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Wednesday, March 29, 2006

Cognition: Tapestry 4 + Hibernate + Spring + Eclipse

Cognition is a new open source product similar in spirit to Trails. Both are approaches using Tapestry and Hibernate to streamline the process of creating a "typical" web application. Trails is very domain driven, creating the database schema from the object model. Cognition includes graphical editors inside Eclipse to build the schema, and derives the object model from the schema. There's a really impressive viewlet showing how to create a simple app really, really fast.

I can't wait for some time to open up in my schedule so I can give Rails, Trails and Cognition a spin.

Tuesday, March 28, 2006

HTML A tag vs. POST

Just an observation. If it is so damned important that GET operations be non-state changing and idempotent (blah blah caching, design of HTTP, firewalls, etc.) ... if it is so damned important that you never change anything expect using POST (and then send a redirect afterwards) ... tell me why the <a> tag does not support a METHOD attribute, the way <form> does. I mean, think back a few years, at all the crazy tags Netscape and Microsoft put into their browsers, and they miss this? Still?

I mean, this hasn't changed in years, and has consistently held web development hostage to the use of JavaScript to keep any non-trivial page from featuring a big old submit button. Apparently, the Powers That Be are afraid that without a big old submit button, we won't realize that hitting the "delete" key is going to delete something.

Sure JavaScript is all pervasive now, and you can force a form to submit using JavaScript ... and the use of Ajax will eventually mean that any non-trivial operation will be coded using XmlHttpRequest (which will do a post). Someday. For users with JavaScript enabled. But I just want to be able to write:

<a href=". . ." method="post">delete this report</a>

Monday, March 27, 2006

Tapestry Support Network Live Again

Woops. I accidentally let the domain registration for the Tapestry Support Network site lapse while I was on the road. All fixed now! Time to put some new content up there.

Sunday, March 26, 2006

New version of tapestry-spring

I've built out a new and improved version of tapestry-spring yesterday and today. This is a tiny module that properly initializes Tapestry to allow Spring beans to be injected into Tapestry pages.

This one works first off! I now run an integration test to prove this; it starts up a Jetty instance and injects a Spring bean into a Tapestry page.

More importantly, this version addresses the prototype issue. Using the standard @InjectObject annotation messes up when the bean being injected is not a singleton. Non-singleton Spring beans, aka prototypes, must be re-acquired from the BeanFactory in order to get the correct, new version.

There's now an @InjectSpring annotation that does that; reading the property will, beneath the covers, always go back to the BeanFactory to obtain a fresh copy. No caching at any layer, no problems.

I just realized that I forgot to update the documentation; that will come shortly.

I also bumped the version number up to 0.1.2 to celebrate the fact that this code works. But it is still alpha quality!

I did some trickery (I believe) so that the non-annotation classes are compiled for JDK 1.3, and the annotation classes are compiled for JDK 1.5. Took a bit of a struggle with Maven, but it works. If you aren't using annotations, you need to use a bit of XML:

<inject property="myProperty" type="spring" object="mySpringBean"/>

Static imports and Java language evolution

It's interesting to see the differences between how you expect to use a new language feature and how you end up really using it.

For example, of all the new features in 1.5, the idea of static imports seemed to be the least useful. From the outside, it looks like you get to say "min()" rather than "Math.min()". Big woop.

But what I've found when coding using static imports is a new clarity to my code. Once you strip away the class names from static methods the part that's left starts looking a lot like new and extensible language keywords.

For example, here's a test case from some code I'm working on.

