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Intro to GWT

Intro to GWT. By Henry Chan hchan@apache.org. Brain Teaser to start the evening…. There are 100 houses numbered 1 to 100. During Halloween, House#1 gives 1 candy, House#2 gives 2 candies, etc up to House#100 which gives 100candies.

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Intro to GWT

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  1. Intro to GWT By Henry Chan hchan@apache.org

  2. Brain Teaser to start the evening… There are 100 houses numbered 1 to 100. During Halloween, House#1 gives 1 candy, House#2 gives 2 candies, etc up to House#100 which gives 100candies. Jack goes trick-or-treating to these houses and gets candy from each house except for one (House#X) because they gave him a “Trick” instead. Question: How do you calculate X in O(1) complexity?

  3. What is GWT? • Is it a JEE framework or is it a just a toolkit?!? • The heart of GWT is its Java -> Javascript compiler • GWT –RPC - Java->Javascript->Java … if you ever used DWR … this is way kewler • UI Library (your vanilla HTML Widgets, Layout Managers – feels like Spring) • Plugin/Development environment

  4. Current Release • Current stable release is 1.7.1 • However 2.0 milestone2 is out • Best feature of 2.0 is OOPHM (Out of Process Hosted Mode)

  5. Hello World • A TextBox and a Send button (UI objects – aka widgets, components) • Sends a message (GWT-RPC) to the server • Sent with a onClick Event - handlers • Written with an Eclipse • Entry Point: public void onModuleLoad() { • Config file … .gwt.xml • Default output directory … “war”

  6. No Javascript? • A moment of truth … there’s theory and then there’s practice … Javascript can’t die • Events are handled on the components, but every so often, you’ll still need Javascript for something whether it be integration or for some hackery reason. • Welcome JSNI (Javascript Native Interface)

  7. Embedding GWT or a whole page as a GWT Module… • Basically RootPanel.get(stringID) or RootPanel.get() • If you plan on mixing GWT with some HTML code, use RootPanel.get(stringID) otherwise your whole page will be a GWT App • An good example of an embedded GWT Module could be Google Maps

  8. Compiled code • 6 permutations – 6 browsers • Can specify generated code to be obfuscated or not • Yeah – compilation can take a long time. Reduce the permutations via the .gwt.xml file • Or run in development mode with the GWT Hosted Browser…

  9. Running in Development Mode (previously known as hosted mode) • Simple in concept … • You don’t need to wait those 15-30s to wait for your code to compile (from Java to Javascript). You make a change (reload your browser in some cases) and can even put breakpoints • Can work with Firefox, IE too – OOPHM (GWT version 2.0)

  10. GWT RPC • Like DWR, but you work with Java to Java on both ends. Done via an AJAX POST • Send a Data Transfer Object (DTO) across to/from the client to server • All DTOs must implement IsSerializable • xxxService.java • xxxServiceAsync.java • xxxServiceImpl.java

  11. Handling Exceptions • Simple … Server throws an Exception • Client catches it and acts accordingly

  12. GWT Frameworks • GWT-Ext / Gxt • SmartGWT • Vaadin

  13. GWT-Ext / Gxt • GWT-Ext is LGPL written by SanjivJivan • Unfortunately GWT-Ext will have no further major releases • GWT-Ext (aka GXT) is GPL or Commerical licences are available • Basically LGPL is better than GPL if you are using it to build a webapp for a customer who doesn’t want their Business Rules to be open source

  14. Smart GWT • The successor to GWT-Ext. • Also written by SanjivJivan • Like GWT-Ext, it is also LGPL • … except for the EE version of it which is of course commercial <sigh/> • Commercial version comes with widget->data binding

  15. DTO (Data Transfer Object) • Loosely coupled design pattern • How much power do u give the framework? • JSF has managed bean/backing beans • Wicket binds component on the server • GWT ... Is it a framework? Uses RPC to send the DTO. Biggest difference is that there’s no real binding of UI transfer objects to RemoteServiceImpl. Populating of the DTO is done on the front-end in GWT. • Flexible or just more work and maintenance? Hmmm…

  16. If u like DTOs… • Check out Dozer • Its like BeanUtils.copyProperties(destObj, origObj) except on steroids. • Note GWT does not support BigDecimal • Probably other ways to use hibernate with GWT (i.e. Gilead), but the question is: To DTO or not to DTO? When does the DTO look identical to the Domain Objects? Do we need DAOs if we are *only* talking to a RDMS (no filesystem, LDAP, Web Service, JMS involved)? • To DTO or not to DTO?

  17. Vaadin • Finnish for “I insist” • Released publically on May 2009 • Feels like Swing (from front-end to DB) • The only free GWT framework with widget databinding (HbnContainer)

  18. Comparisions • Biased … but at least a benchmark • http://vaadin.com/comparison • GWT vs JSF – well, its programming XML + Javascriptvs programming in Java. In JSF, say when a “I will send a cheque” radio button is checked, you have to disable all Credit card fields using Javascript (or go to the server and run render) • GWT vs Wicket. Wicket is a nice MVC model. Again Javascript integration with Wicket is messy. Also (not to bash Wicket), but their components aren’t that “Rich”. Its just vanilla HTML. • GWT vs Struts2. Did I say compare? Struts2 dojo plugin has been deprecated. Yikes (that’s pretty major). Struts2 can work in parallel to GWT (RootPanel.get(id) vsRootPanel.get()). You can even use FreeMarker/Velocity with GWT • Same can be said about SpringMVC • Among all the Java frameworks, the Showcase for GWT frameworks are the most complete. Forget the friggin code snippets here and there. Their showcases run right off of your IDE. • You can put break-points here, change some code and can also can view source from your IDE or from your Browser

  19. Questions and Answers Answer • The answer is 42

  20. Answer to Brain Teaser There are 100 houses numbered 1 to 100. During Halloween, House#1 gives 1 candy, House#2 gives 2 candies, etc up to House#100 which gives 100candies. Jack goes trick-or-treating to these houses and gets candy from each house except for one (House#X) because they gave him a “Trick” instead. Question: How do you calculate X in O(1) complexity? Answer: To find the house that Jack missed out on, take the summation of 1 to 100 and subtract the number of candies Jack collected. i.e. if Jack collected 5008 candies across those 99 houses, the house number he missed was 42 (the summation of 1 to 100 is 5050 and subtracting 5008 would give 42)

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