Commons Digester example source code file (Declaration.java)

This example Commons Digester source code file (Declaration.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, init, log, not, pluginassertionfailure, pluginexception, pluginexception, properties, ruleloader, ruleloader, string, string, util

The Commons Digester Declaration.java source code

/* $Id: Declaration.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.logging.Log;
import org.apache.commons.digester.Digester;

/**
 * Represents a Class that can be instantiated by a PluginCreateRule, plus
 * info on how to load custom digester rules for mapping xml into that
 * plugged-in class.
 *
 * @since 1.6
 */
public class Declaration {
   
    /** The class of the object to be instantiated. */
    private Class<?> pluginClass;

    /** The name of the class of the object to be instantiated. */
    private String pluginClassName;
    
    /** See {@link #setId}. */ 
    private String id;
    
    /** See {@link #setProperties}. */
    private Properties properties = new Properties();
    
    /** See {@link #init}. */
    private boolean initialized = false;

    /**
     * Class which is responsible for dynamically loading this
     * plugin's rules on demand.
     */
    private RuleLoader ruleLoader = null;
    
    //---------------------- constructors ----------------------------------

    /**
     * Constructor.
     */
    public Declaration(String pluginClassName) {
        // We can't load the pluginClass at this time, because we don't
        // have a digester instance yet to load it through. So just
        // save the name away, and we'll load the Class object in the
        // init method.
        this.pluginClassName = pluginClassName;
    }
    
    /**
     * Constructor.
     */
    public Declaration(Class<?> pluginClass) {
        this.pluginClass = pluginClass;
        this.pluginClassName = pluginClass.getName();
    }
    
    /**
     * Create an instance where a fully-initialised ruleLoader instance
     * is provided by the caller instead of having the PluginManager
     * "discover" an appropriate one.
     */
    public Declaration(Class<?> pluginClass, RuleLoader ruleLoader) {
        this.pluginClass = pluginClass;
        this.pluginClassName = pluginClass.getName();
        this.ruleLoader = ruleLoader;
    }
    
    //---------------------- properties -----------------------------------

    /** 
     * The id that the user associated with a particular plugin declaration
     * in the input xml. This id is later used in the input xml to refer
     * back to the original declaration.
     * <p>
     * For plugins declared "in-line", the id is null.
     */
    public void setId(String id) {
        this.id = id;
    }
    
    /**
     * Return the id associated with this declaration. For plugins
     * declared "inline", null will be returned.
     * 
     * @return The id value. May be null.
     */
    public String getId() {
        return id;
    }

    /** 
     * Copy all (key,value) pairs in the param into the properties member of
     * this object.
     * <p>
     * The declaration properties cannot be explicit member variables,
     * because the set of useful properties a user can provide on a declaration
     * depends on what RuleFinder classes are available - and extra RuleFinders
     * can be added by the user. So here we keep a map of the settings, and
     * let the RuleFinder objects look for whatever properties they consider
     * significant.
     * <p>
     * The "id" and "class" properties are treated differently.
     */
    public void setProperties(Properties p) {
        properties.putAll(p);
    }
    
    /**
     * Return plugin class associated with this declaration.
     * 
     * @return The pluginClass.
     */
    public Class<?> getPluginClass() {
        return pluginClass;
    }

    //---------------------- methods -----------------------------------
    
    /**
     * Must be called exactly once, and must be called before any call
     * to the configure method.
     */
    public void init(Digester digester, PluginManager pm) throws PluginException {
        Log log = digester.getLogger();
        boolean debug = log.isDebugEnabled();
        if (debug) {
            log.debug("init being called!");
        }
        
        if (initialized) {
            throw new PluginAssertionFailure("Init called multiple times.");
        }

        if ((pluginClass == null) && (pluginClassName != null)) {
            try {
                // load the plugin class object
                pluginClass = 
                    digester.getClassLoader().loadClass(pluginClassName);
            } catch(ClassNotFoundException cnfe) {
                throw new PluginException(
                    "Unable to load class " + pluginClassName, cnfe);
            }
        }

        if (ruleLoader == null) {
            // the caller didn't provide a ruleLoader to the constructor,
            // so get the plugin manager to "discover" one.
            log.debug("Searching for ruleloader...");
            ruleLoader = pm.findLoader(digester, id, pluginClass, properties);
        } else {
            log.debug("This declaration has an explicit ruleLoader.");
        }
        
        if (debug) {
            if (ruleLoader == null) {
                log.debug(
                    "No ruleLoader found for plugin declaration"
                    + " id [" + id + "]"
                    + ", class [" + pluginClass.getClass().getName() + "].");
            } else {
                log.debug(
                    "RuleLoader of type [" + ruleLoader.getClass().getName()
                    + "] associated with plugin declaration"
                    + " id [" + id + "]"
                    + ", class [" + pluginClass.getClass().getName() + "].");
            }
        }
        
        initialized = true;        
    }
    
    /**
     * Attempt to load custom rules for the target class at the specified
     * pattern.
     * <p>
     * On return, any custom rules associated with the plugin class have
     * been loaded into the Rules object currently associated with the
     * specified digester object.
     */
     
    public void configure(Digester digester, String pattern)
                          throws PluginException {
        Log log = digester.getLogger();
        boolean debug = log.isDebugEnabled();
        if (debug) {
            log.debug("configure being called!");
        }
        
        if (!initialized) {
            throw new PluginAssertionFailure("Not initialized.");
        }

        if (ruleLoader != null) {
            ruleLoader.addRules(digester, pattern);
        }
    }
}