Apache Wicket: web applications with just Java

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Apache Wicket web applications with just Java

• Xavier Hanin
• JavaZone 07

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Who is Xavier Hanin

• Independent Java Consultant
• Customers
• Open Source

Renault
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Agenda

• What is Wicket
• Core concepts of Wicket
• Developing a custom component
• QA

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Wicket in a Nutshell

• Open Source (Apache Software Foundation)
• Component based
• Pure Java Pure HTML
• Simple
• Enthusiastic community

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What is Wicket?

• The technology enabling component-oriented,
  programmatic manipulation of markup
• The mission bringing object oriented programming
  to the web application view layer
• The reward have a fun job and be good friends
  with your manager again

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Achieving these goals through

• Keeping simple things simple
• Utilizing an object-oriented component model
  where components are truly self contained
• Re-applying the Model View Controller pattern on
  components instead of requests, with models as
  first class citizens
• Having a clean separation of concerns between
  HTML and Java

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Achieving these goals through

• Providing transparent, fully automated state
  management
• Keeping configuration needs to the minimum
• No more XML!
• Making using creating custom components easier
  than any framework out there

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Component versus traditional

• Traditional
• Struts, WebWork, Spring MVC, etc.
• Proven for web
• A lot of web developers available
• Components
• JSF, Wicket, Tapestry, etc.
• Traditional model for UI development on thick
  clients
• A lot of developers available

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Features

• Page composition
• panels, borders and markup inheritance
• Excellent localization and style support
• template and resource loading (_be.html, .xml)
• localized models (e.g. for labels)
• sophisticated resource bundle lookup (composition
  inheritance hierarchy)
• automatic client capabilities detection

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Features

• Integration
• Spring
• Guice
• Hibernate
• JasperReports
• OSGi
• Fancy components
• sortable, filterable, pageable, data aware tables
• date picker, rich text editor, Google Maps
• tabbed panel, navigation, tree, wizard

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Features

• State management
• type safe sessions
• clustering support
• back button support
• Double submit strategies
• render redirect/ redirect to buffered response/
  none
• Testing support
• JUnit testing
• extensive logging and error reporting

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Features

• Ajax support and components
• Ajax without writing JavaScript, Dojo,
  Scriptaculous, ...
• Header contribution
• Javascript CSS
• URL mounting
• pretty URLs
• Component level security

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Agenda

• What is Wicket
• Core concepts of Wicket
• Developing a custom component
• QA

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Wickets concepts

• Application
• Session
• RequestCycle
• Components
• Behaviors
• Models

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Application

• Main entry point for your web application
• Configuration
• Output Wicket specific tags?
• Watch for markup changes every ?
• Defines homepage
• Factories for
• Session
• RequestCycle
• Security

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Application

• Configured in web.xml
• ltfiltergt
• ltfilter-namegtwicketlt/servlet-namegt
• ltfilter-classgt
• org.apache.wicket.protocol.http.WicketFilt
  er
• lt/filter-classgt
• ltinit-paramgt
• ltparam-namegtapplicationClassNamelt/param-na
  megt
• ltparam-valuegtexample.MyApplicationlt/param-
  valuegt
• lt/init-paramgt
• ltload-on-startupgt1lt/load-on-startupgt
• lt/filtergt

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Wickets concepts

• Application
• Session
• RequestCycle
• Components
• Behaviors
• Models

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Session

• Abstraction of a user session
• Storage typically in HttpSession
• Stores session specific data
• Locale, Client info (browser vendor and version)
• Your own data?
• Logged in user
• Shopping cart contents
• Limited page history for back button support

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Session

• class MySession extends WebSession
• private ShoppingCart cart
• public ShoppingCart getCart()
• public void setCart(ShoppingCart cart)
• mysession.setCart(new ShoppingCart())
• ShoppingCart cart mysession.getCart()
• cart.add(quantity, selectedProduct)

