tapestry-framework/src/org/apache/tapestry/link/DefaultLinkRenderer.java

//  Copyright 2004 The Apache Software Foundation
//
// Licensed 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.tapestry.link;

import org.apache.tapestry.ApplicationRuntimeException;
import org.apache.tapestry.IMarkupWriter;
import org.apache.tapestry.IRequestCycle;
import org.apache.tapestry.Tapestry;
import org.apache.tapestry.components.ILinkComponent;
import org.apache.tapestry.engine.ILink;

/**
 *  Default implementation of {@link org.apache.tapestry.link.ILinkRenderer}, which
 *  does nothing special.  Can be used as a base class to provide
 *  additional handling.
 *
 *  @author Howard Lewis Ship, David Solis
 *  @version $Id$
 *  @since 3.0
 **/

public class DefaultLinkRenderer implements ILinkRenderer
{
    /**
     *  A shared instance used as a default for any link that doesn't explicitly
     *  override.
     * 
     **/

    public static final ILinkRenderer SHARED_INSTANCE = new DefaultLinkRenderer();

    public void renderLink(IMarkupWriter writer, IRequestCycle cycle, ILinkComponent linkComponent)
    {
        IMarkupWriter wrappedWriter = null;

        if (cycle.getAttribute(Tapestry.LINK_COMPONENT_ATTRIBUTE_NAME) != null)
            throw new ApplicationRuntimeException(
                Tapestry.getMessage("AbstractLinkComponent.no-nesting"),
                linkComponent,
                null,
                null);

        cycle.setAttribute(Tapestry.LINK_COMPONENT_ATTRIBUTE_NAME, linkComponent);

        boolean hasBody = getHasBody();

        boolean disabled = linkComponent.isDisabled();

        if (!disabled)
        {
            ILink l = linkComponent.getLink(cycle);

            if (hasBody)
                writer.begin(getElement());
            else
                writer.beginEmpty(getElement());

            writer.attribute(getUrlAttribute(), constructURL(l, linkComponent.getAnchor(), cycle));

            beforeBodyRender(writer, cycle, linkComponent);

            // Allow the wrapped components a chance to render.
            // Along the way, they may interact with this component
            // and cause the name variable to get set.

            wrappedWriter = writer.getNestedWriter();
        }
        else
            wrappedWriter = writer;

        if (hasBody)
            linkComponent.renderBody(wrappedWriter, cycle);

        if (!disabled)
        {
            afterBodyRender(writer, cycle, linkComponent);

            linkComponent.renderAdditionalAttributes(writer, cycle);

            if (hasBody)
            {
                wrappedWriter.close();

                // Close the <element> tag

                writer.end();
            }
            else
                writer.closeTag();
        }

        cycle.removeAttribute(Tapestry.LINK_COMPONENT_ATTRIBUTE_NAME);
    }

    /**
     *  Converts the EngineServiceLink into a URI or URL.  This implementation
     *  simply invokes {@link ILink#getURL(String, boolean)}.
     * 
     **/

    protected String constructURL(ILink link, String anchor, IRequestCycle cycle)
    {
        return link.getURL(anchor, true);
    }

    /**
     *  Invoked after the href attribute has been written but before
     *  the body of the link is rendered (but only if the link
     *  is not disabled).
     * 
     *  <p>
     *  This implementation does nothing.
     * 
     **/

    protected void beforeBodyRender(IMarkupWriter writer, IRequestCycle cycle, ILinkComponent link)
    {
    }

    /**
     *  Invoked after the body of the link is rendered, but before
     *  {@link ILinkComponent#renderAdditionalAttributes(IMarkupWriter, IRequestCycle)} is invoked
     *  (but only if the link is not disabled).
     * 
     *  <p>
     *  This implementation does nothing.
     * 
     **/

    protected void afterBodyRender(IMarkupWriter writer, IRequestCycle cycle, ILinkComponent link)
    {
    }

    /** @since 3.0 **/

    protected String getElement()
    {
        return "a";
    }

    protected String getUrlAttribute()
    {
        return "href";
    }

    protected boolean getHasBody()
    {
        return true;
    }
}