Commons Digester example source code file (PluginDeclarationRule.java)

This example Commons Digester source code file (PluginDeclarationRule.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Commons Digester tags/keywords

declaration, error, override, plugindeclarationrule, plugininvalidinputexception, plugininvalidinputexception, pluginmanager, pluginrules, pluginrules, properties, properties, rule, string, string, util

The Commons Digester PluginDeclarationRule.java source code

/* $Id: PluginDeclarationRule.java 992060 2010-09-02 19:09:47Z simonetripodi $
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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;

import java.util.Properties;

import org.apache.commons.digester.Digester;
import org.apache.commons.digester.Rule;

/**
 * A Digester rule which allows the user to pre-declare a class which is to
 * be referenced later at a plugin point by a PluginCreateRule.
 * <p>
 * Normally, a PluginDeclarationRule is added to a Digester instance with
 * the pattern "{root}/plugin" or "* /plugin" where {root} is the name of 
 * the root tag in the input document.
 *
 * @since 1.6
 */

public class PluginDeclarationRule extends Rule {

    //------------------- constructors ---------------------------------------

    /** constructor  */
    public PluginDeclarationRule() {
        super();
    }

    //------------------- methods --------------------------------------------

    /**
     * Invoked upon reading a tag defining a plugin declaration. The tag
     * must have the following mandatory attributes:
     * <ul>
     *   <li> id 
     *   <li> class 
     * </ul>
     *
     *@param namespace The xml namespace in which the xml element which
     * triggered this rule resides.
     *@param name The name of the xml element which triggered this rule.
     *@param attributes The set of attributes on the xml element which
     * triggered this rule.
     *@exception java.lang.Exception
     */

    @Override
    public void begin(String namespace, String name,
                      org.xml.sax.Attributes attributes)
                      throws java.lang.Exception {
                 
        int nAttrs = attributes.getLength();
        Properties props = new Properties();
        for(int i=0; i<nAttrs; ++i) {
            String key = attributes.getLocalName(i);
            if ((key == null) || (key.length() == 0)) {
                key = attributes.getQName(i);
            }
            String value = attributes.getValue(i);
            props.setProperty(key, value);
        }
        
        try {
            declarePlugin(digester, props);
        } catch(PluginInvalidInputException ex) {
            throw new PluginInvalidInputException(
                "Error on element [" + digester.getMatch() + 
                "]: " + ex.getMessage());
        }
    }
    
    public static void declarePlugin(Digester digester, Properties props)
    throws PluginException {
        
        String id = props.getProperty("id");
        String pluginClassName = props.getProperty("class");
        
        if (id == null) {
            throw new PluginInvalidInputException(
                "mandatory attribute id not present on plugin declaration");
        }

        if (pluginClassName == null) {
            throw new PluginInvalidInputException(
                "mandatory attribute class not present on plugin declaration");
        }

        Declaration newDecl = new Declaration(pluginClassName);
        newDecl.setId(id);
        newDecl.setProperties(props);

        PluginRules rc = (PluginRules) digester.getRules();
        PluginManager pm = rc.getPluginManager();

        newDecl.init(digester, pm);
        pm.addDeclaration(newDecl);
        
        // Note that it is perfectly safe to redeclare a plugin, because
        // the declaration doesn't add any rules to digester; all it does
        // is create a RuleLoader instance whch is *capable* of adding the
        // rules to the digester.
    }
}