// Copyright 2004, 2005 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.contrib.link;
import org.apache.hivemind.ApplicationRuntimeException;
import org.apache.tapestry.IMarkupWriter;
import org.apache.tapestry.IRequestCycle;
import org.apache.tapestry.Tapestry;
import org.apache.tapestry.TapestryUtils;
import org.apache.tapestry.components.ILinkComponent;
import org.apache.tapestry.engine.ILink;
import org.apache.tapestry.html.Body;
import org.apache.tapestry.link.DefaultLinkRenderer;
import org.apache.tapestry.link.ILinkRenderer;
/**
* A link renderer that ensures that the generated link uses POST instead of GET
* request and is therefore no longer limited in size.
* <p>
* Theoretically, browsers should support very long URLs, but in practice they
* often start behaving strangely if the URLs are more than 256 characters. This
* renderer uses JavaScript to generate forms containing the requested link
* parameters and then "post" them when the link is selected. As a result, the
* data is sent to the server using a POST request with a very short URL and
* there is no longer a limitation in the size of the parameters.
* <p>
* In short, simply add the following parameter to your <code>DirectLink</code>,
* <code>ExternalLink</code>, or other such link components:
*
* <pre>
* renderer = "ognl: @org.apache.tapestry.contrib.link.FormLinkRenderer@RENDERER"
* </pre>
*
* and they will automatically start using POST rather than GET requests. Their
* parameters will no longer be limited in size.
* @author mb
* @since 4.0
*/
public class FormLinkRenderer extends DefaultLinkRenderer
{
/**
* A public singleton instance of the <code>FormLinkRenderer</code>.
* <p>
* Since the <code>FormLinkRenderer</code> is stateless, this instance can
* serve all links within your application without interference.
*/
public static final ILinkRenderer RENDERER = new FormLinkRenderer();
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);
String formName = cycle.getUniqueId("LinkForm");
boolean hasBody = getHasBody();
boolean disabled = linkComponent.isDisabled();
if (!disabled && !cycle.isRewinding())
{
ILink l = linkComponent.getLink(cycle);
String anchor = linkComponent.getAnchor();
Body body = (Body) TapestryUtils.getPageRenderSupport(cycle, linkComponent);
String function = generateFormFunction(formName, l, anchor);
body.addBodyScript(linkComponent, function);
if (hasBody)
writer.begin(getElement());
else writer.beginEmpty(getElement());
writer.attribute(getUrlAttribute(), "javascript: document."
+ formName + ".submit();");
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 && !cycle.isRewinding())
{
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);
}
private String generateFormFunction(String formName, ILink link,
String anchor)
{
String[] parameterNames = link.getParameterNames();
StringBuffer buf = new StringBuffer();
buf.append("function prepare" + formName + "() {\n");
buf.append(" var html = \"\";\n");
buf.append(" html += \"<div style='position: absolute'>\";\n");
String url = link.getURL(anchor, false);
buf.append(" html += \"<form name='" + formName
+ "' method='post' action='" + url + "'>\";\n");
for(int i = 0; i < parameterNames.length; i++)
{
String parameter = parameterNames[i];
String[] values = link.getParameterValues(parameter);
if (values != null) {
for (int j = 0; j < values.length; j++) {
String value = values[j];
buf.append(" html += \"<input type='hidden' name='" + parameter + "' value='" + value + "'/>\";\n");
}
}
}
buf.append(" html += \"<\" + \"/form>\";\n");
buf.append(" html += \"<\" + \"/div>\";\n");
buf.append(" document.write(html);\n");
buf.append("}\n");
buf.append("prepare" + formName + "();\n\n");
return buf.toString();
}
}