Top 25 Apache Wicket Interview Questions You Must Prepare 07.Jul.2022

import org.apache.wicket.validation.CompoundValidator;

import org.apache.wicket.validation.validator.PatternValidator;

import org.apache.wicket.validation.validator.StringValidator;

 public class UsernameValidator extends CompoundValidator<String> {

  private static final long serialVersionUID = 1L;

  public UsernameValidator() {

  add(StringValidator.lengthBetween(6, 15));

add(new PatternValidator("[a-z0-9_-]+"));

  }

}

//choices in radio button

private static final List<String> TYPES = Arrays.asList(new String[] { "Shared Host", "VPN", "Dedicated Server" });

RadioChoice<String> hostingType = new RadioChoice<String>("hosting", new PropertyModel<String>(this, "selected"), TYPES);

//Java 

import org.apache.wicket.markup.html.form.DropDownChoice;

//choices in dropdown box

private static final List<String> SEARCH_ENGINES = Arrays.asList(new String[] {

"Google", "Bing", "Baidu" });

 //variable to hold the selected value from dropdown box,

//and also make "Google" is selected by default

private String selected = "Google";

 DropDownChoice<String> listSites = new DropDownChoice<String>(

"sites", new PropertyModel<String>(this, "selected"), SEARCH_ENGINES);

 //HTML for dropdown box

<select wicket:id="sites"></select>

To fix it, just override the validateOnNullValue() method like this :

FileUploadField fileUpload = new FileUploadField("fileupload",new Model<FileUpload>());

 fileUpload .add(new AbstractValidator() { 

        public boolean validateOnNullValue(){

        return true;

}

  protected void onValidate(IValidatable validatable) { 

FileUpload fileUpload = (FileUpload) validatable.getValue();

}

     protected String resourceKey() {

    return "yourErrorKey";

}

 });

Now, when no file is selected, and submit button is clicked, validation will be performed.

Yes, you can get the ServletContext class via Wicket’s WebApplication class like this :

import javax.servlet.ServletContext;

import org.apache.wicket.Page;

import org.apache.wicket.protocol.http.WebApplication;

import com.withoutbook.hello.Hello;

 public class CustomApplication extends WebApplication {

  @Override

public Class<? extends Page> getHomePage() {

  ServletContext servletContext = WebApplication.get().getServletContext();

return Hello.class; //return default page

  }

 }

final CheckBox chk0 = new CheckBox("checkbox0", Model.of(Boolean.TRUE));

 final CheckBox chk1 = new CheckBox("checkbox1",

new PropertyModel<Boolean>(this, "checkbox1"));

final CheckBox chk2 = new CheckBox("checkbox2",

new PropertyModel<Boolean>(this, "checkbox2"));

<filter-mapping>

<filter-name>wicket.wicketTest</filter-name>

<url-pattern>/*</url-pattern>

<dispatcher>REQUEST</dispatcher>

<dispatcher>ERROR</dispatcher>

</filter-mapping>

<error-page>

<error-code>404</error-code>

<location>/error404</location>

</error-page>

public class WicketApplication extends WebApplication {

  @Override

protected void init() {

  mount(new QueryStringUrlCodingStrategy("error404",ErrorPage404.class));

  }

 }

Wicket extension comes with a special “Palette” component, which render two select boxes, and allow user to move items from one select box into another.

//Java

import org.apache.wicket.extensions.markup.html.form.palette.Palette;

 final Palette<Hosting> palette = new Palette<Hosting>("palette",

new ListModel<Hosting>(selected),

new CollectionModel<Hosting>(listHosting),

renderer, 10, true);

  //HTML

<span wicket:id="palette"></span>

See summary steps to create a custom validator :

@Implements IValidator.

import org.apache.wicket.validation.IValidator;

 public class Strong PasswordValidator implements IValidator<String>{

...

}

@Override validate(IValidatable validatable).

public class StrongPasswordValidator implements IValidator<String>{

...

@Override

public void validate(IValidatable<String> validatable) {

  //get input from attached component

final String field = validatable.getValue();

  }

}

@Attached custom validator to form component.

public class CustomValidatorPage extends WebPage {

  public CustomValidatorPage(final PageParameters parameters) {

       final PasswordTextField password = new PasswordTextField("password",Model.of(""));

//attached custom validator to password field

password.add(new StrongPasswordValidator());

  //...

}

 }

//Java 

import org.apache.wicket.extensions.markup.html.form.select.Select;

import org.apache.wicket.extensions.markup.html.form.select.SelectOption;

        //variable to hold the selected value from dropdown box,

        //and also make "jQuery" selected by default

        private String selected = "jQuery";

  Select languages = new Select("languages", new PropertyModel<String>(this, "selected"));

form.add(languages);

languages.add(new SelectOption<String>("framework1", new Model<String>("Wicket")));

languages.add(new SelectOption<String>("framework2", new Model<String>("Spring MVC")));

languages.add(new SelectOption<String>("framework3", new Model<String>("JSF 2.0")));

languages.add(new SelectOption<String>("Script1", new Model<String>("jQuery")));

languages.add(new SelectOption<String>("Script2", new Model<String>("prototype")));

 //HTML for dropdown box

<select wicket:id="languages">

<optgroup label="Frameworks">

<option wicket:id="framework1" >Wicket (1.4.7)</option>

<option wicket:id="framework2" >Spring MVC (3.0)</option>

<option wicket:id="framework3" >JSF (2.0)</option>

</optgroup>

<optgroup label="JavaScript">

<option wicket:id="Script1" >jQuery (1.6.1)</option>

<option wicket:id="Script2" >prototype (1.7)</option>

</optgroup>

</select>

//create a textarea field for address

final TextArea<String> address = new TextArea<String>("address",Model.of(""));

address.setRequired(true);

A web application is a subclass of Application which associates with an instance of WicketServlet to serve pages over the HTTP protocol. This class is intended to be subclassed by framework clients to define a web application.

