Google Web Toolkit. (GWT). Sang Shin. Java Technology Architect & Evangelist. Sun Microsystems, Inc. When you deploy your GWT applications to production, you deploy this JavaScript and .. Slides from Presentation at TSSJS (PDF). Download Eclipse, install Google plugin and GWT SDK. framework for creating Ajax-enabled web applications in Java. It's open source, completely. Life before GWT. Dynamic web applications are typically written in several differ- Google Web Toolkit unifies client and server code into a single appli-.

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rich internet applications with the Google Web Toolkit. including the library, which gives the user the opportunity to read PDF files. Accelerated GWT - Building Enterprise Google Web Toolkit Applications .. Google Web Toolkit (GWT) to generate optimized. JavaScript and avoid the dreaded. Production mode (R-click, Google → GWT Compile) import*; New apps contain sample files that are good examples to learn.

Of course, you also can use AJAX explicitly for any special purposes you might have. What Is the Google Web Toolkit?

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Its first public appearance was in May at the JavaOne conference. Currently at the time of this writing , version 1. It is licensed mainly under the Apache 2. Don't confuse JavaScript with Java; despite the name, the languages are unrelated, and the similarities come from some common roots.

Instead of using the JavaScript language which is powerful, but lacking in areas like modularity and testing features, making the development of large-scale systems more difficult , you code using the Java language, which GWT compiles into optimized, tight JavaScript code.

Moreover, plenty of software tools exist to help you write Java code, which you now will be able to use for testing, refactoring, documenting and reusing—all these things have become a reality for Web applications.

Don't worry about localization matters either; with GWT, it's easy to produce locale-specific versions of code. There's another welcome bonus too. GWT takes care of the differences between browsers, so you don't have to spend time writing the same code in different ways to please the particular quirks of each browser. Typically, if you just code away and don't pay attention to those small details, your site will end up looking fine in, say, Mozilla Firefox, but won't work at all in Internet Explorer or Safari.

Part 1 Getting started

This is a well-known classic Web development problem, and it's wise to plan for compatibility tests before releasing any site. GWT lets you forget about those problems and focus on the task instead. According to its developers, GWT produces high-quality code that matches and probably surpasses the quality size and speed of handwritten JavaScript.

By default, the end code is mostly unreadable being geared toward the browser, not a snooping user , but if you have any problems, you can ask for more legible code so you can understand the relationship between your Java code and the produced JavaScript.

A development environment—Google's own developers use Eclipse, so you might want to follow suit. GWT itself weighs in at about 27MB; after downloading it, extract it anywhere you like with tar jxf.. No further installation steps are required. You can use GWT from any directory. For this article, I used Eclipse.

Before starting a project, you should understand the four components of GWT: When you are developing an application, GWT runs in hosted mode and provides a Web browser and an embedded Tomcat Web server , which allows you to test your Java application the same way your end users would see it.

Note that you will be able to use the interactive debugging facilities of your development suite, so you can forget about placing alert commands in JavaScript code.

To help you build an interface, there is a Web interface library, which lets you create and use Web browser widgets, such as labels, text boxes, radio buttons and so on. You will do your Java programming using those widgets, and the compilation process will transform them into HTML-equivalent ones. Because what runs in the client's browser is JavaScript, there needs to be a Java emulation library, which provides JavaScript-equivalent implementations of the most common Java standard classes.

Note that not all of Java is available, and there are restrictions as to which classes you can use.

It's possible that you will have to roll your own code if you want to use an unavailable class. As of version 1.

In addition, as of version 1. Finally, in order to deploy your application, there is a Java-to-JavaScript compiler translator , which you will use to produce the final Web code. If you are like most programmers, you probably will be wondering about your converted application's performance. However, GWT generates ultra-compact code that can be compressed and cached further, so end users will download a few dozen kilobytes of end code, only once.

Furthermore, with version 1. Finally, because you won't need to waste time doing debugging for every existing Web browser, you will have more time for application development itself, which lets you produce more features and better applications. Packages Using GWT requires learning about several packages.

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The most important ones are: com. You will need it if you are developing a system that will be available in several languages. You certainly will use these. GWT allows you to call server code transparently, as if the client were residing in the same machine as the server. You can find information on these and other packages on-line, at google-web-toolkit. Creating a new project is done with the command line rather than from inside Eclipse.