    @Test
    public void test() throws Exception
    {
        Method m = ComponentFixture.class.getMethod("getSpringBean");

        EnhancementOperation op = newMock(EnhancementOperation.class);
        IComponentSpecification spec = newMock(IComponentSpecification.class);
        Location l = newMock(Location.class);
        Capturer c = newCapturer(InjectSpecification.class);

        spec.addInjectSpecification(capture(c));

        replay();

        new InjectSpringAnnotationWorker().performEnhancement(op, spec, m, l);

        verify();

        InjectSpecification is = c.getCaptured();

        assertEquals(is.getObject(), "someBeanName");
        assertEquals(is.getProperty(), "springBean");
        assertEquals(is.getType(), "spring");
        assertSame(is.getLocation(), l);
    }

What I've found as I've been coding is that I make extensive use of static imports. First of all, Eclipse makes it easy to do (Ctrl-Shift-M on top of a static method converts it to a static import). Secondly, my personal coding style has been to use a goodly number of static methods (if I can define a new feature in terms of the existing public API of an object, and I don't expect there to be a need for subclasses to override, then I create a static method that takes the object as a parameter).

Those assert calls at the end are actually static methods on an Assert class. Some of the other methods, newCapture() and capture(), are also static. The newMock() calls are inherited from a base class. It actually looks better inside Eclipse, because the static methods are italicized.

My point is ... the code is looking more expressive to me, as some clutter falls away. Autoboxing reduces some more clutter. So does the new for loop, and variable argument lists. Generics are still something of a wash (you get more self-describing code by adding lots of clutter, but you gain by removing explicit casts). The end result follows my motto, though: Less is More.

Has this transformed the language? No, and perhaps that's the point. It's some incremental change, but it's makes for some small steps in the right direction. It's not quite the fluid flow of static class methods in Ruby (used for all kinds of meta-programming), but it's still nice.

On the other hand, Sun is much less aggresive in adopting changes to Java than, say, Microsoft. I hate to say it, but innovation (where innovation is defined as adopting features that other languages have had for a decade or so) seems to be occuring in C# before Java. In some cases, it is occuring in other languages that execute on the Java VM. The end result is the same sad story of Sun chasing Microsoft's tail.

I'd like to see some real improvements to the language. I want Ruby blocks and continuations, C# autotype variables, built-in Aspect support and, hey, maybe something I don't know about that will make my programming life better (maybe a pervasive hot class reloader). In this respect, Java always feels like a perpetual bridesmaid, never a bride.

Saturday, March 25, 2006

NFJS Examples available

I've now been able to build and deploy the examples from my talks at No Fluff Just Stuff. The version number is still 0.0.1 and probably will be for some time. You can obtain a pre-compiled WAR, or a source distribution (with out without the PowerPoint slides) from http://howardlewisship.com/repository/com/howardlewisship/nfjs-tapestry/0.0.1/.

Huzzah! Subversion woes fixed.

I was just starting to panic. I was unable to check out my NFJS example code onto my desktop (it's stored using SVN, using my laptop as the SVN server). I've had some problems with Subversion recently, but thought I had resolved them.

From Eclipse, and from the command line, I was getting a wierd error:

bash-3.00$ svn update
svn: Can't read from connection: Software caused connection abort

From what I can tell, this occured when pulling down some large PowerPoint presentation files. Of course, there's no way to determine exactly what file the failure occured on, or why.

No output in the Subversion.log, or the svnserve command line, or any useful output from svn command line (or the Subclipse tool). Feedback anyone?

I tried updating to the latest Subclipse, 0.9.108. No help.

Finally, I tried upgrading my SVN server to 1.3.0 and ... things are working again!. Supposedly, I could have stayed with a Berkley DB repository using 1.3.0, but I've gone through the work of converting to a file system repository (as one of my attempts to resolve this problem), and I can't see the advantage of moving back. In fact, if anything, SVN seems faster or more responsive using the file system.

I should finally be able to get those NFJS examples up on the web site.

Friday, March 24, 2006

Back from the road! / tapestry-spring plans

Huzzah! Watch out Portland ... I'm back.

I actually had an exit row and room to work on the flight back from Phoenix. I decided to take another look at tapestry-spring.

First off, please remember that it is alpha code! So the fact that it completely doesn't work shouldn't be a total surprise. I had packaged the critical hivemodule.xml file under WEB-INF, not META-INF. Chalk it up to force of habit ... that's what you do for Tapestry applications, but this is a standalone library.

