DefaultDatagramSocketImplFactory.java

/*
 * Copyright (c) 2007, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */
package java.net;

import java.security.AccessController;
import java.security.PrivilegedAction;

/**
 * This class defines a factory for creating DatagramSocketImpls. It defaults
 * to creating plain DatagramSocketImpls, but may create other DatagramSocketImpls
 * by setting the impl.prefix system property.
 *
 * For Windows versions lower than Windows Vista a TwoStacksPlainDatagramSocketImpl
 * is always created. This impl supports IPv6 on these platform where available.
 *
 * On Windows platforms greater than Vista that support a dual layer TCP/IP stack
 * a DualStackPlainDatagramSocketImpl is created for DatagramSockets. For MulticastSockets
 * a TwoStacksPlainDatagramSocketImpl is always created. This is to overcome the lack
 * of behavior defined for multicasting over a dual layer socket by the RFC.
 *
 * @author Chris Hegarty
 */

class DefaultDatagramSocketImplFactory
{
    static Class<?> prefixImplClass = null;

    /* the windows version. */
    private static float version;

    /* java.net.preferIPv4Stack */
    private static boolean preferIPv4Stack = false;

    /* If the version supports a dual stack TCP implementation */
    private static boolean useDualStackImpl = false;

    /* sun.net.useExclusiveBind */
    private static String exclBindProp;

    /* True if exclusive binding is on for Windows */
    private static boolean exclusiveBind = true;


    static {
        // Determine Windows Version.
        java.security.AccessController.doPrivileged(
                new PrivilegedAction<Object>() {
                    public Object run() {
                        version = 0;
                        try {
                            version = Float.parseFloat(System.getProperties()
                                    .getProperty("os.version"));
                            preferIPv4Stack = Boolean.parseBoolean(
                                              System.getProperties()
                                              .getProperty(
                                                   "java.net.preferIPv4Stack"));
                            exclBindProp = System.getProperty(
                                    "sun.net.useExclusiveBind");
                        } catch (NumberFormatException e ) {
                            assert false : e;
                        }
                        return null; // nothing to return
                    }
                });

        // (version >= 6.0) implies Vista or greater.
        if (version >= 6.0 && !preferIPv4Stack) {
                useDualStackImpl = true;
        }
        if (exclBindProp != null) {
            // sun.net.useExclusiveBind is true
            exclusiveBind = exclBindProp.length() == 0 ? true
                    : Boolean.parseBoolean(exclBindProp);
        } else if (version < 6.0) {
            exclusiveBind = false;
        }

        // impl.prefix
        String prefix = null;
        try {
            prefix = AccessController.doPrivileged(
                new sun.security.action.GetPropertyAction("impl.prefix", null));
            if (prefix != null)
                prefixImplClass = Class.forName("java.net."+prefix+"DatagramSocketImpl");
        } catch (Exception e) {
            System.err.println("Can't find class: java.net." +
                                prefix +
                                "DatagramSocketImpl: check impl.prefix property");
        }
    }

    /**
     * Creates a new <code>DatagramSocketImpl</code> instance.
     *
     * @param   isMulticast true if this impl is to be used for a MutlicastSocket
     * @return  a new instance of <code>PlainDatagramSocketImpl</code>.
     */
    static DatagramSocketImpl createDatagramSocketImpl(boolean isMulticast)
        throws SocketException {
        if (prefixImplClass != null) {
            try {
                return (DatagramSocketImpl) prefixImplClass.newInstance();
            } catch (Exception e) {
                throw new SocketException("can't instantiate DatagramSocketImpl");
            }
        } else {
            if (isMulticast)
                exclusiveBind = false;
            if (useDualStackImpl && !isMulticast)
                return new DualStackPlainDatagramSocketImpl(exclusiveBind);
            else
                return new TwoStacksPlainDatagramSocketImpl(exclusiveBind);
        }
    }
}