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Wickets concepts

• Application
• Session
• RequestCycle
• Components
• Behaviors
• Models

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RequestCycle

• Steps in a request cycle
• Create request cycle object
• Decode the request
• Identify request target (page, component, )
• Process event (onClick, onSubmit, )
• Respond (page, component, image, pdf, )
• Clean up

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RequestCycle

• Two types of requests
• Stateful
• Tied to specific user session
• Not bookmarkable
• Stateless
• Not necessarily tied to specific user session
• Bookmarkable

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Wickets concepts

• Application
• Session
• RequestCycle
• Components
• Behaviors
• Models

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Components

• encapsulate the programmatic manipulation of
  markup
• can receive an event
• onClick, onSubmit
• know how and where to render itself

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Component

• Ultimate super class wicket.Component

• Label
• MultiLineLabel
• TextField
• PasswordTextField
• Image
• Link
• Tree
• BookmarkablePageLink
• JasperReports

• ListView
• Loop
• PagingNavigator
• ImageMap
• Button
• Ajax
• Sorting, paging repeaters
• Wizard
• DatePicker

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Components and markup

• A component is identified in markup with
  wicketid
• Html lth1 wicketidmsggtGets replacedlt/h1gt
• Javanew Label(msg, Hello, World!)
• Final (wicket tags can be stripped)
• lth1gtHello, World!lt/h1gt

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Components and markup

• Component can have its own markup file
• Page
• Panel
• Border
• Put java, markup and supporting files in same
  package on class path

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A page Hello, World!
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Wickets concepts

• Application
• Session
• RequestCycle
• Components
• Behaviors
• Models

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Behaviors

• Behaviors are plug-ins for Components
• They can modify the components markup
• item.add(new AbstractBehavior()
• public void onComponentTag(
• Component component, ComponentTag tag)
• String css (((Item)component).getIndex() 2
  0)
• ? "even" "odd"
• tag.put("class", css)
• )
• Outputlttr classoddgtlt/trgtlttr
  classevengtlt/trgt

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Behaviors

• Change attributes of your components markup
• Add javascript events
• Add Ajax behavior
• component.add( new AjaxSelfUpdatingBehavior(
  Duration.seconds(1)))

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Wickets concepts

• Application
• Session
• RequestCycle
• Components
• Behaviors
• Models

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Models

• Models bind your POJOs to Wicket components

Label(name, model)
ltltPersongtgt name String city String
PropertyModel
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Models

• Lazy binding in Java sucks
• Doesnt update
• new TextField(txt, person.getName())
• Gives null pointers
• new Label(street, person.getAddress().getStreet(
  ))
• Solution OGNL/EL like expressions

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Models

• PropertyModel
• new PropertyModel(person, name)
• new PropertyModel(person, address.street)
• Be aware for nulls when using updates
• Person p new Person()
• new TextField(street, new PropertyModel(p,
  address.street))

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Agenda

• What is Wicket
• Core concepts of Wicket
• Developing a custom component
• QA

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Why a custom component?

• Eelco Hillenius
•  Imagine being told that you can use Java as
  your programming language, but at the same time
  being told not to create your own classes. ...
• I fail to understand why that has to be
  different for UI development, and Wicket proves
  it doesn't have to be so. 

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Custom components for all
464 pages
20 minutes
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Example Password strength
weak
medium
strong
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Components

• Creating custom component is as easy as typing in
  extends
• Extends wicket.Component down the line
• Available on application classpath

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Example Password strength

• Panels provide grouping
• Have own markup file
• Can be exchanged in pages for other components
• Can contribute to header
• Can contain any number of components, including
  panels

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Example Password strength
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Example Password strength
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Example Password strength
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Components are reusable

• Put them in a JAR
• Package all necessary resources
• HTML, JavaScript, Images, CSS
• class file
• Put JAR on classpath
• Ready for (re)use

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Conclusion

• Smart component oriented web framework
• Easy creation and use of custom components
• Enthustiatic community
• Join in!
• http//wicket.apache.org/
• users_at_wicket.apache.org

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Agenda

• What is Wicket
• Core concepts of Wicket
• Developing a custom component
• QA