source: trunk/java-utils/src/main/java/de/ugoe/cs/util/console/GlobalDataContainer.java @ 927

//   Copyright 2012 Georg-August-Universität Göttingen, Germany
//
//   Licensed 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 de.ugoe.cs.util.console;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;

/**
 * <p>
 * This data structure can be used by the commands to store any {@link Object}.
 * The data is stored in a key-value map, with strings as keys.
 * </p>
 * <p>
 * This class is implemented as a singleton, as more than one data container
 * does not serves no purpose.
 * </p>
 * 
 * @author Steffen Herbold
 * @version 1.0
 */
public class GlobalDataContainer implements Serializable {

        /**
         * <p>
         * Id for object serialization.
         * </p>
         */
        private static final long serialVersionUID = 1L;

        /**
         * <p>
         * Instance of the {@link GlobalDataContainer} (implemented as singleton).
         * </p>
         */
        transient private static GlobalDataContainer theInstance = null;

        /**
         * <p>
         * Internal storage of the data.
         * </p>
         */
        private Map<String, Object> dataObjects;

        /**
         * <p>
         * Returns the instance of the container. If it does not yet exist, the data
         * container is created.
         * </p>
         * 
         * @return instance of the container
         */
        public static GlobalDataContainer getInstance() {
                if (theInstance == null) {
                        theInstance = new GlobalDataContainer();
                }
                return theInstance;
        }

        /**
         * <p>
         * Manual serialization of the object. Necessary to guarantee the singleton
         * property.
         * </p>
         * 
         * @param s
         *            output stream for the serialization
         * @throws IOException
         *             thrown if there is problem writing to the output stream
         */
        private void writeObject(ObjectOutputStream s) throws IOException {
                s.defaultWriteObject();
                s.writeObject(dataObjects);
        }

        /**
         * <p>
         * Manual de-serialization of the object. Necessary to guarantee the
         * singleton property.
         * 
         * @param s
         *            input stream for the de-serialization
         * @throws IOException
         *             thrown if there is problem reading from the input stream
         * @throws ClassNotFoundException
         *             thrown if there is a problem reading from the input stream
         */
        @SuppressWarnings("unchecked")
        private void readObject(ObjectInputStream s) throws IOException,
                        ClassNotFoundException {
                s.defaultReadObject();
                if (theInstance == null) {
                        theInstance = new GlobalDataContainer();
                }
                theInstance.dataObjects = (Map<String, Object>) s.readObject();
        }

        /**
         * <p>
         * Manual de-serialization to guarantee the singleton property.
         * </p>
         * 
         * @return instance of the container
         */
        private Object readResolve() {
                return theInstance;
        }

        /**
         * <p>
         * Constructor. Creates a new GlobalDataContainer. Private to guarantee the
         * singleton property.
         * </p>
         */
        private GlobalDataContainer() {
                dataObjects = new HashMap<String, Object>();
        }

        /**
         * <p>
         * Adds data to the container.
         * </p>
         * 
         * @param key
         *            key that identifies the data
         * @param data
         *            data that is stored
         * @return true, if an old entry was overwritten; false otherwise
         */
        public boolean addData(String key, Object data) {
                Object previousEntry = dataObjects.put(key, data);
                return previousEntry != null;
        }

        /**
         * <p>
         * Removes data from the container.
         * </p>
         * 
         * @param key
         *            key of the data to be removed
         * @return true, if the object was removed; false if it was not present
         */
        public boolean removeData(String key) {
                Object previousEntry = dataObjects.remove(key);
                return previousEntry != null;
        }

        /**
         * <p>
         * Returns the data associated with a key or {@code null} if no data is
         * stored for the key.
         * </p>
         * 
         * @param key
         *            key whose data is returned
         * @return data associated with the key; {@code null} if no data is
         *         available
         */
        public Object getData(String key) {
                return dataObjects.get(key);
        }

        /**
         * <p>
         * Resets the data container, i.e., deletes all its contents.
         * </p>
         */
        public void reset() {
                dataObjects = new HashMap<String, Object>();
        }

        /**
         * <p>
         * Returns the keys of all objects contained in the storage.
         * </p>
         * 
         * @return keys of all objects in the storage
         */
        public Collection<String> getAllKeys() {
                return dataObjects.keySet();
        }

}