Google has recently launched Google Health, a place where you can organize health information, keep it up to date and stay current with the latest health issues. We're happy to say that Google Health was built with the Google Web Toolkit, and pleased to have Samantha Lemonnier from the Health team share her experience using GWT.

Google Health started to pick up speed around the time I first joined Google. A few of us had whipped up a prototype in our 20% time. GWT naturally came into the picture as we tried to decide what we would use to build our client infrastructure: hand-written JavaScript with other internal JS libraries, or GWT. We didn't jump right to GWT until we did our homework. We loved the concept, but GWT was fairly new back then. We were cautious about whether it was mature enough for a production-planned project like Google Health.

Since many of you are faced with these same decisions, I thought it might be useful to share a synopsis of that first email thread I wrote to the GWT team titled "GWT, to use or not to use". In it I included a link to our mock as well as 4 key questions:

1. Can we use GWT to accomplish all that was in the mock?
2. How many browsers does GWT reliably support?
3. Is i18n supported?
4. How big is the GWT library that needs to be downloaded and how will it perform in the browser client?

Scott Blum from the GWT team responded that "in general anything you can do in HTML, you can do with GWT". Joel Webber, one of the founders of GWT, added "Looking at the your mocks... it appears as though you would want to fetch lots of information from the server during the course of interaction with the user, and to update both the form on the left and the results on the right interactively. I think GWT would be an excellent way to do this". To get a better feel for what GWT development meant, I created a sample project to test the waters. After exploring the widget library, I was able to build a functional prototype quickly. I tried a bunch of different widgets and found that they are easy to use and extend. The RPC calls were straightforward as well, and tied into the Servlet framework nicely. I was very pleased with the result of the prototyping.

Scott also confirmed browser support for "Recent versions of Opera, Safari, and Mozilla/Firefox; IE6+", which was satisfactory for us.

At the time, the i18n support was still in the works, but we were assured that it would arrive very soon. We were a little bit worried about how hard it would be but we were pleasantly surprised to learn that the implementation was really simple. All we had to do is to inherit the i18n package, create the constant and message classes along with their associated property files for all the strings, messages that need to be externalized.

The initial answer I got regarding our fourth question was "your entire application is monolithically compiled into aggressively optimized and obfuscated JavaScript. It's a "pay-as-you-go" model, code you don't call gets pruned", and "GWT uses a trick to allow its script to be reliably compressed, resulting in a 3-5 fold decrease in size". I had vivid memory of working on scripts to prune and obfuscate handwritten JavaScript code in my previous job, and how it required constant tweaks and tune-ups. As painful as it may be, performance tuning is a very important step for any large-scale JavaScript application. The initial download time and execution speed are crucial and greatly affect the user's perception of an application. As a skeptical engineer, I performed my own tests to validate these claims and test performance, initially and prior to launch, to make sure that the code was pruned, optimized and obfuscated. The results of this testing proved to me that GWT could live up to our expectations.

Finally, after receiving convincing arguments and techniques for creating a custom-cut Google Data library, the choice for which technology to use to bring Google Health to production was obvious, and the rest is history. My sample GWT project became the launch pad for the Google Health client infrastructure.

Of course we didn't develop the whole application without running into technical challenges. We grew our application as GWT itself was still growing up. There were times when we realized that some of the little details in JavaScript were not exposed through GWT. In most of these cases, we used JSNI to access lower level JavaScript functionality. At one point, we also noticed that as we continued to build the application the initial download time started growing as well. We analyzed all the requests and realized that there was cumulative latency introduced by each little icon, logo and other images that needed to be requested and loaded during the application loading. We used GWT image bundle to handle all the images and it considerably improved performance. Finally, in cases where we thought a certain widget should be further extended, we took one of a few approaches: first we checked for such a widget in the GWT pipeline; second we checked the developer forum to see if someone has already constructed what we need and contributed it back the open source community; third, we developed our own and contribute it back to GWT for potential inclusion in a future release.

