finderfromdfltclass.java

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/* $Id: FinderFromDfltClass.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.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;

/**
 * A rule-finding algorithm which looks for a method with a specific name
 * on a class whose name is derived from the plugin class name.
 *
 * @since 1.6
 */

public class FinderFromDfltClass extends RuleFinder {
    public static String DFLT_RULECLASS_SUFFIX = "RuleInfo";
    public static String DFLT_METHOD_NAME = "addRules";
    
    private String rulesClassSuffix;
    private String methodName;
    
    /** See {@link #findLoader}. */
    public FinderFromDfltClass() {
        this(DFLT_RULECLASS_SUFFIX, DFLT_METHOD_NAME);
    }
    
    /**
     * Create a rule-finder which invokes a method on a class whenever 
     * dynamic rules for a plugin need to be loaded. See the findRules 
     * method for more info.
     *
     * @param rulesClassSuffix must be non-null.
     * @param methodName may be null.
     */
     public FinderFromDfltClass(String rulesClassSuffix, String methodName) { 
        this.rulesClassSuffix = rulesClassSuffix;
        this.methodName = methodName;
    }
    
    /**
     * If there exists a class whose name is the plugin class name + the
     * suffix specified to the constructor, then load that class, locate 
     * the appropriate rules-adding method on that class, and return an 
     * object encapsulating that info.
     * <p>
     * If there is no such class, then just return null.
     * <p>
     * The returned object (when non-null) will invoke the target method
     * on the selected class whenever its addRules method is invoked. The
     * target method is expected to have the following prototype:
     * <code> public static void xxxxx(Digester d, String patternPrefix); </code>
     */
    public RuleLoader findLoader(Digester digester, Class pluginClass, Properties p)
                            throws PluginException {

        String rulesClassName = pluginClass.getName() + rulesClassSuffix;

        Class rulesClass = null;
        try {
            rulesClass = digester.getClassLoader().loadClass(rulesClassName);
        } catch(ClassNotFoundException cnfe) {
            // ok, ignore
        }

        if (rulesClass == null) {
            // nope, no rule-info class in the classpath
            return null;
        }
        
        if (methodName == null) {
            methodName = DFLT_METHOD_NAME;
        }
        
        return new LoaderFromClass(rulesClass, methodName);
    }
}