001 // Copyright 2004, 2005 The Apache Software Foundation
002 //
003 // Licensed under the Apache License, Version 2.0 (the "License");
004 // you may not use this file except in compliance with the License.
005 // You may obtain a copy of the License at
006 //
007 // http://www.apache.org/licenses/LICENSE-2.0
008 //
009 // Unless required by applicable law or agreed to in writing, software
010 // distributed under the License is distributed on an "AS IS" BASIS,
011 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012 // See the License for the specific language governing permissions and
013 // limitations under the License.
014
015 package org.apache.tapestry.contrib.link;
016
017 import org.apache.hivemind.ApplicationRuntimeException;
018 import org.apache.tapestry.IMarkupWriter;
019 import org.apache.tapestry.IRequestCycle;
020 import org.apache.tapestry.Tapestry;
021 import org.apache.tapestry.components.ILinkComponent;
022 import org.apache.tapestry.engine.ILink;
023 import org.apache.tapestry.html.Body;
024 import org.apache.tapestry.link.DefaultLinkRenderer;
025 import org.apache.tapestry.link.ILinkRenderer;
026
027 /**
028 * A link renderer that ensures that the generated link uses POST instead of GET request and
029 * is therefore no longer limited in size.
030 * <p>
031 * Theoretically, browsers should support very long URLs,
032 * but in practice they often start behaving strangely if the URLs are more than 256 characters.
033 * This renderer uses JavaScript to generate forms containing the requested link parameters and
034 * then "post" them when the link is selected.
035 * As a result, the data is sent to the server using a POST request with a very short URL
036 * and there is no longer a limitation in the size of the parameters.
037 * <p>
038 * In short, simply add the following parameter to your <code>DirectLink</code>,
039 * <code>ExternalLink</code>, or other such link components:
040 * <pre>
041 * renderer="ognl: @org.apache.tapestry.contrib.link.FormLinkRenderer@RENDERER"
042 * </pre>
043 * and they will automatically start using POST rather than GET requests. Their parameters
044 * will no longer be limited in size.
045 *
046 * @author mb
047 * @since 4.0
048 */
049 public class FormLinkRenderer extends DefaultLinkRenderer
050 {
051 /**
052 * A public singleton instance of the <code>FormLinkRenderer</code>.
053 * <p>
054 * Since the <code>FormLinkRenderer</code> is stateless, this instance
055 * can serve all links within your application without interference.
056 */
057 public final static ILinkRenderer RENDERER = new FormLinkRenderer();
058
059 public void renderLink(IMarkupWriter writer, IRequestCycle cycle, ILinkComponent linkComponent) {
060 IMarkupWriter wrappedWriter = null;
061
062 if (cycle.getAttribute(Tapestry.LINK_COMPONENT_ATTRIBUTE_NAME) != null)
063 throw new ApplicationRuntimeException(
064 Tapestry.getMessage("AbstractLinkComponent.no-nesting"),
065 linkComponent,
066 null,
067 null);
068
069 cycle.setAttribute(Tapestry.LINK_COMPONENT_ATTRIBUTE_NAME, linkComponent);
070
071 String actionId = cycle.getNextActionId();
072 String formName = "LinkForm" + actionId;
073
074 boolean hasBody = getHasBody();
075
076 boolean disabled = linkComponent.isDisabled();
077
078 if (!disabled && !cycle.isRewinding())
079 {
080 ILink l = linkComponent.getLink(cycle);
081 String anchor = linkComponent.getAnchor();
082
083 Body body = Body.get(cycle);
084
085 if (body == null)
086 throw new ApplicationRuntimeException(
087 Tapestry.format("must-be-contained-by-body", "FormLinkRenderer"),
088 this,
089 null,
090 null);
091
092 String function = generateFormFunction(formName, l, anchor);
093 body.addBodyScript(function);
094
095 if (hasBody)
096 writer.begin(getElement());
097 else
098 writer.beginEmpty(getElement());
099
100 writer.attribute(getUrlAttribute(), "javascript: document." + formName + ".submit();");
101
102 beforeBodyRender(writer, cycle, linkComponent);
103
104 // Allow the wrapped components a chance to render.
105 // Along the way, they may interact with this component
106 // and cause the name variable to get set.
107
108 wrappedWriter = writer.getNestedWriter();
109 }
110 else
111 wrappedWriter = writer;
112
113 if (hasBody)
114 linkComponent.renderBody(wrappedWriter, cycle);
115
116 if (!disabled && !cycle.isRewinding())
117 {
118 afterBodyRender(writer, cycle, linkComponent);
119
120 linkComponent.renderAdditionalAttributes(writer, cycle);
121
122 if (hasBody)
123 {
124 wrappedWriter.close();
125
126 // Close the <element> tag
127
128 writer.end();
129 }
130 else
131 writer.closeTag();
132 }
133
134 cycle.removeAttribute(Tapestry.LINK_COMPONENT_ATTRIBUTE_NAME);
135
136 }
137
138 private String generateFormFunction(String formName, ILink link, String anchor)
139 {
140 String[] parameterNames = link.getParameterNames();
141
142 StringBuffer buf = new StringBuffer();
143 buf.append("function prepare" + formName + "() {\n");
144
145 buf.append(" var html = \"\";\n");
146 buf.append(" html += \"<div style='position: absolute'>\";\n");
147
148 String url = link.getURL(anchor, false);
149 buf.append(" html += \"<form name='" + formName + "' method='post' action='" + url + "'>\";\n");
150
151 for (int i = 0; i < parameterNames.length; i++) {
152 String parameter = parameterNames[i];
153 String[] values = link.getParameterValues(parameter);
154 for (int j = 0; j < values.length; j++) {
155 String value = values[j];
156 buf.append(" html += \"<input type='hidden' name='" + parameter + "' value='" + value + "'/>\";\n");
157 }
158 }
159 buf.append(" html += \"<\" + \"/form>\";\n");
160 buf.append(" html += \"<\" + \"/div>\";\n");
161 buf.append(" document.write(html);\n");
162 buf.append("}\n");
163
164 buf.append("prepare" + formName + "();\n\n");
165
166 return buf.toString();
167 }
168
169 }