Looking back today at a successful Google Health pilot and public launch after 2 major UI redesigns, numerous UI experiments including proof of concepts and user studies, it's hard for me to imagine accomplishing so much in last two years without GWT. We were able to do all the fancy JavaScript stuff in half of the effort it would have taken with handwritten JavaScript. We were able to write truly object-oriented UI code, refactoring and reuse were much easier, and leveraging IDEs like IntelliJ or Eclipse made UI redesigns much easier to absorb. GWT's compile-time elimination of dead code also meant we didn't have to worry about unused code that was still hanging around the codebase (of course it's best to do code cleanups every now and then), and we were also able to easily create unit tests for our UI code with GWT's integration with JUnit, which saved us lots of debugging time as our engineering team grew. It's been an amazing experience.

The next and hopefully last release candidate for GWT 1.5 is almost upon us. In anticipation, we'd like to really crank up the excitement level and, well, the sheer geek factor of this here blog.

If you are new to GWT, you may be wondering what all the excitement is about. Why is GWT different from other framework-style solutions? GWT is more of a tool chain and a baseline technology rather than a particular application framework. So, although GWT has lots of libraries, you can use as many or as few as you find useful. Don't like GWT's UI? You can build your own using the DOM classes. Want to use JSON instead of RPC? It's easy. In fact, it is completely possible to start from scratch and build your own framework using GWT and benefit just as much from GWT's overall approach to debugging and compilation.

So, high-level, why should you consider using GWT for your next big web app?

1. Ajax applications, when designed well, can by their nature provide a much better user experience than server-centric approaches for many important kinds of applications. Since you are reading this blog, you probably already know this.
2. The GWT compiler frequently produces smaller, faster JavaScript than you would write by hand.
3. You can be more productive developing with GWT and, simultaneously, the JavaScript you deploy to users will be more reliable.
4. You get the opportunity to say "Gwit" a lot.

We doubt you are someone who is easily influenced by mere assertions or marketing pitches, so we've put together the next few blog posts to take a look at exactly how GWT achieves these performance gains, and how it makes working with JavaScript easier.

Before we dive into the technical details, one last note. We sometimes get asked two questions about the very nature of GWT:

1. Why does GWT center on the Java language and tools?
2. Isn't GWT heavyweight and limiting compared to handwritten JavaScript?

In answer to the first, understand that our goal and our passion is to radically improve the end user experience of the web, which means that GWT must produce JavaScript that is maximally performant and reliable. In order to do that, we naturally want to apply a lot of optimizations to source code and catch bugs as early as possible. Both of these goals are directly facilitated by Java's static type system and the existence of great Java IDEs. That is why we, dispassionately, chose to center GWT on Java technologies. That's it — no fodder for language wars here.

In answer to the second, it is perfectly reasonable that some developers, upon first hearing about GWT, assume that it is a sort of "walled garden of abstraction" that forever locks you into Java development and prevents you from using or integrating with handwritten JavaScript. Nothing could be further from the truth, which is a great segue...

GWT's JavaScript Native Interface (JSNI)

You can easily combine handwritten JavaScript directly into GWT code. It's all JavaScript in the end, of course, so why not allow GWT developers to mix-and-match in any way that's useful? That's what JSNI is all about. It's named similarly to the Java Native Interface (JNI) because it uses the same basic idea: declare a Java method "native" and then use another language to implement it. In the case of JSNI, that other language is JavaScript.

Writing Java methods with JavaScript

JSNI is useful to create a reusable abstraction on top of functionality that is most naturally expressed using JavaScript syntax rather than Java syntax. For example, regular expressions are pleasantly concise in JavaScript, so you can use JSNI to make them directly available in your GWT code. Suppose you wanted a method to flip someone's name around such that their last name comes first, for example turning "Freeland Abbott" into "Abbott, Freeland". (Admittedly, this example is an I18N nightmare.) You can create a short JSNI method to do this:

// Java method declaration...
native String flipName(String name) /*-{

  // ...implemented with JavaScript
  var re = /(\w+)\s(\w+)/;
  return name.replace(re, '$2, $1');

}-*/;

Notice that the method body is really just a glorified Java comment, enclosed by the special tokens /*-{ and }-*/.