//Java

import org.apache.wicket.markup.html.form.upload.FileUploadField;

 form.setMultiPart(true);

form.add(fileUpload = new FileUploadField("fileUpload"));

 //HTML

<input wicket:id="fileUpload" type="file"/>

A Model holds a value for a component to display and/or edit :

  • Simple Models
  • Dynamic Models
  • Property Models
  • Compound Property Models
  • Wrapped Object Models
  • Resource Models
  • Detachable Models
  • Chaining models

create a password field

final PasswordTextField password = new PasswordTextField("password", Model.of(""));

//for properties file

password.setLabel(Model.of("Password")); 

  • Wicket is one of the most recent in a long line of Java web development frameworks.Wicket is a component-basedframework, which puts it in stark contrast to some of the earlier solutions to the sometimes monotonous task of web programming.Wicket builds on top of Sun's servlet API. Wicket is mostly removed from the request/response nature that is inherent with the web and Servlets. Instead of building controllers that must service many users and threads simultaneously, taking in requests, returning responses, and never storing any state, the Wicket developer thinks in terms of stateful components. Instead of creating a controller or action class, he or she creates a page, places components on it, and defines how each component reacts to user input.
  • It is a lightweight component-based web application framework for the Java programming.

There are 2 ways to Create New Wicket Page.

  • create a Page Extending "WebPage" Class.
  • create a Page Extending  "BasePage" ( BasePage Should Extend "WebPage").
  • IF you are using first Way you should Create Whole page with thier Header,Footer and other parts
  • and that HTML file's content may be large (complicated).This is an Unreliable way to create Page. suppose you have to change some content in Header part then you have to edit all pages that having Header Content 
  • If you are using second way, first Create your BasePage then you can extend these page to other while creating new page. in that page you have to add only Body part (Content that you want to show on that Page) Using <wicket:child />

Base class for HTML pages: Webpage Class.

Override Wicket application init() method with this “addComponentInstantiationListener(new SpringComponentInjector(this));“.

File : Wicket application class

package com.withoutbook;

 import org.apache.wicket.protocol.http.WebApplication;

import org.apache.wicket.spring.injection.annot.SpringComponentInjector;

import com.withoutbook.user.SimplePage;

 public class WicketApplication extends WebApplication {

  @Override

public Class<SimplePage> getHomePage() {

  return SimplePage.class; // return default page

}

  @Override

protected void init() {

  super.init();

addComponentInstantiationListener(new SpringComponentInjector(this));

  }

 }

Now, you can inject Spring bean into Wicket component via @SpringBean.

final TextField username = new TextField("username",Model.of(""));

username.setRequired(true);

username.add(new Username  Validator());

Form<?> form = new Form<Void>("userForm") {

  @Override

protected void onSubmit() {

  final String usernameValue = username.getModelObject();

  PageParameters pageParameters = new PageParameters();

pageParameters.add("username", usernameValue);

setResponsePage(SuccessPage.class, pageParameters);

  }

 };

// single list choice

private static final List<String> FRUITS = Arrays.asList(new String[] { "Apple", "Orange", "Banana" });

ListChoice<String> listFruits = new ListChoice<String>("fruit", new PropertyModel<String>(this, "selectedFruit"), FRUITS);

 listFruits.setMaxRows(5);

//choices in list box

private static final List<String> NUMBERS = Arrays.asList(new String[] {"Number 1", "Number 2", "Number 3", "Number 4", "Number 5", "Number 6" });

//variable to hold the selected multiple values from listbox, 

//and make "Number 6" selected as default value

private ArrayList<String> selectedNumber = new ArrayList<String>(

Arrays.asList(new String[] { "Number 6" }));

 ListMultipleChoice<String> listNumbers = new ListMultipleChoice<String>(

"number", new Model(selectedNumber), NUMBERS);

 //HTML for multiple select listbox

<select wicket:id="number"></select>

private static final List<String> LANGUAGES = Arrays.asList(new String[] {"Java", ".NET", "PHP", "Python", "C/C++" });

// hold the checkbox values

private ArrayList<String> languagesSelect = new ArrayList<String>();

final CheckBoxMultipleChoice<String> listLanguages = new CheckBoxMultipleChoice<String>("languages", new Model(languagesSelect), LANGUAGES);

<dependency>

<groupid>org.apache.wicket</groupid>

<artifactid>wicket</artifactid>

<version>1.4.17</version>

</dependency>

Wicket need SLF4J !

You have to include the slf4j logging implementation, otherwise Wicket will be failed to start.

Wicket need resource filter

Remember to add the resource filter, Wicket puts all files in same package folder, if you didn’t define the resource filter to include everything “<include>*</include>” , “html”, “properties” or other resources files may failed to copy to the correct target folder.