The reason I didn't catch that in my integration tests was ... I'm a lazy, lazy man. I need to learn how to write proper integration tests for tapestry-spring using Maven. I've actually had some good luck starting up Jetty inside a (TestNG) test case and that's the likely course I'll pursue.

So, that's half the story. The other half is dealing with Spring's prototype beans. This was someting that completely surprised me about Spring, once people started to complain. If you define a bean as having the prototype lifecycle, it means that you get a new instance everytime you ask the BeanFactory for it.

I really dislike that approach, because it puts the client code in charge of managing the lifecycle of the bean.

By contrast, HiveMind covers similar functionality quite differently. When you get a service from the Registry (the equivalent of getting a bean from the BeanFactory), you are going to get a proxy. Same service interface, different implementation (brewed up on the spot). The lifecycle of the service is hidden inside this proxy. You can share this proxy around, pass it between threads, even serialize and deserialize it (I think ... there's a few issues around that) and it just works.

The rough equivalent of Spring's non-singleton/prototype beans are HiveMind services with the threaded lifecycle. When you invoke a method on the proxy, it finds or creates a per-thread instance of the service. The per-thread instance is cleaned up and discarded at the end of the request (it's effectively built around a servlet request/response cycle).

This is used all over the place inside Tapestry. What's nice is that a piece of code can treat a proxy to a normal service, and a proxy to a per-thread service identically. That concern (in the AOP sense) is buried inside the proxy. Makes testing easier too.

Now, back to Tapestry's @InjectObject annotation. It's just broken for Spring prototype beans, because it's built around HiveMind's design, not Spring's. So it gets the object out of HiveMind just once and holds onto it, passing it into pages and components via a constructor (this is part of Tapestry's enhanced subclass approach to AOP).

For prototype beans, that means that we get the bean just once per component, and are stuck with it for any instances of that component we instantiate. The same bean instance, once aquired from Spring, will be passed into each new instance of a given page or component.

So ... I'm expanding tapestry-spring to add a specialized annotation, just for Spring. @InjectSpring will create a synthetic getter method that always gets a fresh instance of the named bean from the BeanFactory. That should solve the problem in its entirety.

I just need to stuggle with Maven a little bit more; I want to create a single JAR, where part of the code is compiled with JDK 1.3, but the annotation part is compiled with JDK 1.5. I think I can do this, by having multiple source roots (so src/main and src/annotations) and some extra compile executions.

Ultimately, this code may move under the Tapestry top-level project at Apache, once that gets set up. In the meantime, living at JavaForge is perfectly ok.

But, in the meantime, I need to catch up on the new Doctor Who, waiting for me on my Tivo. I've been out of town that long.

Sunday, March 19, 2006

NFJS code and slides ... just a little longer

It turns out I won't be able to post the updated slides and code from my No Fluff Just Stuff sessions because I left a critical password behind on my desktop. I'm on the road still (a long trip!) and will see about getting this stuff in place this coming weekend. Sorry for any inconvienience.

Friday, March 17, 2006

Zillow.com on The Boston Globe

Just noticed an article in The Boston Globe about Zillow.com. Zillow is a real-estate property values search application; at its core is a Flash application, but all the necessary infrastructure around that is Tapestry 4. I'm sure Ben and Dion are wondering why it's Flash and not Ajax.

Bitten by IE once again

If there was ever a single piece of software I hated with a passion, it would be Internet Explorer. I had let my seething resentment for this abomination settle for a while, as I do all my browing and development using FireFox.

However, with my project developer hat on, I have to support IE. My client, of course, is interested in IE support (given their user base, IE use will likely predominate). On just one page of my application, we hit the Operation Aborted error. The symptoms of this is that a page paritially loads, then a modal popup announces "Operation Aborted", and when you click OK, you are sent to the "This page cannot be displayed" page. I'm still tracking down the documentation, but it appears to be about a race condition where JavaScript modifies the DOM before IE is ready for it.

