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Google Web Toolkit

Google Web Toolkit. Dudeanu Ermoghen Ibănescu Diana Melinte Laurenţiu - Ionuţ Petrişor Ionuţ Cătălin. Evolution of applications. 1960 – Mainframes, punch cards, monochrome text terminals; Same application, different code , one for every operating system - big development cost;

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Google Web Toolkit

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  1. Google Web Toolkit DudeanuErmoghen Ibănescu Diana Melinte Laurenţiu-Ionuţ Petrişor Ionuţ Cătălin

  2. Evolution of applications • 1960 – Mainframes, punch cards, monochrome text terminals; • Same application, different code , one for every operating system - big development cost; • Client/Server Applications • WIMP(Windows, Icon, Menu, Pointer); • Applications running on a desktop machine, with centralized data on a server • Bigger cost, because the client has to run on every operating system; an upgrade to the system required an update to the application

  3. Web Applications • Internet, documents sharing; • HTML; • Browsers • Back-Forward Navigation; • Bookmarks; • Documents accessed by URL; HTTP Protocol; All documents in one place; • Many standards: CSS, DOM, SVG, PNG; no proprietary extensions => popularity, success; • Web application: application that resides on a central server and can be accessed through web browsers; HTML content is dynamically generated.

  4. Small cost; One application for all browsers; clients have already all necessary software installed; Easy to upgrade; • No rich user experience, no visual feedback, slow; Every action results in a call to the server to generate whole application; • Great improvement on cost effectiveness => most popular type of software application • No spreadsheets, messengers, etc; • Application with rich user interaction still was developed as Client/Server Applications

  5. Rich Internet Applications • Ajax • Jesse James Garrett, “Ajax: A New Approach to Web Applications” • JavaScript, XMLHttpRequest object; • Only parts of the page are updated; • AJAX = Asynchronous JavaScript and XML.

  6. Asynchronous • Synchronous interaction model = user waits for data to be send an page to load. • In asynchronous model – the Ajax engine running on a separate thread delegates requests to server and handles the results, while the user can interact with the application • No page refresh;

  7. JavaScript • Interpreted, weakly typed programming language; • Created BrendanEich at Netscape; • Originally named Mocha, then LiveScript;renamed in 1995 to JavaScript. • No relation with Java; • Microsoft dialect: JScript; • 1996 – JavaScript submitted to standardization, resulted ECMAScript specification with JavaScript as one of its implementations;

  8. Ajax is only a name, not an acronym • Ajax can be implemented in ActionScript(Flex) • Other technologies different from XML are preferred • A proprietary protocol • JavaScript Object Notation(JSON) – lightweight data interchange format based on name/value pairs • Plain JavaScript – most powerful; JavaScript code hard to generate

  9. RIA advantages • No instalation required – software run in a browser; • Updates are automatic – when page is revisited; • Platform independent – on every platform with a browser; • More secure – little access to the local system; less likely to be harmful • More responsive – compared to classic applications • More scalable – more computations done on client • More network efficient – only necessary data is send at the server.

  10. RIA disadvantages • Requires JavaScript or specific plug-in – users can turn off javascript • No access to system resources – cannot read local files; • Hard for search engines to index fully • Depends on an Internet connection • Accessibility issues – screen readers have problems with partial updated pages;

  11. GWT • Writing JavaScript is difficult and error-prone; • JavaScript behaves a little different on different browsers; • GWT (Google Web Toolkit) • real abstraction layer that hides the detail of JavaScript; • Java to JavaScript compiler; easy to code and debug in Java; • Unit Testing; best coding practices;

  12. Features • Open-source • No plugin required (VML, Flash, Silverlight) • Dynamic and reusable UI components • Browserhistorymanagement • Support for full-featured Java debugging • GWT handles all cross-browser issues for the developer • JUnitintegration • Easyinternationalization

  13. The developers can mix handwritten JavaScript in the Java source code using the JavaScript Native Interface • Support for using Google APIs in GWT applications (Google Gears) • The developers can design and develop their application in a pure object-oriented fashion • A number of libraries are available for GWT, by Google and third parties(exGWT)

  14. GWT limitations • Not indexable by search engines • Javascript dependent • No clear separation between code and styling/layout – structure created in code;

  15. Components • Java toJavaScriptcompiler– the heart of GWT, compiles java code for client part into JavaScript • JRE Emulationlibrary– classes from Java have to have an equivalent in javascript to be used with GWT • UI building library – the biggest part; UI components; RPC support; history management; • GWT Hosted Web Browser– develop in hosted mode; code compiled in Java; used for debugging

  16. Java toJavaScriptCompiler • A program that can be started by running the class com.google.gwt.dev.GWTCompiler; • Unreferenced code is not compiled; • Doesn’t allow runtime loading of classes; • Is a little slow; • A different JavaScript code version for every browser category is generated;

  17. JRE Emulation library • Mapping of JRE into JavaScript; • Differences from JRE: • No long support; • Exception handling – no NullPointerException, OutOfMemory; no getStackTrace(); • Single threaded – JavaScript interpreters are single threaded; thread related functions and keywords have no effect • No reflection - related to the fact GWT needs to know each class and methods used in order to optimize code;

  18. JRE emulated classes • No SQL, file support(because of JavaScript security restrictions) • Only a subset of classes are emulated; • Differences in classes: • Regular expressions – different behavior; • Different serialization support from java; • Some common used classes are different • java.util.DateTimeFormat -> com.google.gwt.i18n.client.DateTimeFormat • Namespaces: java.lang; java.util; java.io;

  19. UI library

  20. Concepts • Application organized in modules; • ----------------------------------------------------------------------------------Host page – the page that has the application loader; • Running modes: • Hosted mode – code compiled in java bite code; full debugging support; running in an emulated browser; • Web mode – code compiled in JavaScript; running on real browser;

  21. Who is using GWT ? • http://www.curriki.org • http://traceurl.com • http://beta.contactoffice.com

  22. GWT 2.0 Improvements • Different terminology : “Development mode” instead of “hosted mode” • In-browser development mode – debugging in real browsers; Based on plug-ins for every browser • Code chunks – on demand loading of needed code; • Declarative user interface – UI can be declared in a XML file; • Bundling of resources – XML, CSS and text files can be combined into one file for fewer server requests;

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