Source Code Cross Referenced for ResourceExistsSelector.java in  » Content-Management-System » apache-lenya-2.0 » org » apache » cocoon » selection » Java Source Code / Java DocumentationJava Source Code and Java Documentation

001:        /*
002:         * Licensed to the Apache Software Foundation (ASF) under one or more
003:         * contributor license agreements.  See the NOTICE file distributed with
004:         * this work for additional information regarding copyright ownership.
005:         * The ASF licenses this file to You under the Apache License, Version 2.0
006:         * (the "License"); you may not use this file except in compliance with
007:         * the License.  You may obtain a copy of the License at
008:         * 
009:         *      http://www.apache.org/licenses/LICENSE-2.0
010:         * 
011:         * Unless required by applicable law or agreed to in writing, software
012:         * distributed under the License is distributed on an "AS IS" BASIS,
013:         * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014:         * See the License for the specific language governing permissions and
015:         * limitations under the License.
016:         */
017:        package org.apache.cocoon.selection;
018:
019:        import java.util.Map;
020:
021:        import org.apache.avalon.framework.activity.Disposable;
022:        import org.apache.avalon.framework.logger.AbstractLogEnabled;
023:        import org.apache.avalon.framework.parameters.Parameters;
024:        import org.apache.avalon.framework.service.ServiceException;
025:        import org.apache.avalon.framework.service.ServiceManager;
026:        import org.apache.avalon.framework.service.Serviceable;
027:        import org.apache.avalon.framework.thread.ThreadSafe;
028:        import org.apache.excalibur.source.Source;
029:        import org.apache.excalibur.source.SourceNotFoundException;
030:        import org.apache.excalibur.source.SourceResolver;
031:
032:        /**
033:         * Selects the first of a set of Resources (usually files) that exists.
034:         * 
035:         * <p>
036:         * A parameter 'prefix', 
037:         * <pre>
038:         *   &lt;map:parameter src="prefix" value="<code>some/path</code>"/&lt;
039:         * </pre>
040:         * may be supplied to the selector instance.  This prefix is prepended to all
041:         * test expressions before evaluation.  The default prefix is '' (empty string),
042:         * meaning that all expressions are relative to the current sitemap, unless
043:         * explicitly overridden.
044:         * 
045:         * <p><b>NOTE:</b>
046:         * Provided resource URI is resolved as Source, relative to the current
047:         * sitemap, which differs from behavior of selector in previous versions.
048:         * To resolve resource paths relative to the context root, provide prefix
049:         * parameter:
050:         * <pre>
051:         *   &lt;map:parameter name="prefix" value="context://"/&lt;
052:         * </pre>
053:         * 
054:         * <p>
055:         * For example, we could define a ResourceExistsSelector with:
056:         * <pre>
057:         * &lt;map:selector name="resource-exists"
058:         *               logger="sitemap.selector.resource-exists"
059:         *               src="org.apache.cocoon.selection.ResourceExistsSelector" /&lt;
060:         * </pre>
061:         * And use it to build a PDF from XSL:FO or a higher-level XML format with:
062:         *
063:         * <pre>
064:         *  &lt;map:match pattern="**.pdf"&lt;
065:         *    &lt;map:select type="resource-exists"&lt;
066:         *       &lt;map:when test="context/xdocs/{1}.fo"&lt;
067:         *          &lt;map:generate src="content/xdocs/{1}.fo" /&lt;
068:         *       &lt;/map:when&lt;
069:         *       &lt;map:otherwise&lt;
070:         *         &lt;map:generate src="content/xdocs/{1}.xml" /&lt;
071:         *         &lt;map:transform src="stylesheets/document2fo.xsl" /&lt;
072:         *       &lt;/map:otherwise&lt;
073:         *    &lt;/map:select&lt;
074:         *    &lt;map:serialize type="fo2pdf" /&lt;
075:         * </pre>
076:         *
077:         * @author <a href="mailto:jefft@apache.org">Jeff Turner</a>
078:         * @author <a href="mailto:vgritsenko@apache.org">Vadim Gritsenko</a>
079:         * @version CVS $Id: ResourceExistsSelector.java 433543 2006-08-22 06:22:54Z crossley $
080:         */
081:        public class ResourceExistsSelector extends AbstractLogEnabled
082:                implements  ThreadSafe, Serviceable, Disposable, Selector {
083:
084:            private ServiceManager manager;
085:            private SourceResolver resolver;
086:
087:            public void service(ServiceManager manager) throws ServiceException {
088:                this .manager = manager;
089:                this .resolver = (SourceResolver) manager
090:                        .lookup(SourceResolver.ROLE);
091:            }
092:
093:            public void dispose() {
094:                this .manager.release(this .resolver);
095:                this .resolver = null;
096:                this .manager = null;
097:            }
098:
099:            public boolean select(String expression, Map objectModel,
100:                    Parameters parameters) {
101:                String resourceURI = parameters.getParameter("prefix", "")
102:                        + expression;
103:                Source source = null;
104:                try {
105:                    source = resolver.resolveURI(resourceURI);
106:                    return source.exists();
107:                } catch (SourceNotFoundException e) {
108:                    return false;
109:                } catch (Exception e) {
110:                    getLogger().warn(
111:                            "Exception resolving resource " + resourceURI, e);
112:                    return false;
113:                } finally {
114:                    if (source != null) {
115:                        resolver.release(source);
116:                    }
117:                }
118:            }
119:        }