Now, I would have thought Tapestry would be safe from this, because of its approach to JavaScript ... the fact that JavaScript goes in proper places, at the top of the document, or at the bottom, rather than scattered throughout the document.

Doesn't matter; this page uses a DatePicker component, nested within a few tables for layout (a new reason why tables for layout is a bad approach) and apparently that's enough to trigger this bug in IE.

Side note: I talk a lot about the importance of Feedback, that tools should clearly identify problems and guide you to solutions. On a grading scale of A - F, IE would receive the grade take out back and put down like a rabid dog on this issue. And many others.

I have a couple of leads on this bug:

I'm going to see if using the Tacos DatePicker will work better than the built-in Tapestry DatePicker.

Update: The Tacos DatePicker did the job. Better yet, the latest DatePicker (from Tacos 4 beta 2) is simply stunning from both a visual and a useability perspective.

Tuesday, March 14, 2006

Wednesday, March 08, 2006

From the fanciful ideas category ...

I was just thinking about a kind of half-measure between normal Tapestry useage and Trails.

One of the tedious aspects of building a lot of web apps (using Tapestry) isn't the managing of data in and out of Hibernate or JDO, it's just the repetition of building a table, inside a form, with each row containing a FieldLabel and a TextField (or PropertySelection, or whatever).

Wouldn't it be nice if I could just plop the following into the middle of my form?

<span jwcid="@edit:EditObject" object="ognl:pojo"/>

And this magic EditObject component could build the rest for me? This, certainly, would leverage Trails code, or Trails-like code. I'm sure there would be additional parameters to control CSS, and to control which properties were to be editted. And, of course, some set of annotations to define the validation of those properties. Maybe even so carefully named Block components to provide row overrides? Again, very Trails.

I think this logic would kick ass when building prototypes.

I was just sending a reply to Matt Raible about Java web framework sweet spots. At the core of my response to why Ruby on Rails is gaining so much mind share is because its represents a solution, not a tool. The Java space, especially the open source crowd, has gotten really good a churning out extremely useful tools. However, we tend to leave the solutions to the motivated students. The lesson of Ruby on Rails is for us tool-makers to get fired up about creating solutions.

This is just the opposite of how Tapestry has evolved, which (of course) parallels the evolution of how my coding and design skills has evolved. Earliest Tapestry was a very pure tool, focused entirely on "animating" HTML tags, as well as the transient and persistent state management. Over time, the components evolved from a focus on a single tag to many tags, to entire behaviors (including early precursors to Ajax techniques). That's great, but it's been left to the imagination of the user to see how those tools fit together to allow you to create a useful application.

This is more than just a question of examples, it's really about the emphasis of the overall framework. "Here's how you edit your object (in one line)" should be the first thing new users see and learn ... giving the users the ability to exactly control the HTML should be lesson three or five or ten. That's where Trails is getting things very, very right.

Subversion: ouch!

So, all of a sudden, I'm having massive problems with my Subversion server. Basically, nothing works. I can't seem to check new files in (it appears to crash svnserve, resulting in broken pipe exceptions) and I also see problems checking files out.

I'm in the middle of a full backup of my laptop (before my big trip to Boston and then Tucson). I think, after that, I'll dump out my repository, and rebuild it as a file system (not Berkeley DB) version. I've heard people claim that SVN in server mode doesn't work well with Berkeley DB, but I had thought that was only when you have multiple users pounding on it.

This is frustrating, and bad timing. I'm concerned that I'll have data, or at least revisions, in SVN I can't access. We'll see. It's always something.

Anyway, this is why I haven't had a chance to update the code for the NFJS project to include the latest code and presentations. I can't get things into SVN so that I can properly build and deploy.

Update: It's possible that I have a bad sector on my hard drive (Acronis has found an unreadable sector ... it's impossible to say if this bad sector has anything to do with my Subversion repository). Either way, reading (if possible) the repository to a dump format, and building a new file-system repository, should be a reasonable approach.