Hardcore GWT Hands on Training?

It's the new year, and I've been mulling an idea recently that I'd like to get some feedback on from the community.

The GWT Conference was a blast, and it appears my Deferred Binding presentation was well received. Since then, a number of people have encouraged me to offer some sort of training or mentoring for GWT, either in classrooms, or in the form of corporate on-site training. I hesitate to get too distracted from working on Chronoscope and Timepedia, but after thinking about it some more, I do think it might be worth pursuing, perhaps one 2-day course per month.

What I don't want to do is some token GWT course that glosses over the core of GWT and shows one how to create some cute widgets and stuff them into a web page, without understanding what's going on under the hood. Rather, I'd like to teach, on Day 1, GWT from the ground up exploring in detail what is happening: Java vs JS Output, Deferred Binding, JSNI, Widget attachment, Widget event processing, RPC/Serialization vs On-the-wire representation, the Bootstrap/Selection process, Hosted Mode, debugging, testing, etc.

On Day 2, I'd then delve into more idiomatic patterns: Creating custom widgets, creating your own modules/libraries, Localization, image bundles, integrating with back-end frameworks, RPC and RPC customization, optimizing size and speed, etc

I'd require people to write code in short labs during the class, give personal help in troubleshooting, setting up Eclipse/IDEA/Netbeans environments, and ask that others who have completed labs successfully help participate in helping those having trouble, because I believe a good way to learn something is by in-class participation and trying to help someone else. Who knows, it might be a fun, campfire type atmosphere!

I'd risk losing a lot of newbies doing this, and also risk not getting any advanced users who are self-taught, but hopefully, there are a lot of people in the middle with some GWT experience, who would like a more in depth tutorial hands on. Perhaps I'd do a more marketing oriented/newbie introductory course later.

Ultimately, I'd hope that people who come away from the classes with not only enough knowledge to write code to cover their own use cases, but also have enough knowledge to fix bugs and contribute to GWT itself. The GWT compiler and core libraries should no longer be 'magic' to those taking the course.

Obviously, the course wouldn't be free, especially in offsite training where I'd have to rent the event space and also given the opportunity cost for me, but I would offer discounts if space is donated, charge less for the first 'beta' class, and given some steep student discounts, especially if students would arrive early and help me with class setup.

I'm working out the course material at the moment, and pricing out some meeting spaces. I haven't decided on a per-student price yet, but feel free to email me suggestions, course ideas, and most importantly, whether or not you'd be interested in attending, or your company would. Private replies can be sent to cromwellian / gmail.com

Oh, this would be for the SF Bay Area, hopefully BART/Caltrain accessible.

-Ray

Erratum for GWT Demystified

I noticed a small mistake in the first GWT Demystified article. I was performing some code metrics today and noticed my size estimates for the source base were off by a factor of 2x. When I posted the initial article, the 30 KLOC figure seemed funny, but I let it slide because it was the right order-of-magnitude, and I thought maybe I had generated more boilerplate with my IDE than I realized. (Copy Javadoc checkbox works wonders for KLOC)

What happened is I have a Maven2 build for Chronoscope and I had executed a command like "find chronoscope -name '*.java' -exec cat '{}' \; | wc -l" without running a clean first, and therefore, all the source got counted twice because it gets copied to the 'target' build directory under my project directory as well. (You do this, because GWT artifacts must include the source code if other projects are inheriting the Chronoscope module)

The actual figures are around 15KLOC, 1.5M source, 800k byte code.

Mea Culpa,
-Ray

GWT Demystified: Generators, Part 1

Why do at runtime what you can do at compile time?

If GWT had a mantra, this would be it.

Introduction

As I mentioned in the previous article, the GWT compiler deals with a closed world -- no dynamic class loading, but it does permit deferment of binding decisions until compile time via a rule based mechanism that is part of the external GWT Module metadata. You can choose to replace a given type with other preauthored types, or, and here's the important part: you can replace types with classes that are generated on the fly.

This is the compile time equivalent of what you would do at runtime with libraries like CGLIB or the JDK's Proxy/Interceptor classes, and similar to Sun's APT (Annotation Processing Tool), except that it's all integrated into GWT and you don't need to worry about running separate APT-passes.

