ch.unifr.pai.twice.utils.device.client.UUID.java Source code

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Here is the source code for ch.unifr.pai.twice.utils.device.client.UUID.java

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package ch.unifr.pai.twice.utils.device.client;

/*
 * Copyright 2013 Oliver Schmid
 * 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.
 */

import com.google.gwt.dom.client.NativeEvent;
import com.google.gwt.storage.client.Storage;

/**
 * UUID holder - this class allows to identify a specific device session by the initial generation of a unique identifier (UUID) which is hold throughout the
 * whole client session and therefore can be used as a identifier for the device within the collaborative session.
 * 
 * To keep the same UUID even if the client session is interrupted (e.g. by closing the browser window), this implementation tries to store and recover the once
 * generated UUID in the HTML5 session storage if available.
 * 
 * @author Oliver Schmid
 * 
 */
public class UUID {

    /**
     * The currently valid identifier of this client device
     */
    private static String uuid;

    /**
     * If no identifier is defined, this method tries to recover it from the HTML5 session storage if available or generates a new UUID and stores it if
     * possible.
     * 
     * 
     * @return the currently valid identifier of this device (the return value is never null!)
     */
    public static String get() {
        if (uuid == null) {
            Storage s = Storage.getSessionStorageIfSupported();
            if (s != null) {
                uuid = s.getItem("ch.unifr.pai.mice.uuid");
            }
            if (uuid == null) {
                uuid = UUIDGenerator.uuid();
                if (s != null)
                    s.setItem("ch.unifr.pai.mice.uuid", uuid);
            }
        }
        return uuid;
    }

    /**
     * Creates a new unique identifier but doesn't store it as the client's identifier. This is a useful method if other components (e.g. events) need to have
     * their own unique identifier.
     * 
     * @return a new unique identifier
     */
    public static String createNew() {
        return UUIDGenerator.uuid();
    }

    /**
     * @param event
     * @return the unique identifier of an extended native event - null if the event doesn't contain device information (e.g. if they are originating from
     *         native input devices)
     */
    public native static String getUUIDForEvent(NativeEvent event)
    /*-{
       return event.uuid;
    }-*/;
}