Calling Java methods from JSNI

You can go the other direction, too, calling a Java method from JavaScript. Suppose we modified the example above to invoke a callback instead:

package org.example.foo;
public class Flipper {

  public native void flipName(String name) /*-{
    var re = /(\w+)\s(\w+)/;
    var s = name.replace(re, '$2, $1');
    this.@org.example.foo.Flipper::onFlip(Ljava/lang/String;)(s);
  }-*/;

  private void onFlip(String flippedName) {
    // do something useful with the flipped name
  }
}

Using JSNI to access external JavaScript code

Naturally, you can access any sort of external JavaScript code from within a GWT module. For example, if your HTML page looks like this:

<html>
  <head>
    <script>
    function sayHello(name) {
        alert("Hello from JavaScript, " + name);
    }
    </script>
    
    <-- Include the GWT module called "Spiffy" -->
    <script src="org.example.yourcode.Spiffy.nocache.js"></script>
  </head>
...

Within your Java source, you can access the sayHello() JS function through JSNI:

// A Java method using JSNI
native void sayHelloInJava(String name) /*-{
  $wnd.sayHello(name); // $wnd is a JSNI synonym for 'window'
}-*/;

The GWT compiler inlines the extra method call away, so calling the sayHelloInJava() method in your Java source is no more expensive than calling sayHello() directly from handwritten JavaScript.

Creating JavaScript libraries with GWT

You can even create JavaScript-callable libraries from your GWT code. This is a pretty neat trick:

package org.example.yourcode.format.client;
public class DateFormatterLib implements EntryPoint {

  // Expose the following method into JavaScript.
  private static String formatAsCurrency(double x) {
    return NumberFormat.getCurrencyFormat().format(x);
  }

  // Set up the JS-callable signature as a global JS function.
  private native void publish() /*-{
    $wnd.formatAsCurrency = 
      @org.example.yourcode.format.client.DateFormatterLib::formatAsCurrency(D);
  }-*/;

  // Auto-publish the method into JS when the GWT module loads.
  public void onModuleLoad() {
    publish();
  }
}

You can then access this GWT-created functionality from within any HTML page or another JavaScript library:

<html>
  <head>
  
    <-- Include the GWT module that publishes the JS API -->
    <script src="org.example.yourcode.FormatLib.nocache.js"></script>

    <-- Write some JS that uses that GWT code -->
    <script>
    function doStuff() {
      alert(formatAsCurrency(1530281));
    }
    </script>
  </head>
...

Ray Cromwell (of GWT Extreme! fame, among other things) has taken the above JavaScript publishing technique to the extreme with his GWT Exporter project. It creates all the publishing code automagically using GWT's compile-time code generation facility. (Does "compile-time code generation" sound cool? If so, stay tuned for the upcoming posts in this series.)

Putting it all together

Using JSNI, you can freely mix handwritten JavaScript, external JavaScript libraries, and Java source code in any way that you need to. That's what we mean we say GWT isn't a walled garden of abstraction and that you can adopt GWT incrementally into existing web apps. And, best of all, you can debug all the Java code using the Java debugger of your choice.

To learn more, check out JavaScript Native Interface in the GWT Developer Guide. Better yet, let GWT compiler architect Scott Blum explain it to you himself.

As you may know, the Google I/O conference came to town last month and saw excited developers and lots of great sessions. It was a blast, and I had the pleasure of meeting some of our developer community members in person, which for me was the icing on the cake. Thanks to all who came to the event!

For those of you who may have missed the Google I/O conference, we're happy to report that the presentations and slide decks have been posted and are now viewable online!

You can check out the full presentation playlist here. We've also created a GWT session playlist if you're only interested in GWT-related material.

Here are some recommendations for sessions you might enjoy:

• New to GWT 1.5? Let Bruce show you how to do nifty DOM programming using new featuresintroduced in the latest release of GWT in "Surprisingly Rockin' JavaScript and DOM Programming in GWT".
• What allows applications built on GWT to be so high performance? One of the answers to this question is Deferred Binding. Bruce once again gives you the lowdown on how the technique is employed in GWT in "Faster-than-possible code: Deferred Binding in GWT".
• Ever wanted to mashup your application with other Google APIs? The Google API Libraries for GWT is designed for that purpose, and Miguel shows you how to use it in "Reusing Google APIs in GWT".
• Are you a GWT pro, and are looking for the next big thing in GWT technology? Check out "GWT Extreme!", presented by Ray Cromwell, who shows just how far you can go with GWT (from GWTQuery to GWT for Android, and beyond!)
• So you've built your fancy new user interface in GWT, but now how do you get your application to talk to a server? As with most things in GWT, you have options. For an overview of what's available and recommended best practices, Miguel provides an overview "GWT and Client-Server Communication"
• You've built your application in GWT and it now has some nice out-of-the-box optimizations. You're done with performance improvements, right? Well, why stop at fast when you can make your app really fast? GWT provides even more ways to keep boosting your application performance using ResourceBundles. You can also customize your application's startup using the new Linker subsystem. For more information on harnessing these techniques, check out Bob Vawter's talk "Resource Bundles and Linkers in GWT".

