Commons Digester example source code file (FinderFromResource.java)

This example Commons Digester source code file (FinderFromResource.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

class, finderfromresource, finderfromresource, inputstream, io, loaderfromstream, override, pluginexception, pluginexception, properties, ruleloader, ruleloader, string, string, unable, util

The Commons Digester FinderFromResource.java source code

/* $Id: FinderFromResource.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.strategies;

import java.util.Properties;
import java.io.InputStream;

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 a resource
 * name (ie a file in the classpath). The file is expected to contain Digester
 * rules in xmlrules format.
 *
 * @since 1.6
 */

public class FinderFromResource extends RuleFinder {
    /** 
     * Name of xml attribute on the plugin declaration which is used
     * to configure rule-loading for that declaration. 
     */
    public static String DFLT_RESOURCE_ATTR = "resource";
    
    /** See {@link #findLoader}. */
    private String resourceAttr;
    
    /** Constructor. */
    public FinderFromResource() {
        this(DFLT_RESOURCE_ATTR);
    }

    /** See {@link #findLoader}. */
    public FinderFromResource(String resourceAttr) { 
        this.resourceAttr = resourceAttr;
    }
    
    /**
     * If there exists a property with the name matching constructor param
     * resourceAttr, then load that file, run it through the xmlrules
     * module and return an object encapsulating those rules.
     * <p>
     * If there is no matching property provided, then just return null.
     * <p>
     * The returned object (when non-null) will add the selected rules to
     * the digester whenever its addRules method is invoked.
     */
    @Override
    public RuleLoader findLoader(Digester d, Class<?> pluginClass, Properties p)
                        throws PluginException {

        String resourceName = p.getProperty(resourceAttr);
        if (resourceName == null) {
            // nope, user hasn't requested dynamic rules to be loaded
            // from a specific file.
            return null;
        }
        
        InputStream is = 
            pluginClass.getClassLoader().getResourceAsStream(
                resourceName);

        if (is == null) {
            throw new PluginException(
                "Resource " + resourceName + " not found.");
        }
        
         return loadRules(d, pluginClass, is, resourceName);
    }
    
    /**
     * Open the specified resource file (ie a file in the classpath, 
     * including being within a jar in the classpath), run it through
     * the xmlrules module and return an object encapsulating those rules.
     * 
     * @param d is the digester into which rules will eventually be loaded.
     * @param pluginClass is the class whose xml params the rules are parsing.
     * @param is is where the xmlrules will be read from, and must be non-null.
     * @param resourceName is a string describing the source of the xmlrules,
     *  for use in generating error messages.
     */
    public static RuleLoader loadRules(Digester d, Class<?> pluginClass, 
                        InputStream is, String resourceName)
                        throws PluginException {

        try {
            RuleLoader loader = new LoaderFromStream(is);
            return loader;
        } catch(Exception e) {
            throw new PluginException(
                "Unable to load xmlrules from resource [" + 
                resourceName + "]", e);
        } finally {
            try {
                is.close();
            } catch(java.io.IOException ioe) {
                throw new PluginException(
                    "Unable to close stream for resource [" + 
                    resourceName + "]", ioe);
            }
        }
    }
}