non-releases/trunk_before_flattening/src/java/org/apache/cocoon/acting/ResourceExistsAction.java

/*
 * Copyright 1999-2004 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.cocoon.acting;

import org.apache.avalon.framework.parameters.Parameters;
import org.apache.avalon.framework.thread.ThreadSafe;
import org.apache.cocoon.environment.Redirector;
import org.apache.cocoon.environment.SourceResolver;
import org.apache.excalibur.source.Source;
import org.apache.excalibur.source.SourceNotFoundException;

import java.util.Map;

/**
 * This action simply checks to see if a resource identified by the <code>src</code>
 * sitemap attribute exists or not. The action returns empty <code>Map</code> if
 * resource exists, <code>null</code> otherwise.
 * 
 * <p>Instead of src attribute, source can be specified using
 * parameter named <code>url</code> (this is old syntax, should be removed soon).
 * 
 * <p><b>NOTE:</b> {@link org.apache.cocoon.selection.ResourceExistsSelector}
 * should be preferred to this component, as the semantics of a Selector better
 * matches the supplied functionality.
 *
 * @version $Id$
 */
public class ResourceExistsAction extends ServiceableAction implements ThreadSafe {

    public Map act(Redirector redirector, SourceResolver resolver, Map objectModel, String src, Parameters parameters) throws Exception {
        String resourceURI = parameters.getParameter("url", src);
        Source source = null;
        try {
            source = resolver.resolveURI(resourceURI);
            if (source.exists()) {
                return EMPTY_MAP;
            }
        } catch (SourceNotFoundException e) {
            // Do not log
        } catch (Exception e) {
            getLogger().warn("Exception resolving resource " + resourceURI, e);
        } finally {
            if (source != null) {
                resolver.release(source);
            }
        }
        return null;
    }
}