Glossary | Apache Wicket

The definitions use plain words first and the Wicket class second. “Similar to” names the closest idea in other frameworks; the comparison is never exact.

Ajax request target: The list of components to redraw in response to an Ajax request, plus any JavaScript to run. Ajax callbacks such as onClick(AjaxRequestTarget) receive one; AjaxRequestTarget.add() puts a component in it.; Similar to: the render attribute of JSF’s <f:ajax>, or out-of-band swaps (hx-swap-oob) in htmx.
Application: The object that represents your web application, one per deployment. You subclass WebApplication to name the home page and configure everything else in init().; Similar to: a Spring Boot application class with its configuration, or faces-config.xml in JSF.
Behavior: An add-on you attach to a component to change its tag, contribute CSS or JavaScript, or react to browser events, without subclassing the component. Behaviors extend Behavior; Ajax behaviors extend AbstractAjaxBehavior.; Similar to: attribute directives in Angular, custom directives in Vue.
Border: A component that wraps markup around its children: the border provides the frame, and <wicket:body> marks where the children go.; Similar to: a React component that renders its children inside a frame, or a layout decorator in Thymeleaf.
Component: A Java object that renders one part of a page and handles the events for it, such as a label, a link or a text field. It is tied to a tag in the markup through wicket:id. All components extend Component.; Similar to: a JSF UIComponent, a Vaadin component, or a React or Vue component rendered on the server.
Component tree: The hierarchy of components that make up a page. Containers (MarkupContainer), such as pages, panels and forms, hold child components, and the hierarchy matches the nesting of the wicket:id tags in the markup.; Similar to: the JSF component tree, or a DOM that lives on the server.
CompoundPropertyModel: A model for a container whose children use their own wicket:id as the name of the property they read and write on the model’s object.; Similar to: Spring MVC form binding with th:field, which binds inputs to bean properties by name.
Converter: An object that turns submitted text into a Java value and a value back into text, for numbers, dates and the other types it knows. Converters implement IConverter; you register your own on the ConverterLocator.; Similar to: a JSF Converter, or a Spring Formatter.
Deployment mode, development mode: The two runtime configuration types of an application. Development mode adds checks, reloads changed markup and shows stack traces; deployment mode leaves those out for speed and safety. See Switch between development and deployment mode.; Similar to: the Development and Production project stages of JSF, or Spring profiles.
Detach: The cleanup step at the end of every request, in which components and models drop data they can load again, before Wicket stores the page.; Similar to: releasing request-scoped beans at the end of a request.
Detachable model: A model that loads its object when it is first asked for it in a request, and forgets it when the request ends, so the stored page keeps only what it needs to load it again, such as an id. LoadableDetachableModel is the usual base class.; Similar to: loading an entity by id in every Spring MVC request instead of keeping it in the session.
Enclosure: A <wicket:enclosure> tag around markup that is shown only when a chosen child component is visible, so its label and surrounding tags disappear with it.; Similar to: th:if in Thymeleaf or v-if in Vue on a wrapping element.
Feedback message, FeedbackPanel: A message for the user, such as a validation error or a confirmation, with a level: error, warning, info, success. Components record them with error(), info() and similar methods, and a FeedbackPanel shows them.; Similar to: <h:messages> in JSF, or flash messages in Spring MVC.
Form: A component for an HTML <form> that runs the submit: it converts and validates the input of its form components, updates their models, and calls onSubmit() or onError().; Similar to: <h:form> in JSF, or a Spring MVC form with its @PostMapping handler.
Form component: A component that takes user input, such as TextField, CheckBox or DropDownChoice. Form components extend FormComponent.; Similar to: JSF input components such as <h:inputText>.
Fragment: A piece of markup defined inside the markup file of a page or panel with <wicket:fragment>, and shown by a Fragment component, so small variations need no file of their own.; Similar to: a th:fragment defined in the same Thymeleaf template, or a named template block.
Header item: A reference to CSS, JavaScript or other content for the <head> of a page, which a component contributes in renderHead(). Wicket includes each item once, in dependency order. HeaderItem is the base class.; Similar to: <h:outputScript> in JSF.
LambdaModel: A model built from a getter and a setter, often two method references such as Person::getName and Person::setName. The compiler checks it, unlike a property expression in a string.; Similar to: a computed property with a getter and setter in Vue.
