org.xchain.framework.digester.RuleSetRegistryConfigurator.java Source code

Introduction

Here is the source code for org.xchain.framework.digester.RuleSetRegistryConfigurator.java

Source

/**
 *    Copyright 2011 meltmedia
 *
 *    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.xchain.framework.digester;

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

import java.net.URL;
import java.util.Enumeration;
import java.io.IOException;

import org.xml.sax.Attributes;
import org.xml.sax.InputSource;

import org.xchain.framework.net.UrlSourceUtil;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * @author Christian Trimble
 * @author Devon Tackett
 * @author Jason Rose
 * @author Josh Kennedy
 */
public class RuleSetRegistryConfigurator {
    public static Logger log = LoggerFactory.getLogger(RuleSetRegistryConfigurator.class);

    public static String RULE_SET_REGISTRATION_RESOURCE = "org/xchain/digester/rule-set-registry.xml";
    public static String RULE_SET_REGISTRATION_NAMESPACE_URI = "http://xchain.org/rule-set-registry/1.0";

    public void configure() throws Exception {
        // get all of the config files for the registry.
        Enumeration<URL> registrationUrlEnumeration = getConfigurationUrlEnumeration(
                RULE_SET_REGISTRATION_RESOURCE);

        // for each registration document, register the configured rule sets.
        while (registrationUrlEnumeration.hasMoreElements()) {
            URL registrationUrl = registrationUrlEnumeration.nextElement();

            if (log.isDebugEnabled()) {
                log.debug("Loading registration file for url '" + registrationUrl.toExternalForm() + "'.");
            }

            // process the registrations defined in this registration url.
            processRegistrationUrl(registrationUrl);

            if (log.isDebugEnabled()) {
                log.debug("Done loading registration file for url '" + registrationUrl.toExternalForm() + "'.");
            }
        }
    }

    public Enumeration<URL> getConfigurationUrlEnumeration(String resourceName) throws IOException {
        // get the enumeration of all the matching resources.
        return Thread.currentThread().getContextClassLoader().getResources(resourceName);
    }

    public void processRegistrationUrl(URL registrationUrl) throws Exception {
        // create a digester to parse the registration url.
        Digester digester = new Digester();
        digester.addRuleSet(new RegistrationRuleSet());

        // create a source for the url.
        InputSource registrationUrlSource = UrlSourceUtil.createSaxInputSource(registrationUrl);

        // parse the registration url.
        digester.parse(registrationUrlSource);
    }

    public static class RegistrationRuleSet extends RuleSetBase {
        public static String REGISTRY_ELEMENT = "registry";
        public static String RULE_SET_ELEMENT = "rule-set";

        public static String CLASS_NAME_ATTRIBUTE = "class-name";

        public RegistrationRuleSet() {
            this.namespaceURI = RULE_SET_REGISTRATION_NAMESPACE_URI;
        }

        public void addRuleInstances(Digester digester) {
            digester.setNamespaceAware(true);
            digester.setRuleNamespaceURI(getNamespaceURI());

            digester.addRule(REGISTRY_ELEMENT, new LoadRuleSetRegistryRule());

            String ruleSetPath = REGISTRY_ELEMENT + "/" + RULE_SET_ELEMENT;
            digester.addRule(ruleSetPath, new RegisterRuleSetRule());
        }

        public static class LoadRuleSetRegistryRule extends Rule {
            public void begin(String namespace, String name, Attributes attributes) throws Exception {
                RuleSetRegistry registry = RuleSetRegistry.getInstance();

                // push the registry on the top of the stack.
                digester.push(registry);
            }
        }

        public static class RegisterRuleSetRule extends Rule {
            public void begin(String namespace, String name, Attributes attributes) throws Exception {
                String className = getValue(attributes, "", CLASS_NAME_ATTRIBUTE);

                if (className == null) {
                    throw new Exception("The class name is a required attribute for rule-set tags.");
                }

                // create an instance of the class specified for the rule set.
                Object object = Thread.currentThread().getContextClassLoader().loadClass(className).newInstance();

                // verify that the class is an instance of RuleSet.
                if (!(object instanceof RuleSet)) {
                    throw new Exception(
                            "The class-name attribute of rule-set must specify a subclass of org.apache.commons.digester.RuleSet.");
                }

                // cast the created class to a rule set.
                RuleSet ruleSet = (RuleSet) object;

                // get the rule set registry from the digester.
                RuleSetRegistry registry = (RuleSetRegistry) digester.peek();

                // add the rule set to the registry.
                registry.addRuleSet(ruleSet);

            }
        }
    }

    public static String getValue(Attributes attributes, String namespace, String name) {
        String value = null;

        int index = attributes.getIndex(namespace, name);

        if (index >= 0) {
            value = attributes.getValue(index);
        }

        return value;
    }
}