Enjoy!

I'm excited to report that there are some fresh new links on our download page leading to a release candidate of Google Web Toolkit 1.5.

Since the previous release of GWT, we've seen a lot of really great applications that demonstrate what is possible when you are able to focus on the user and stop worrying so much about browser quirks and other Ajax obstacles. Inspired by what we have seen so far, we have continued to concentrate our efforts on enabling developers to use their existing tools to create web apps that users enjoy. GWT 1.5 takes this commitment even further with exciting new features and over 150 bug fixes. And, like all GWT releases, most of the benefits are just an upgrade-and-recompile away.

We've gotten very positive feedback from early adopters and here is what they are most excited about:

Java 5 language support
It feels good to finally close out our most requested feature. GWT developers can now freely use the modern Java syntax including generics, enumerated types, annotations, auto-boxing, and so on.

New compiler optimizations increase performance
With this release of GWT, we're happy to announce that our compiler produces faster code than you would write by hand! How's that? A bunch of new compiler optimizations allow us to efficiently inline method calls, even through many layers of indirection. Translation: all the nice abstractions and clean design work that are essential to maintaining a large code base melt away in the compiler's output, giving your users the fastest possible experience. By contrast, if you were writing JavaScript by hand, you'd have to choose between writing good code and writing fast code ��� and when your application got to a certain size, maintainability would make the second choice impossible. With GWT 1.5, you don't have to compromise; just write good code and let the compiler make it fast.

JavaScript Overlay Types
This further enhances GWT's interoperability with the underlying JavaScript layer. ���Overlay type��� is a new term we're using to describe the ability to model JavaScript objects as strongly-typed Java instances with no additional runtime cost. Overlay types make it easy to provide fine-grained interop with handwritten JavaScript libraries as well as providing an optimal way to make JSON structures directly accessible to GWT code.

High-performance DOM API
Up until GWT 1.5, we've concentrated mostly on Widget-level APIs, and until the advent of overlay types (above), direct DOM programming wasn't particularly convenient. GWT 1.5 goes beyond "convenient" and well into "elegant" with an entirely new DOM API that enables type-safe, low-level DOM programming that will be both comfortable to DOM experts and free of any runtime overhead.

Default visual themes
Several default visual themes are now available by default so that developers get an attractive UI out of the box and have a good starting point to create their own custom styles in CSS.

To find out more, download the release candidate and join us in our mission to radically improve the web experience for users. And as always, we are eager to hear what you think so feel free to give us feedback in the GWT Developer Forum.

With Google I/O just a few weeks away (May 28 - 29), if you haven't already registered, now's a good time to do so. There are now over 80 sessions posted, including a lot on Google Web Toolkit. In fact, there's a GWT session during just about every time slot over the two days. A few GWT sessions which we've recently added include:

Using GWT to build a high performance collaborative diagramming tool
You may have seen us write about Lombardi Blueprint before. Lombardi has built an amazing user interface and experience using GWT. Hear from Alex Moffat and Damon Lunden from Lombardi as they focus in on two challenges they faced: efficient rendering of the diagrams in the browser and client/server object syncing for multi-user editing.

GWT Extreme!
Ray Cromwell, CTO of Timepedia.org, has been doing some really interesting things with his Syndroid project, a combined GWT and Android exploration. Ray will be showing the power of using GWT and linkers to create native interfaces into ActionScript, Android, Gears, and more.

The conference promises to be educational and a lot of fun. I'm particularly excited that my favorite (although fourth most popular) digi-folk parody band will be making an appearance. We'll also have a number of engineers from the GWT team traveling out from Atlanta, so come say hello.

Be sure to visit the website to see the complete list of sessions and to register. For those coming from out of town, there are discounted room rates at nearby hotels. Read the details on the website to take advantage of the discount, but move fast because the hotel discount ends tomorrow, May 6th.