Markup: The HTML file of a page, panel or border, kept next to its Java class. It is plain HTML with wicket:id attributes and a few wicket: tags.; Similar to: a Thymeleaf template or a JSF Facelets file, without an expression language.
Markup id: The id attribute Wicket writes on a component’s tag when you call setOutputMarkupId(true). Ajax needs it to find the tag to replace.; Similar to: the generated client id of a JSF component.
Markup inheritance: A page or panel subclass inherits the markup of its parent class. The parent marks one place with <wicket:child/>, and the subclass fills it with the content of its <wicket:extend> tag.; Similar to: template inheritance with the Thymeleaf Layout Dialect, or a Facelets template with <ui:composition>.
Model: The object a component asks for the value it shows, and hands a new value to when the user submits one. Models implement IModel, which has getObject() and setObject(). Because IModel has only one abstract method, a lambda is a read-only model.; Similar to: a property in JavaFX, or a computed property with a getter and setter in Vue.
Mount: Giving a page or resource a fixed, readable URL path in init(), for example mountPage("/products/${id}", ProductPage.class).; Similar to: @GetMapping("/products/{id}") in Spring MVC.
Package resource: A file, such as CSS, JavaScript or an image, stored in a Java package next to the component that uses it, and served by Wicket with a URL that changes when the file does.; Similar to: a resource library in META-INF/resources in JSF.
Page: A component that is a complete HTML document, with its own markup file. Every rendered HTML page in a Wicket application is an instance of a Page subclass, usually WebPage.; Similar to: a JSF view, or a Spring MVC controller method together with its template.
Page parameters: The named and indexed values in the URL of a bookmarkable page, which the page receives as PageParameters in its constructor.; Similar to: @PathVariable and @RequestParam in Spring MVC, or view parameters in JSF.
Page store: Where Wicket keeps the stateful pages of each session between requests: the most recent ones in memory, and serialized pages on disk.; Similar to: server-side view state in JSF.
Panel: A reusable component with its own markup file, inside a <wicket:panel> tag. Panels are the usual way to build your own components.; Similar to: a JSF composite component, or a React or Vue component with its own template.
Repeater: A component that renders its markup once for each item in a collection: RepeatingView, ListView, DataView and others.; Similar to: th:each in Thymeleaf, v-for in Vue, or <ui:repeat> in JSF.
Request cycle: The processing of one request, from mapping the URL to a handler to writing the response and detaching. RequestCycle.get() returns the current one.; Similar to: the JSF lifecycle, or what Spring’s DispatcherServlet does for one request.
Request mapper: An object that translates a URL into a request handler and the other way around, used for mounted pages and resources. Mappers implement IRequestMapper.; Similar to: handler mappings in Spring MVC.
Resource: Anything Wicket serves that is not a page: a stylesheet, an image, a download, a generated PDF or a JSON response. Resources implement IResource.; Similar to: a Spring MVC handler that returns a ResponseEntity with bytes, or a static resource handler.
Resource reference: A named, serializable pointer to a resource, which Wicket turns into a URL and resolves when the URL is requested.; Similar to: a JSF resource identified by library and name.
Session: The Wicket object for one visitor, kept in the HTTP session once something needs to be remembered: the locale, the signed-in user, feedback messages, and the visitor’s stateful pages. You can subclass WebSession for typed fields.; Similar to: a session-scoped bean in Spring or CDI.
Stateful page, stateless page: A stateful page is stored after it renders, so later requests, such as link clicks and form submits, go to the same page object. A stateless page is created anew for every request and needs no session. Wicket makes a page stateful as soon as one of its components needs that.; Similar to: JSF views with view state versus transient views; every Spring MVC page is stateless.
Validator: An object that checks the converted input of a form component and records an error when it fails, such as StringValidator or EmailAddressValidator. Validators implement IValidator.; Similar to: a JSF Validator, or a Spring Validator.
WicketTester: A test helper that runs your application in memory, so a JUnit test can render pages, click links, submit forms and check the result without a browser or server.; Similar to: Spring’s MockMvc.
wicket:id: The attribute that ties a tag in the markup to the component with the same id in Java. Each component added in Java needs a tag with its id, at the same place in the hierarchy.; Similar to: the id that binds a Facelets tag to a JSF component, or a th: attribute in Thymeleaf, but without an expression.