org.apache.wicket.markup.head.IHeaderResponse.java Source code

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Here is the source code for org.apache.wicket.markup.head.IHeaderResponse.java

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/*
 * 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.io.Closeable;

import org.apache.wicket.request.Response;
import org.apache.wicket.request.resource.ResourceReference;

/**
 * Interface that is used to render header elements (usually javascript and CSS references).
 * 
 * Implementation of this interface is responsible for filtering duplicate contributions (so that
 * for example the same javascript is not loaded twice) during the same request.
 * 
 * @author Matej Knopp
 */
public interface IHeaderResponse extends Closeable {
    /**
     * Renders the given {@link HeaderItem} to the response if none of the
     * {@linkplain HeaderItem#getRenderTokens() tokens} of the item has been rendered before.
     * 
     * @param item
     *            The item to render.
     */
    void render(HeaderItem item);

    /**
     * Marks the given object as rendered. The object can be anything (string, resource reference,
     * etc...). The purpose of this function is to allow user to manually keep track of rendered
     * items. This can be useful for items that are expensive to generate (like interpolated text).
     * 
     * @param object
     *            object to be marked as rendered.
     */
    void markRendered(Object object);

    /**
     * Returns whether the given object has been marked as rendered.
     * <ul>
     * <li>Methods <code>renderJavaScriptReference</code> and <code>renderCSSReference</code> mark
     * the specified {@link ResourceReference} as rendered.
     * <li>Method <code>renderJavaScript</code> marks List of two elements (first is javascript body
     * CharSequence and second is id) as rendered.
     * <li>Method <code>renderString</code> marks the whole string as rendered.
     * <li>Method <code>markRendered</code> can be used to mark an arbitrary object as rendered
     * </ul>
     * 
     * @param object
     *            Object that is queried to be rendered
     * @return Whether the object has been marked as rendered during the request
     */
    boolean wasRendered(Object object);

    /**
     * Returns the response that can be used to write arbitrary text to the head section.
     * <p>
     * Note: This method is kind of dangerous as users are able to write to the output whatever they
     * like.
     * 
     * @return Response
     */
    Response getResponse();

    /**
     * Mark Header rendering is completed and subsequent usage will be ignored. If some kind of
     * buffering is used internally, this action will mark that the contents has to be flushed out.
     */
    @Override
    void close();

    /**
     * @return if header rendering is completed and subsequent usage will be ignored
     */
    boolean isClosed();
}