1. Apache Wicket: web applications with just Java
Xavier Hanin
JavaZone ‘07

2. Independent Java Consultant Customers
Who is Xavier Hanin
Independent Java Consultant
Customers
Open Source
Renault

3. Agenda
What is Wicket
Core concepts of Wicket
Developing a custom component
Q&A

4. Wicket in a Nutshell Open Source (Apache Software Foundation)
Component based
Pure Java + Pure HTML
Simple
Enthusiastic community

5. 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

6. 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

7. 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

8. Component versus ‘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

9. Excellent localization and style support
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

10. Features Integration Fancy components 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

11. Features State management clustering support back button support
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

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

13. Agenda
What is Wicket
Core concepts of Wicket
Developing a custom component
Q&A

14. Wicket’s concepts
Application
Session
RequestCycle
Components
Behaviors
Models

15. 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 …

16. Configured in web.xml: Application <filter>
<filter-name>wicket</servlet-name>
<filter-class>
org.apache.wicket.protocol.http.WicketFilter
</filter-class>
<init-param>
<param-name>applicationClassName</param-name>
<param-value>example.MyApplication</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</filter>

17. Wicket’s concepts
Application
Session
RequestCycle
Components
Behaviors
Models

18. 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

19. 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);

20. Wicket’s concepts
Application
Session
RequestCycle
Components
Behaviors
Models

21. 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

22. RequestCycle Two types of requests: Stateful Stateless
Tied to specific user session
Not bookmarkable
Stateless
Not necessarily tied to specific user session
Bookmarkable

23. Wicket’s concepts
Application
Session
RequestCycle
Components
Behaviors
Models

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

25. 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

26. Components and markup
A component is identified in markup with wicket:id
Html: <h1 wicket:id=“msg”>Gets replaced</h1>
Java: new Label(“msg”, “Hello, World!”);
Final (wicket tags can be stripped):
<h1>Hello, World!</h1>

27. Component can have its own markup file
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

28. A page: Hello, World!

29. Wicket’s concepts
Application
Session
RequestCycle
Components
Behaviors
Models

30. 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); }
});
Output: <tr class=“odd”>…</tr> <tr class=“even”>…</tr>

31. Behaviors Change attributes of your component’s markup
Add javascript events
Add Ajax behavior
component.add( new AjaxSelfUpdatingBehavior( Duration.seconds(1)));

32. Wicket’s concepts
Application
Session
RequestCycle
Components
Behaviors
Models

33. <<Person>>
Models
Models bind your POJO’s to Wicket components
Label(“name”, model)
<<Person>>
+name : String
+city : String
PropertyModel

34. Lazy binding in Java sucks
Models
Lazy binding in Java sucks
Doesn’t update:
new TextField(“txt”, person.getName())
Gives null pointers:
new Label(“street”, person.getAddress().getStreet())
Solution: OGNL/EL like expressions

35. Be aware for nulls when using updates:
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”));

36. Agenda
What is Wicket
Core concepts of Wicket
Developing a custom component
Q&A

37. 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. »

38. Custom components for all
464 pages
20 minutes

39. Example: Password strength
weak
medium
strong

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

41. 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

42. Example: Password strength

43. Example: Password strength

44. Example: Password strength

45. 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

46. Smart component oriented web framework
Conclusion
Smart component oriented web framework
Easy creation and use of custom components
Enthustiatic community
Join in!

47. Agenda
What is Wicket
Core concepts of Wicket
Developing a custom component
Q&A