The deferred binding mechanism is used heavily in GWT to replace standard implementations of browser widgets with quirky implementations for browsers with divergent behavior. GWT then compiles multiple permutations of your code base, running the binding rules separately for each browser. Thus, if you have rules to target 4 different browsers, you end up with GWT compiling 4 different code bases and producing 4 compiled outputs.

Why does it do this? Because the result is more optimal code. Otherwise, you would have to include all 4 Implementation subclasses in your main code base, and use runtime logic to dynamically call the appropriate target, e.g. "if(brokenDom) DOMImplIE.foo(), else... DOMImplStandard.foo()..." It shortens load time by only forcing your browser to load what is neccessary, and it shortens run time by removing another level of indirection. Finally, it permits the optimizer to actually inline the appropriate implementation directly into the call site.

Generators

GWT also uses compile time generation of Java code to implement many platform features. The most famous of course is the RPC/Serialization mechanism. Here, GWT takes an interface, such as MyServiceAsync, and generates an implementation of this class on the fly, which contains all of the logic needed to serialize non-primitive types, send them across the wire via XMLHttpRequest, invoke the RemoteService, deserialize the rule, and invoke the async handler. It is probably the most complex generator in GWT, but not the only one.

Internationalization and Localization are also handled by the generator mechanism. Instead of loading ResourceBundles at runtime, you instead pre-process them and turn them into an interface, with one method per property. GWT will then use a generator to fill in the implementation of this interface which returns the values that are in the property file when the corresponding method is invoked. And what if you don't use some of the properties? The GWT compiler will remove any unused (uncalled) properties from the compiled application, and the number of HTTP requests is reduced because the locale data is bundled inline with your code.

Finally, truly the coolest and most innovative application of generators to date is the ImageBundle. In the world of 3D graphics programming, there is a technique called Texture Atlas, wherein you combine many textures into a single large texture, because on many graphics accelerators, changing pipeline state, such as binding a new texture before drawing geometry, is an expensive operation or may stall the pipeline. A program using texture atlases instead, binds one or more mondo-big textures, and simply uses texture coordinate manipulations to render portions of them as needed.

GWT 1.4 uses a similar technique to reduce load times and network traffic. With ImageBundle, like the I18N mechanism, you create an interface with a bunch of methods, one for each Image, as well as metadata annotations telling the GWT compiler which image file on disk you want returned by the method. Then, at compile time, the GWT compiler combines all of the images together into one large image file and generates an implementation class to return, essentially, the bounding box location of where each image is located within the overall atlas. Finally, when drawing the images, you just draw the same image (the large one) over and over, but use clipping rectangles to show only the part which corresponds to the image you need.

This reduces the number of HTTP requests drastically, speeds up startup time, and also centralizes media resources to a factory. The I18N and ImageBundle technique may even be combined to produce localized image bundles.

You're starting to imagine the possibilities?

How about buttons rendered with drop-shadows? Rounded corners done at compile time? Object-relational mapping to Google Gears or serialized RowSets? Type-safe JSON wrappers?

The project that I have created as my first generator is one designed specifically to suit my needs. Chronoscope has a JavaScript API that allows pure JS developers to access functionality provided in GWT classes. The way it does this is by creating what I call "bridge" classes and methods in the top level browser namespace. These bridge classes contain the public names (non-obfuscated) of GWT methods that will be invoked by the Javascript-to-Java JSNI Mechanism.

The problem is, everytime I added a method to one of my GWT classes, I had to go write a bridge method for it, and as Chronoscope grew in size and complexity, I needed a more automatic, and safe, mechanism for exporting an external JS interface.

In part 2 of this article, I will take you step by step, how to write this GWT Exporter, with actual code, culminating with the drop of the code on http://code.google.com/p/gwt-exporter/


-Ray

GWT Demystified

This will be a first in a series of tutorials and essays digging deeper into some of the more esoteric (but extremely important!) functionality of the Google Web Toolkit. (This article is written by Ray Cromwell, CTO) I will be talking about some of the nitty gritty details of the GWT compiler, how to create your own custom generators and the cool stuff you can do with them, and finally, how to plugin new optimization algorithms into the GWT compiler itself.

