Transcript Google Web Toolkit

Google Web Toolkit
Dudeanu Ermoghen
Ibănescu Diana
Melinte Laurenţiu-Ionuţ
Petrişor Ionuţ Cătălin
Evolution of applications
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1960 – Mainframes, punch cards,
monochrome text terminals;
◦ Same application, different code , one for every
operating system - big development cost;
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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
Web Applications
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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.
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• 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
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.
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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
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◦ No page refresh;
JavaScript
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Interpreted, weakly typed programming language;
Created Brendan Eich 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;
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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
RIA advantages
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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.
RIA disadvantages
Requires JavaScript or specific plugin – users can turn off javascript
 No access to system resources –
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cannot read local files;
Hard for search engines to index
fully
 Depends on an Internet connection
 Accessibility issues – screen readers have
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problems with partial updated pages;
GWT
Writing JavaScript is difficult and errorprone;
 JavaScript behaves a little different on
different browsers;
 GWT (Google Web Toolkit)
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◦ 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;
Features
Open-source
 No plugin required (VML, Flash, Silverlight)
 Dynamic and reusable UI components
 Browser history management
 Support for full-featured Java debugging
 GWT handles all cross-browser issues for
the developer
 JUnit integration
 Easy internationalization
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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)
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GWT limitations
Not indexable by search engines
 Javascript dependent
 No clear separation between code
and styling/layout – structure created
in code;
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Components
Java to JavaScript compiler – the heart
of GWT, compiles java code for client part
into JavaScript
 JRE Emulation library – 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
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Java to JavaScript Compiler
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;
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JRE Emulation library
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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;
JRE emulated classes
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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;
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Some common used classes are different
◦ java.util.DateTimeFormat ->
com.google.gwt.i18n.client.DateTimeFormat
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Namespaces: java.lang; java.util; java.io;
UI library
Concepts
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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;
Who is using GWT ?
http://www.curriki.org
 http://traceurl.com
 http://beta.contactoffice.com
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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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