Create a directory for your project, and cd to it. Do not check the Copy Projects into Workspace box so that the project will be left at the directory you created.

After doing this, you will be able to edit both the HTML and Java code, add new classes and test your program in hosted mode, as described earlier. When you are satisfied with the final product, you can compile it an appropriate script was generated when you created the original project and deploy it to your Web server.

Let's do an example mashup. We're going to have a text field, the user will type something there, and we will query a server okay, with only one server, it's not much of a mashup, but the concept can be extended easily and show the returned data. Of course, for a real-world application, we wouldn't display the raw data, but rather do further processing on it. The example project itself will be called exampleproject, and its entry point will be example, see Listing 1 and Figure 1.

Figure 1. The recently imported project—the code just shows a welcome message. Listing 1. Projects must be created by hand, outside Eclipse, and imported into it later.

Two windows will appear: the development shell and the wrapper HTML window, a special version of the Mozilla browser. If you do any code changes, you won't have to close them and relaunch the application. The interface method should return a string with the name i.

GWT Tutorial

Implement the servlet code according to the code presented in listing 4, depending on the boolean parameter "isScript". On the client side: Listing 4 shows an example where the interface method is called createSummaryPDF. The string returned from the servlet is "summary. Consistent with the Perl philosophy of "There's more than one way to do it", I do not claim that this is the only way to handle this case, but it currently works fine for me.

Please note that before starting your application in hosted mode, you have to create at least a dummy "summary. But with GWT you have another choice. No longer does the server have to be a "web" service that only supplies HTML content. Using GWT RPC the server now supports services - implemented by servlets in our case - that only supply structured data. Figure 5 shows a slide that reviews the changes. But it was a rather nasty job, and I looked for another option.

So, after seeing Bruce's presentation I decided to redesign the whole application to follow his mantra: All client But that step required changing all my RPC interfaces, my caching strategies, and last but not least, all my servlets. Therefore my recommendation is: Consider early on where to put session and state management, and give Bruce Johnson's recipe a chance.

It pays at the end.

Because of this decision I had more communication between client objects. So I used the well-known GoF mediator pattern.

However, we have some JDK 1. Therefore I re-implemented the PropertyChangeEvent class and the mediator support to handle listener registration and message broadcast. Please contact me, if you are interested in the mediator part of the system.

Selenium see Resources is an open source tool that enables you to easily test web applications that contain rich, client-side, interactive content. So it is an ideal candidate for testing an Ajax application like the one you have created with GWT.

That has been described in about every serious publication about GWT. Therefore I will draw your attention to Selenium because I found it easy to use at least its IDE , powerful, and, last but not least, it has a lot in common with JUnit. Every action may be followed by a JUnit-like "assert" command that verifies some text on a page etc. These commands -- together with the "pause" commands -- are substantial when it comes to testing Ajax applications.

When you are satisfied with your tests you can even generate JUnit Java test classes out of Selenium's proprietary test format. In the IDE screenshot you can see "pause" and "waitFor" commands as well as assertions that could be verified in the test run marked green or that failed marked red. Of course that's only a small part of the tests you can do with Selenium, e. It's truly great, trying out your application in GWT hosted mode, but the real power of GWT comes when deploying your application to an application server or servlet container like Tomcat.

In this step you need to create a "war" file that should be copied automatically to your Tomcat "webapps" destination. Of course, you can do all the necessary preparation, compilation, copy and other tasks with Ant and ant-contrib, and, indeed, that was how I started.This would be the ultimate phishing.

Simply click Refresh, and you will be running the newer version of your code. Of course, for GWT, this is a bit of a bother, because it means that a client application cannot simply connect to any other server or Web service to get data from it.

He is particularly interested in the better security and performance of Linux boxes. Tutorial series: Examining different polling techniques As I mentioned before, I started with a familiar Ant script.

Your client calls the proxy, and the proxy calls the service. After doing this, you will be able to edit both the HTML and Java code, add new classes and test your program in hosted mode, as described earlier. So, after seeing Bruce's presentation I decided to redesign the whole application to follow his mantra: