Commons Digester example source code file (PluginManager.java)

This example Commons Digester source code file (PluginManager.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, declaration, declaration, hashmap, hashmap, list, log, pluginexception, pluginmanager, pluginmanager, properties, ruleloader, ruleloader, string, util

The Commons Digester PluginManager.java source code

/* $Id: PluginManager.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.HashMap;
import java.util.List;
import java.util.Properties;
import java.util.Iterator;

import org.apache.commons.digester.Digester;

import org.apache.commons.logging.Log;

/**
 * Coordinates between PluginDeclarationRule and PluginCreateRule objects,
 * providing a place to share data between instances of these rules.
 * <p>
 * One instance of this class exists per PluginRules instance.
 *
 * @since 1.6
 */

public class PluginManager {

    /** Map of classname->Declaration */
    private HashMap<String, Declaration> declarationsByClass = new HashMap();

    /** Map of id->Declaration  */
    private HashMap<String, Declaration> declarationsById = new HashMap();

    /** the parent manager to which this one may delegate lookups. */
    private PluginManager parent;
    
    /** 
     * The object containing data that should only exist once for each
     * Digester instance.
     */
    private PluginContext pluginContext;
    
    //------------------- constructors ---------------------------------------
    
    /** Construct a "root" PluginManager, ie one with no parent. */
    public PluginManager(PluginContext r) {
        pluginContext = r;
    }

    /** 
     * Construct a "child" PluginManager. When declarations are added to
     * a "child", they are stored within the child and do not modify the
     * parent, so when the child goes out of scope, those declarations
     * disappear. When asking a "child" to retrieve a declaration, it 
     * delegates the search to its parent if it does not hold a matching
     * entry itself.
     * <p>
     * @param parent must be non-null.
     */
    public PluginManager(PluginManager parent) {
        this.parent = parent;
        this.pluginContext = parent.pluginContext;
    }
    
    //------------------- methods --------------------------------------------

    /**
     * Add the declaration to the set of known declarations.
     * <p>
     * TODO: somehow get a reference to a Digester object
     * so that we can really log here. Currently, all
     * logging is disabled from this method.
     *
     *@param decl an object representing a plugin class.
     */
    public void addDeclaration(Declaration decl) {
        Log log = LogUtils.getLogger(null);
        boolean debug = log.isDebugEnabled();
        
        Class<?> pluginClass = decl.getPluginClass();
        String id = decl.getId();
        
        declarationsByClass.put(pluginClass.getName(), decl);
            
        if (id != null) {
            declarationsById.put(id, decl);
            if (debug) {
                log.debug(
                    "Indexing plugin-id [" + id + "]" +
                    " -> class [" + pluginClass.getName() + "]");
            }
        }
    }

    /**
     * Return the declaration object with the specified class.
     * If no such plugin is known, null is returned.
     */
    public Declaration getDeclarationByClass(String className) {
        Declaration decl = 
            declarationsByClass.get(className);
            
        if ((decl == null) && (parent != null)) {
            decl = parent.getDeclarationByClass(className);
        }

        return decl;
    }

    /**
     * Return the declaration object with the specified id.
     * If no such plugin is known, null is returned.
     *
     *@param id Description of the Parameter
     *@return The declaration value
     */
    public Declaration getDeclarationById(String id) {
        Declaration decl = declarationsById.get(id);

        if ((decl == null) && (parent != null)) {
            decl = parent.getDeclarationById(id);
        }

        return decl;
    }

    /**
     * Given a plugin class and some associated properties, scan the
     * list of known RuleFinder instances until one detects a source of
     * custom rules for this plugin (aka a RuleLoader).
     * <p>
     * If no source of custom rules can be found, null is returned.
     */
    public RuleLoader findLoader(Digester digester, String id, 
                        Class<?> pluginClass, Properties props) 
                        throws PluginException {    

        // iterate over the list of RuleFinders, trying each one 
        // until one of them locates a source of dynamic rules given
        // this specific plugin class and the associated declaration 
        // properties.
        Log log = LogUtils.getLogger(digester);
        boolean debug = log.isDebugEnabled();
        log.debug("scanning ruleFinders to locate loader..");
        
        List<RuleFinder> ruleFinders = pluginContext.getRuleFinders();
        RuleLoader ruleLoader = null;
        try {
            for(Iterator<RuleFinder> i = ruleFinders.iterator(); 
                i.hasNext() && ruleLoader == null; ) {
                    
                RuleFinder finder = i.next();
                if (debug) {
                    log.debug("checking finder of type " + finder.getClass().getName());
                }
                ruleLoader = finder.findLoader(digester, pluginClass, props);
            }
        }
        catch(PluginException e) {
            throw new PluginException(
                "Unable to locate plugin rules for plugin"
                + " with id [" + id + "]"
                + ", and class [" + pluginClass.getName() + "]"
                + ":" + e.getMessage(), e.getCause());
        }
        log.debug("scanned ruleFinders.");
        
        return ruleLoader;
    }
}