baseconfig.java.svn-base

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/*
 * $Id$
 *
 * 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.struts.config;

import java.io.Serializable;

import java.util.Enumeration;
import java.util.Properties;

/**
 * <p> A abstract base class for all config classes.  Provide basic support
 * for arbitrary properties </p>
 *
 * @since Struts 1.3
 */
public abstract class BaseConfig implements Serializable {
    /**
     * Indicates if configuration of this component been completed. TODO
     * change protected to private and use methods provided by extenders?
     */
    protected boolean configured = false;

    /**
     * A map of arbitrary properties configured for this component.
     *
     * @since Struts 1.3
     */
    private Properties properties = new Properties();

    /**
     * Freeze the configuration of this action.
     */
    public void freeze() {
        configured = true;
    }

    /**
     * Throw <code>IllegalStateException</code> if configuration is frozen.
     *
     * @throws IllegalStateException if configuration is frozen
     */
    public void throwIfConfigured() {
        if (configured) {
            throw new IllegalStateException("Configuration is frozen");
        }
    }

    /**
     * <p> Set an arbitary key/value pair which can be retrieved by this
     * config class. This facility should eliminate many use cases for
     * subclassing <code>*Config</code> classes by providing a mechanism to
     * pass any amount of arbitrary configuration information into an config
     * class. <p /> This method must not be called after configuration is
     * complete, or an <code>IllegalStateException</code> will be thrown.</p>
     *
     * <p><b>Example</b>
     * <code><pre>
     * &lt;action path="/example" type="com.example.MyAction"&gt;
     *    &lt;set-property key="foo" property="bar" /&gt;
     * &lt;/action&gt;
     * </pre></code>
     * </p>
     *
     * @param key   the key by which this value will be retrieved
     * @param value the value to store with the supplied key
     * @throws IllegalStateException if this module configuration has been
     *                               frozen
     * @since Struts 1.3
     */
    public void setProperty(String key, String value) {
        throwIfConfigured();
        properties.setProperty(key, value);
    }

    /**
     * Return the property-value for the specified key, if any; otherwise
     * return <code>null</code>.
     *
     * @param key a key specified in the <code>struts-config</code> file
     * @return the value stored with the supplied key
     * @since Struts 1.3
     */
    public String getProperty(String key) {
        return properties.getProperty(key);
    }

    /**
     * <p> Return the entire set of properties configured for this object. At
     * this time, this only needs to be exposed to support inheritance, so
     * choosing a conservative access modifier ("protected"). </p>
     *
     * @return set of properties configured for this object
     */
    protected Properties getProperties() {
        return this.properties;
    }

    /**
     * Set the entire set of properties configured for this object. At this
     * time, this only needs to be exposed to support inheritance, so choosing
     * a conservative access modifier ("protected").
     */
    protected void setProperties(Properties properties) {
        this.properties = properties;
    }

    /**
     * <p>Compare the properties of this config with that of the given and
     * copy those that are not present.  This method is used by subclasses
     * that support configuration inheritance.</p>
     *
     * @param baseConfig The config object to copy properties from.
     */
    protected void inheritProperties(BaseConfig baseConfig) {
        throwIfConfigured();

        // Inherit forward properties
        Properties baseProperties = baseConfig.getProperties();
        Enumeration keys = baseProperties.propertyNames();

        while (keys.hasMoreElements()) {
            String key = (String) keys.nextElement();

            // Check if we have this property before copying it
            String value = this.getProperty(key);

            if (value == null) {
                value = baseProperties.getProperty(key);
                setProperty(key, value);
            }
        }
    }

    /**
     * <p>Return a copy of the properties held by this object.</p>
     */
    protected Properties copyProperties() {
        Properties copy = new Properties();

        Enumeration keys = properties.propertyNames();

        while (keys.hasMoreElements()) {
            String key = (String) keys.nextElement();

            copy.setProperty(key, properties.getProperty(key));
        }

        return copy;
    }
}