Apache Wicket Interview Questions and Answers

//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>

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 :

import org.apache.wicket.validation.IValidator;

 

public class StrongPasswordValidator implements IValidator<String>{

...

}

public class StrongPasswordValidator implements IValidator<String>{

...

@Override

public void validate(IValidatable<String> validatable) {

 

//get input from attached component

final String field = validatable.getValue();

 

}

}

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());

 

//...

}

 

}

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.

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

 

}

 

}

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.

<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));

 

}

 

}