finderfromdfltresource.java

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/* $Id: FinderFromDfltResource.java,v 1.5 2004/05/10 06:34:01 skitching Exp $
 *
 * 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.commons.digester.plugins.strategies;

import java.io.InputStream;
import java.util.Properties;

import org.apache.commons.digester.Digester;
import org.apache.commons.digester.plugins.RuleFinder;
import org.apache.commons.digester.plugins.RuleLoader;
import org.apache.commons.digester.plugins.PluginException;
import org.apache.commons.logging.Log;

/**
 * A rule-finding algorithm which looks for a resource file in the classpath
 * whose name is derived from the plugin class name plus a specified suffix.
 * <p>
 * If the resource-file is found, then it is expected to define a set of
 * Digester rules in xmlrules format.
 *
 * @since 1.6
 */

public class FinderFromDfltResource extends RuleFinder {
    public static String DFLT_RESOURCE_SUFFIX = "RuleInfo.xml";

    private String resourceSuffix;
    
    /** See {@link #findLoader}. */
    public FinderFromDfltResource() { 
        this(DFLT_RESOURCE_SUFFIX);
    }

    /**
     * Create a rule-finder which can load an xmlrules file, cache
     * the rules away, and later add them as a plugin's custom rules
     * when that plugin is referenced.
     *
     * @param resourceSuffix must be non-null.
     */
    public FinderFromDfltResource(String resourceSuffix) { 
        this.resourceSuffix = resourceSuffix;
    }
    
    /**
     * If there exists a resource file whose name is equal to the plugin
     * class name + the suffix specified in the constructor, then
     * load that file, run it through the xmlrules module and return an object 
     * encapsulating those rules.
     * <p>
     * If there is no such resource file, then just return null.
     * <p>
     * The returned object (when non-null) will add the selected rules to
     * the digester whenever its addRules method is invoked.
     */
    public RuleLoader findLoader(Digester d, Class pluginClass, Properties p)
                        throws PluginException {

        String resourceName = 
            pluginClass.getName().replace('.', '/') 
                    + resourceSuffix;
            
        InputStream is = 
            pluginClass.getClassLoader().getResourceAsStream(
                resourceName);

        if (is == null) {
            // ok, no such resource
            return null;
        }

        return FinderFromResource.loadRules(d, pluginClass, is, resourceName);
    }
}