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Type-safe access to Java system properties
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/*
// Licensed to Julian Hyde under one or more contributor license
// agreements. See the NOTICE file distributed with this work for
// additional information regarding copyright ownership.
//
// Julian Hyde 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.eigenbase.util.property;

import java.io.*;

import java.util.*;
import java.util.logging.*;


/**
 * Definition and accessor for a string property that is capable of storing
 * itself in a .properties file.
 *
 * @author Stephan Zuercher
 * @version $Id$
 * @since December 3, 2004
 */
public class PersistentStringProperty
    extends StringProperty
{
    //~ Static fields/initializers ---------------------------------------------

    // NOTE jvs 2-Oct-2005:  have to avoid dragging in dependencies.
    /*
    private static final Logger tracer = EigenbaseTrace.getPropertyTracer();
     */
    private static final Logger tracer =
        Logger.getLogger(Property.class.getName());

    //~ Instance fields --------------------------------------------------------

    private StringProperty propertyFileLocation;
    private PersistentPropertyStorage storage;
    private boolean storageInitialized;

    //~ Constructors -----------------------------------------------------------

    /**
     * Creates a persistent string property.
     *
     * @param properties Properties object which holds values for this property.
     * @param path Name by which this property is serialized to a properties
     * file, for example "com.acme.trace.Verbosity".
     * @param defaultValue Default value, null if there is no default.
     * @param propertyFileLocation Location of the property file where this
     * property's value should be persisted.
     */
    public PersistentStringProperty(
        Properties properties,
        String path,
        String defaultValue,
        StringProperty propertyFileLocation)
    {
        super(properties, path, defaultValue);

        // Delay initialization of storage: the property file location
        // may not be initialized until later (e.g. its value may change
        // in the constructor of the given properties object).
        this.propertyFileLocation = propertyFileLocation;
        this.storage = null;
        this.storageInitialized = false;
    }

    //~ Methods ----------------------------------------------------------------

    /**
     * Sets the value of this property.
     *
     * This method is synchronized to prevent multiple threads from
     * attempting to initialize the property storage ({@link #storage})
     * simultaneously.
     *
     * @return The previous value, or the default value if not set.
     */
    public synchronized String set(String value)
    {
        final String prevValue = super.set(value);

        if (!storageInitialized) {
            storageInitialized = true;

            if (propertyFileLocation.get() == null) {
                tracer.warning(
                    "Cannot store property '" + getPath()
                    + "' because storage location is not set");
                return prevValue;
            }
            try {
                storage =
                    PersistentPropertyStorage.newPersistentPropertyStorage(
                        propertyFileLocation.get());
            } catch (IOException e) {
                tracer.warning(
                    "Unable to initialize persistent property storage for '"
                    + getPath() + "'");
                tracer.throwing("PersistentPropertyStorage", "", e);
                return prevValue;
            }
        }

        if (storage != null) {
            try {
                storage.storeProperty(this);
            } catch (IOException e) {
                tracer.warning(
                    "Unable to persist property '" + getPath() + "'");
                tracer.throwing("PersistentPropertyStorage", "set(String)", e);
            }
        }
        return prevValue;
    }
}

// End PersistentStringProperty.java