findersetproperties.java

JAVA 文章管理系统源码

/* $Id: FinderSetProperties.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 java.io.InputStream;
import java.io.FileInputStream;
import java.io.IOException;

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 expects the user to specify whether
 * "automatic property setting" is desired. If this class discovers that
 * this is in fact the case for a declaration, then a RuleLoader is returned
 * which, when invoked, adds a single SetPropertiesRule instance to the
 * digester.
 * <p>
 * This allows ordinary JavaBean classes to be used as plugins, and have
 * xml attributes be mapped to bean properties of the same name, without
 * any custom plugin rules being created for them.
 * <p>
 * This RuleFinder is typically used as the <i>last</i> RuleFinder, so that
 * automatic property setting only occurs if there is no other source of
 * custom rules available.
 *
 * @since 1.6
 */

public class FinderSetProperties extends RuleFinder {
    public static String DFLT_PROPS_ATTR = "setprops";
    public static String DFLT_FALSEVAL = "false";

    private String propsAttr;
    private String falseval;
    
    /** See {@link #findLoader}. */
    public FinderSetProperties() {
        this(DFLT_PROPS_ATTR, DFLT_FALSEVAL);
    }
    
    /**
     * Create a rule-finder which will arrange for a SetPropertiesRule to
     * be defined for each instance of a plugin, so that xml attributes
     * map to bean properties.
     * <p>
     * Param falseval will commonly be the string "false" for config files 
     * written in English.
     *
     * @param propsAttr must be non-null.
     * @param falseval must be non-null.
     */
    public FinderSetProperties(String propsAttr, String falseval) { 
        this.propsAttr = propsAttr;
        this.falseval = falseval;
    }
    
    /**
     * Returns a RuleLoader <i>unless</i> the properties contain an entry
     * with the name matching constructor param propsAttr, and the value 
     * matching what is in falseval.
     * <p>
     * If no custom source of rules for a plugin is found, then the user
     * almost always wants xml attributes to map to java bean properties,
     * so this is the default behaviour unless the user explicitly indicates
     * that they do <i>not</i> want a SetPropertiesRule to be provided for
     * the plugged-in class.
     * <p>
     * The returned object (when non-null) will add a SetPropertiesRule to
     * the digester whenever its addRules method is invoked.
     */
    public RuleLoader findLoader(Digester d, Class pluginClass, Properties p) {
        String state = p.getProperty(propsAttr);
        if ((state != null)  && state.equals(falseval)) {
            // user has explicitly disabled automatic setting of properties.
            // this is not expected to be common, but allowed.
            return null;
        }
        
        return new LoaderSetProperties();
    }
}