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JSR 356:Java API for WebSocket
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/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright (c) 2012 Oracle and/or its affiliates. All rights reserved.
 *
 * The contents of this file are subject to the terms of either the GNU
 * General Public License Version 2 only ("GPL") or the Common Development
 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License.  You can
 * obtain a copy of the License at
 * http://glassfish.java.net/public/CDDL+GPL_1_1.html
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 * language governing permissions and limitations under the License.
 *
 * When distributing the software, include this License Header Notice in each
 * file and include the License file at packager/legal/LICENSE.txt.
 *
 * GPL Classpath Exception:
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 *
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 */
package javax.websocket;

/**
 * Provider class that uses the ServiceLoader mechanism to provide
 * implementations of ServerContainer and ClientContainer.
 *
 * @author dannycoward
 */
public class ContainerProvider {
    private static String SERVER_CLASSNAME_PROPERTYNAME = "webocket.servercontainer.classname";
    private static String CLIENT_CLASSNAME_PROPERTYNAME = "webocket.clientcontainer.classname";

    /**
     * Obtains a reference to the (singletone) ServerContainer implementation.
     *
     * @return the server implementation.
     */
    public static ServerContainer getServerContainer() {
        return (ServerContainer) loadImplementation(SERVER_CLASSNAME_PROPERTYNAME);
    }

    /**
     * Obtains a reference to the (singleton) ClientContainer implementation.
     *
     * @return the client implementation.
     */
    public static ClientContainer getClientContainer() {
        return (ClientContainer) loadImplementation(CLIENT_CLASSNAME_PROPERTYNAME);
    }

    private static Object loadImplementation(String name) {
        String clName = System.getProperty(name);
        if (clName != null) {
            try {
                Class c = Class.forName(name);
                return c.newInstance();
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        }
        throw new RuntimeException("cannot find system property: " + name);
    }
}