Commons Digester example source code file (FromXmlRuleSet.java)

This example Commons Digester source code file (FromXmlRuleSet.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

digester, digester, digesterruleparser, digesterruleparser, fromxmlruleset, fromxmlruleset, inputsourcexmlrulesloader, net, network, override, sax, string, url, urlxmlrulesloader, xmlloadexception, xmlloadexception, xmlrulesloader

The Commons Digester FromXmlRuleSet.java source code

/* $Id: FromXmlRuleSet.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.xmlrules;


import java.net.URL;

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

import org.xml.sax.InputSource;

/**
 * A Digester rule set where the rules come from an XML file.
 *
 * @since 1.2
 */
public class FromXmlRuleSet extends RuleSetBase {

    public static final String DIGESTER_DTD_PATH = "org/apache/commons/digester/xmlrules/digester-rules.dtd";

    /**
     * The file containing the Digester rules, in XML.
     */
    private XMLRulesLoader rulesLoader;

    /**
     * The rule set for parsing the Digester rules
     */
    private DigesterRuleParser parser;

    /**
        * The digester for loading the rules xml.
        */
    private Digester rulesDigester;

    /**
     * Constructs a FromXmlRuleSet using the default DigesterRuleParser and
     * rulesDigester.
     * @param rulesXml the path to the XML document defining the Digester rules
     */
    public FromXmlRuleSet(URL rulesXml) {
        this(rulesXml, new DigesterRuleParser(), new Digester());
    }

    /**
     * Constructs a FromXmlRuleSet using the default DigesterRuleParser and
     * a ruleDigester for loading the rules xml.
     * @param rulesXml the path to the XML document defining the Digester rules
     * @param rulesDigester the digester to read the rules xml.
     */
    public FromXmlRuleSet(URL rulesXml, Digester rulesDigester) {
        this(rulesXml, new DigesterRuleParser(), rulesDigester);
    }

    /**
     * @param rulesXml the path to the XML document defining the Digester rules
     * @param parser an instance of DigesterRuleParser, for parsing the rules from XML
     */
    public FromXmlRuleSet(URL rulesXml, DigesterRuleParser parser) {
        this(rulesXml, parser, new Digester());
    }

    /**
     * @param rulesXml the path to the XML document defining the Digester rules
     * @param parser an instance of DigesterRuleParser, for parsing the rules from XML
     * @param rulesDigester the digester used to load the Xml rules.
     */
    public FromXmlRuleSet(URL rulesXml, DigesterRuleParser parser, Digester rulesDigester) {
        init(new URLXMLRulesLoader(rulesXml), parser, rulesDigester);
    }

    /**
     * Constructs a FromXmlRuleSet using the default DigesterRuleParser and
     * rulesDigester.
     * @param inputSource load the xml rules from this InputSource
     */
    public FromXmlRuleSet(InputSource inputSource) {
        this(inputSource, new DigesterRuleParser(), new Digester());
    }
    
    /**
     * Constructs a FromXmlRuleSet using the default DigesterRuleParser and
     * a ruleDigester for loading the rules xml.
     * @param inputSource load the xml rules from this InputSource
     * @param rulesDigester the digester to read the rules xml.
     */
    public FromXmlRuleSet(InputSource inputSource, Digester rulesDigester) {
        this(inputSource, new DigesterRuleParser(), rulesDigester);
    }

    /**
     * @param inputSource load the xml rules from this InputSource
     * @param parser an instance of DigesterRuleParser, for parsing the rules from XML
     */
    public FromXmlRuleSet(InputSource inputSource, DigesterRuleParser parser) {
        this(inputSource, parser, new Digester());
    }

    /**
     * @param inputSource load the xml rules from this InputSource
     * @param parser an instance of DigesterRuleParser, for parsing the rules from XML
     * @param rulesDigester the digester used to load the Xml rules.
     */
    public FromXmlRuleSet(InputSource inputSource, DigesterRuleParser parser, Digester rulesDigester) {
        init(new InputSourceXMLRulesLoader(inputSource), parser, rulesDigester);
    }
    
    /**
     * Base constructor
     */
    private void init(XMLRulesLoader rulesLoader, DigesterRuleParser parser, Digester rulesDigester) {
        this.rulesLoader = rulesLoader;
        this.parser = parser;
        this.rulesDigester = rulesDigester;
    }
    
    /**
     * Adds to the digester the set of Rule instances defined in the
     * XML file for this rule set.
     * @see org.apache.commons.digester.RuleSetBase
     */
    @Override
    public void addRuleInstances(org.apache.commons.digester.Digester digester) throws XmlLoadException {
        addRuleInstances(digester, null);
    }
    
    /**
     * Adds to the digester the set of Rule instances defined in the
     * XML file for this rule set.
     * <p>
     * Note that this method doesn't have a matching one on the DigesterLoader
     * class, because it is not expected to be widely used, and DigesterLoader's
     * load method is already heavily overloaded.
     *
     * @param digester is the digester that rules will be added to.
     * @param basePath is a path that will be prefixed to every
     * pattern string defined in the xmlrules input file.
     *
     * @see org.apache.commons.digester.RuleSetBase
     * @since 1.6
     */
    public void addRuleInstances(
    org.apache.commons.digester.Digester digester,
    String basePath) 
    throws XmlLoadException {
        
        URL dtdURL = getClass().getClassLoader().getResource(DIGESTER_DTD_PATH);
        if (dtdURL == null) {
            throw new XmlLoadException("Cannot find resource \"" +
                    DIGESTER_DTD_PATH + "\"");
        }
        parser.setDigesterRulesDTD(dtdURL.toString());
        parser.setTarget(digester);
        parser.setBasePath(basePath);

        rulesDigester.addRuleSet(parser);
        rulesDigester.push(parser);

        rulesLoader.loadRules();
    }
    
    /** 
     * Worker class encapsulates loading mechanisms.
     * Private until some reason is found to make it public.
     */
    private abstract static class XMLRulesLoader {
        /** Load rules now */
        public abstract void loadRules()  throws XmlLoadException;
    }
    
    /** Loads XMLRules from an URL */
    private class URLXMLRulesLoader extends XMLRulesLoader {
        private URL url;
        public URLXMLRulesLoader(URL url) {
            this.url = url;
        }
        
        @Override
        public void loadRules() throws XmlLoadException {
            try {
                rulesDigester.parse(url.openStream());
            } catch (Exception ex) {
                throw new XmlLoadException(ex);
            }
        }
    }

    /** Loads XMLRules from an InputSource */
    private class InputSourceXMLRulesLoader extends XMLRulesLoader {
        private InputSource inputSource;
        public InputSourceXMLRulesLoader(InputSource inputSource) {
            this.inputSource = inputSource;
        }
        
        @Override
        public void loadRules() throws XmlLoadException {
            try {
                rulesDigester.parse(inputSource);
            } catch (Exception ex) {
                throw new XmlLoadException(ex);
            }
        }
    }
}