fr.putnami.pwt.core.widget.client.DocumentMeta.java Source code

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Here is the source code for fr.putnami.pwt.core.widget.client.DocumentMeta.java

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/**
 * This file is part of pwt.
 *
 * pwt is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser
 * General Public License as published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * pwt is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the
 * implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
 * General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License along with pwt. If not,
 * see <http://www.gnu.org/licenses/>.
 */
package fr.putnami.pwt.core.widget.client;

import com.google.common.base.Strings;
import com.google.gwt.dom.client.Document;
import com.google.gwt.dom.client.Element;
import com.google.gwt.dom.client.HeadElement;
import com.google.gwt.dom.client.MetaElement;
import com.google.gwt.dom.client.NodeList;
import com.google.gwt.dom.client.SpanElement;
import com.google.gwt.event.logical.shared.AttachEvent;
import com.google.gwt.uibinder.client.UiConstructor;
import com.google.gwt.user.client.ui.IsWidget;

import fr.putnami.pwt.core.widget.client.base.AbstractWidget;

/**
 * The DocumentMeta is a widget that alter a meta tag in the document head section
 * <p>
 * This widget changes or creates the first meta tag with the matching name when this widget is
 * loaded. When the widget unload event is fired, the tag is reverted to the original state.
 * </p>
 *
 */
public class DocumentMeta extends AbstractWidget {

    /**
     * The PageAttachHandler handles the attach event and alter the meta tag.
     */
    private class PageAttachHandler implements AttachEvent.Handler {
        private String fromContent;

        /*
         * (non-Javadoc)
         *
         * @see
         * com.google.gwt.event.logical.shared.AttachEvent.Handler#onAttachOrDetach(com.google.gwt.event
         * .logical.shared.AttachEvent)
         */
        @Override
        public void onAttachOrDetach(AttachEvent event) {
            if (event.isAttached()) {
                if (content != null) {
                    MetaElement metaTag = DocumentMeta.getDescriptionTag(name, true);
                    fromContent = Strings.emptyToNull(metaTag.getContent());
                    metaTag.setContent(content);
                }
            } else {
                MetaElement metaTag = DocumentMeta.getDescriptionTag(name, true);
                if (fromContent != null) {
                    metaTag.setContent(fromContent);
                } else {
                    metaTag.removeFromParent();
                }
            }
        }
    }

    private final String name;
    private String content;

    /**
     * Instantiates a new document meta tag.
     *
     * @param name the name attribute
     */
    @UiConstructor
    public DocumentMeta(String name) {
        super(SpanElement.TAG);
        assert name != null : "attribute name must not be null";
        this.name = name;
        endContruct();
    }

    /**
     * constructor by copy.
     *
     * @param source the source to copy
     */
    protected DocumentMeta(DocumentMeta source) {
        super(source);
        this.name = source.name;
        this.content = source.content;
        endContruct();
    }

    /**
     * End the construction of the widget.
     */
    private void endContruct() {
        addAttachHandler(new PageAttachHandler());
    }

    /*
     * (non-Javadoc)
     *
     * @see fr.putnami.pwt.core.editor.client.factory.CloneableWidget#cloneWidget()
     */
    @Override
    public IsWidget cloneWidget() {
        return new DocumentMeta(this);
    }

    /**
     * Gets the name attribute.
     *
     * @return the name
     */
    public String getName() {
        return name;
    }

    /**
     * Gets the content attribute.
     *
     * @return the content attribute
     */
    public String getContent() {
        return content;
    }

    /**
     * Sets the meta content attribute.
     *
     * @param content the new content attribute of the meta tag
     */
    public void setContent(String content) {
        this.content = content;
    }

    /**
     * Return the first meta tag from the head section with name matching. <br>
     * If createIfMissing the tag is created and added at the end of the head section.<br>
     * <p>
     * <strong>Note : </strong> the name is case insensitive
     * </p>
     *
     * @param name the name attribute of the metta tag
     * @param createIfMissing create the tag in the head section if missing
     * @return meta tag element or null
     */
    public static MetaElement getDescriptionTag(String name, boolean createIfMissing) {
        Document doc = Document.get();
        HeadElement head = doc.getHead();
        assert head != null : "No head section found in the document";
        assert name != null : "the name must not be null";

        NodeList<Element> tags = head.getElementsByTagName("meta");
        MetaElement metaTag = null;
        for (int i = 0; i < tags.getLength(); i++) {
            metaTag = (MetaElement) tags.getItem(i);
            if (name.equalsIgnoreCase(metaTag.getName())) {
                return metaTag;
            }
        }
        if (createIfMissing) {
            metaTag = doc.createMetaElement();
            metaTag.setName(name);
            head.appendChild(metaTag);
        }
        return metaTag;
    }

}