/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.wicket.markup.head;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import org.apache.wicket.request.Response;
import org.apache.wicket.util.io.IClusterable;
/**
* {@code HeaderItem} represents anything that can be rendered into the header. This can, for
* example, be a {@linkplain JavaScriptHeaderItem script} or a {@linkplain CssHeaderItem stylesheet}
* , but also {@linkplain OnEventHeaderItem event triggers} or {@linkplain StringHeaderItem free
* form text}. {@code HeaderItem}s are used by {@link org.apache.wicket.markup.head.ResourceAggregator} to be able to collect all
* header sections in a uniform way. All {@code HeaderItem}s are expected to have decent
* {@code equals}, {@code hashCode} and {@code toString} (for debugging).
*
* @author papegaaij
*/
public abstract class HeaderItem implements IClusterable
{
/**
* @return The dependencies this {@code HeaderItem} has. Dependencies will always be rendered
* before the item itself.
*/
public List<HeaderItem> getDependencies()
{
return new ArrayList<>();
}
/**
* @return The resources this {@code HeaderItem} provides. As these resources are provided by
* this item, they will no longer be rendered.
*/
public Iterable<? extends HeaderItem> getProvidedResources()
{
return Collections.emptyList();
}
/**
* @return The tokens this {@code HeaderItem} can be identified by. If any of the tokens has
* already been rendered, this {@code HeaderItem} will not be rendered.
*/
public abstract Iterable<?> getRenderTokens();
/**
* Renders the {@code HeaderItem} to the response.
*
* @param response
*/
public abstract void render(Response response);
}