this JavaOne and I was very disappointed. The presenters use case was a web application that had been badly written from the beginning. They then decided to rewrite it with Hibernate and Spring, but there really didn't seem to be much better code written for this application. I guess it's a testament to how good Spring and Hibernate are, that they got a really good performance improvement anyway.

Testing a persistence layer
Testing a persistence layer is really hard, for a few different reasons. You want it to be fast, and easy to write. There are many different strategies to testing persistence, and the presentation talked about most of them.

There are a few different kinds of persistence layers. They can be SQL-based, Object/Relational-based or using the ActiveRecord pattern (which the presenter viewed as a special case of SQL-based persistence).

As noted above, there are many strategies available.
You can mock the DAO's for testing the business logic. This is easy if you use a dependency injection framework like Spring to initialize the DAO objects. Otherwise this is the main problem. It's very fast but the scaffolding can get hairy to write.

You can also mock the ORM-framework, to test the DAO's. The presenter have written a utility called ORMUnit to faciliate this testing.
Regarding mock frameworks, the presenter prefers JMock, but is planning on migrating to EasyMock instead.

Another strategy is to test the metadata mapping and schema. This checks for stupid errors like forgetting to map a field. It can also checks that all referenced tables and columns actually exist.

Of course, the standard way of testing persistence, by doing CRUD operations is also available, but it's complex, and very slow. You have to write much code to drop and add data for each test.

Another simple way is to check the generated queries directly, to see that they return correct data.

Using an inprocess database can be very fast, but may also lead to trouble with incomplete SQL implementations.

A final strategy for testing slightly things faster is doing operations but never committing transactions. This has the advantage of being fast and also avoids actually changing the DB.

All in all, it was a busy first day. Much of it was very interesting, and I've learned many new things. I just regret missing the Scripting Languages BOF at the end of the night, but I was just to beat to manage going to it.

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