Java tutorial
/* * Copyright (c) 2007, 2013, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.nio.channels; import java.net.InetAddress; import java.net.NetworkInterface; import java.io.IOException; /** * A token representing the membership of an Internet Protocol (IP) multicast * group. * * <p> A membership key may represent a membership to receive all datagrams sent * to the group, or it may be <em>source-specific</em>, meaning that it * represents a membership that receives only datagrams from a specific source * address. Whether or not a membership key is source-specific may be determined * by invoking its {@link #sourceAddress() sourceAddress} method. * * <p> A membership key is valid upon creation and remains valid until the * membership is dropped by invoking the {@link #drop() drop} method, or * the channel is closed. The validity of the membership key may be tested * by invoking its {@link #isValid() isValid} method. * * <p> Where a membership key is not source-specific and the underlying operation * system supports source filtering, then the {@link #block block} and {@link * #unblock unblock} methods can be used to block or unblock multicast datagrams * from particular source addresses. * * @see MulticastChannel * * @since 1.7 */ public abstract class MembershipKey { /** * Initializes a new instance of this class. */ protected MembershipKey() { } /** * Tells whether or not this membership is valid. * * <p> A multicast group membership is valid upon creation and remains * valid until the membership is dropped by invoking the {@link #drop() drop} * method, or the channel is closed. * * @return {@code true} if this membership key is valid, {@code false} * otherwise */ public abstract boolean isValid(); /** * Drop membership. * * <p> If the membership key represents a membership to receive all datagrams * then the membership is dropped and the channel will no longer receive any * datagrams sent to the group. If the membership key is source-specific * then the channel will no longer receive datagrams sent to the group from * that source address. * * <p> After membership is dropped it may still be possible to receive * datagrams sent to the group. This can arise when datagrams are waiting to * be received in the socket's receive buffer. After membership is dropped * then the channel may {@link MulticastChannel#join join} the group again * in which case a new membership key is returned. * * <p> Upon return, this membership object will be {@link #isValid() invalid}. * If the multicast group membership is already invalid then invoking this * method has no effect. Once a multicast group membership is invalid, * it remains invalid forever. */ public abstract void drop(); /** * Block multicast datagrams from the given source address. * * <p> If this membership key is not source-specific, and the underlying * operating system supports source filtering, then this method blocks * multicast datagrams from the given source address. If the given source * address is already blocked then this method has no effect. * After a source address is blocked it may still be possible to receive * datagrams from that source. This can arise when datagrams are waiting to * be received in the socket's receive buffer. * * @param source * The source address to block * * @return This membership key * * @throws IllegalArgumentException * If the {@code source} parameter is not a unicast address or * is not the same address type as the multicast group * @throws IllegalStateException * If this membership key is source-specific or is no longer valid * @throws UnsupportedOperationException * If the underlying operating system does not support source * filtering * @throws IOException * If an I/O error occurs */ public abstract MembershipKey block(InetAddress source) throws IOException; /** * Unblock multicast datagrams from the given source address that was * previously blocked using the {@link #block(InetAddress) block} method. * * @param source * The source address to unblock * * @return This membership key * * @throws IllegalStateException * If the given source address is not currently blocked or the * membership key is no longer valid */ public abstract MembershipKey unblock(InetAddress source); /** * Returns the channel for which this membership key was created. This * method will continue to return the channel even after the membership * becomes {@link #isValid invalid}. * * @return the channel */ public abstract MulticastChannel channel(); /** * Returns the multicast group for which this membership key was created. * This method will continue to return the group even after the membership * becomes {@link #isValid invalid}. * * @return the multicast group */ public abstract InetAddress group(); /** * Returns the network interface for which this membership key was created. * This method will continue to return the network interface even after the * membership becomes {@link #isValid invalid}. * * @return the network interface */ public abstract NetworkInterface networkInterface(); /** * Returns the source address if this membership key is source-specific, * or {@code null} if this membership is not source-specific. * * @return The source address if this membership key is source-specific, * otherwise {@code null} */ public abstract InetAddress sourceAddress(); }