The Google Web Toolkit can be considered a package of three fundamental technologies: The Java to Javascript Compiler, the runtime library/APIs, and the Hosted Mode browser. All three are very important components of GWT in their own right, but because the APIs and the Hosted browser are the most visual pieces (you can SEE THEM operating) they tend to have more impact on people, while the real heavy duty stuff being done by the GWT compiler goes mostly unnoticed.

This is why I am not surprised that many language zealots engaged in language wars often appear grimaced when I tell them I am rewriting my Javascript code in GWT. "Huh!? Why!?" Then the inevitable signs of misunderstanding crop up: "Didn't applets show running Java in the browser is slow?", "Doesn't GWT produce bloated code?", etc. Now, I am by no means a zealot for the Java language, but there does appear to be frequent misunderstandings about what the GWT Compiler is, and does.

The GWT Compiler is a real compiler. Not a simple translator that walks an abstract syntax tree turning Java expressions and statements into the nearest Javascript equivalents. In fact, the GWT Compiler performs optimizations that are very hard to do statically on raw Javascript, and hard to do even in regular Java.

For example, static dead code elimination is very hard to do safely in Javascript, and limited in Java as well (at the bytecode level). You can never really be sure that a public method in Java won't be called, because of dynamic class loading, and frankly, you can't even be sure that private methods won't be invoked due to reflection and interception techniques, thus the only safe way to do dead code elimination is to defer it to runtime and let Hotspot deal with it.

In contrast, GWT has very good information on which methods are reachable, and is extremely aggressive at removing unused methods, saving both bandwidth and start up time. The closest equivalent in the Java world would be MIDLets, since the same sorts of closed-world assumptions can be made.

GWT does more than just remove dead code. It performs inlining, polymorphic-to-monomorphic call conversion (devirtualization), a form of type-inferencing which GWT calls Type-Tightening (GWT can infer that a field of type Animal is only ever assigned type Cat. In fact, it can infer that such a field is always null!), and lots of other little tricks. It doesn't appear to have common subexpression elimination, copy propagation, or in-block dead code elimination yet, but in my third tutorial, I will demonstrate a simple naive way to achieve this.

What this means is that in GWT, you don't pay much for what you don't use, and you don't have to worry about figuring out what's used. It means GWT's Javascript output is not bloated. It has a constant factor overhead related to the bootstrap process, but as your applications grow bigger, this code becomes smaller.

The GWT compiler already does a good job producing compact javascript code (Chronoscope is 30,000 lines of Java, 3.2 Megabytes of source, 1.9 Megabyte of compiled byte code, and 137k of Javascript after GWT 1.4 compiles it, and 45k after gzip -9), and there is a lot of headroom still left in terms of optimization that it can do.

So why do I use GWT? Besides the fact that we want to run in environments that don't have Javascript, GWT's Hosted Mode is extremely helpful providing full access to the universe of Java debuggers, and automatic code completion and popup Javadoc is very nice. (Even though I use IntelliJ IDEA, which already has good Javascript code completion and popup documentation)

GWT is a good platform for building AJAX/RIA applications and allows one to easily port or repurpose existing Java codebases and tools -- another good option for developers. It has a bright future ahead of it.

-Ray
Coming up: GWT Generators HOW-TO: generate classes on the fly at compile time.

Timepedia @ Google Developer Day

We had a blast at Google Developer Day, especially meeting and hanging out with the Google Web Toolkit team. Google's organization of the event was excellent, and they are to be commended for staging a world wide event (free) for developers, providing ample (and good) food and snacks, as well as busing developers to the Google campus for an after hours party. We've been to freebie events before, and they haven't been this good.

At Dev Day, Timepedia launched a preview of one of our components: Chronoscope, which is our visualization platform for timeseries data written in GWT.

We got alot of positive feedback, and had fun hearing people try and guess what our t-shirts meant. Actually, we were surprised how many people got very close. Timepedia has been our personal hobby, our passion, for over two years, and we are both nervous and excited to finally reveal it to the public.

As we come closer and closer to launch time, we'll post developer notes, stumbling blocks, hurdles leaped, and give more information about some of the other pieces of Timepedia (such as codenames: Tardis, Timelord, Geisser, Everett, and Jarocki :) )