Share a resource across the application

Register a shared resource when one resource instance should serve the whole application under a fixed key, and components that link to it should not need a reference to the instance. If you want a readable URL instead, mount it: Give a resource a URL.

Register the resource

Add the resource to the shared resources in init(), under a name:

WicketApplication.java

@Override
protected void init() {
    super.init();
    getSharedResources().add("ordersCsv", new OrdersCsvResource());
}

OrdersCsvResource is the resource from Generate a resource in code.

Refer to it by name

Anywhere in the application, a SharedResourceReference with the same name finds the registered resource:

add(new ResourceLink<Void>("export", new SharedResourceReference("ordersCsv")));

The link renders a URL with the scope and the name:

./wicket/resource/org.apache.wicket.Application/ordersCsv

The scope of resources added by name alone is Application. A name that is not registered gives a 404 response when the URL is requested, so register shared resources before the first request, in init().

To get the URL as text, use RequestCycle.get().urlFor(new SharedResourceReference("ordersCsv"), null).

Scope a shared resource to a class

Pass a class to keep names apart, for example in a library that registers resources from an IInitializer:

getSharedResources().add(ReportsModule.class, "summary", null, null, null, new SummaryResource());

new SharedResourceReference(ReportsModule.class, "summary")

The three null arguments are the locale, style and variation, which are part of the key. Configure a module with an initializer shows where a library runs such code.

Keep the resource safe for concurrent use

There is one instance for all users and all requests, and requests run in parallel. Do not keep request or user data in fields of the resource; read what you need from the request, the session or a service while it responds.

Package resources are shared resources too, without registration: Wicket finds them by their class and file name. Register only resources that you create in code.