IP multicasting is the transmission of IP datagrams to members of * a group that is zero or more hosts identified by a single destination * address. * *
In the case of a channel to an {@link StandardProtocolFamily#INET IPv4} socket, * the underlying operating system supports * RFC 2236: Internet Group Management Protocol, Version 2 (IGMPv2). * It may optionally support source filtering as specified by RFC 3376: Internet Group * Management Protocol, Version 3 (IGMPv3). * For channels to an {@link StandardProtocolFamily#INET6 IPv6} socket, the equivalent * standards are RFC 2710: * Multicast Listener Discovery (MLD) for IPv6 and RFC 3810: Multicast Listener * Discovery Version 2 (MLDv2) for IPv6. * *
The {@link #join(InetAddress,NetworkInterface)} method is used to * join a group and receive all multicast datagrams sent to the group. A channel * may join several multicast groups and may join the same group on several * {@link NetworkInterface interfaces}. Membership is dropped by invoking the {@link * MembershipKey#drop drop} method on the returned {@link MembershipKey}. If the * underlying platform supports source filtering then the {@link MembershipKey#block * block} and {@link MembershipKey#unblock unblock} methods can be used to block or * unblock multicast datagrams from particular source addresses. * *
The {@link #join(InetAddress,NetworkInterface,InetAddress)} method * is used to begin receiving datagrams sent to a group whose source address matches * a given source address. This method throws {@link UnsupportedOperationException} * if the underlying platform does not support source filtering. Membership is * cumulative and this method may be invoked again with the same group * and interface to allow receiving datagrams from other source addresses. The * method returns a {@link MembershipKey} that represents membership to receive * datagrams from the given source address. Invoking the key's {@link * MembershipKey#drop drop} method drops membership so that datagrams from the * source address can no longer be received. * *
The creation of the channel should specify the {@link ProtocolFamily} * that corresponds to the address type of the multicast groups that the channel * will join. There is no guarantee that a channel to a socket in one protocol * family can join and receive multicast datagrams when the address of the * multicast group corresponds to another protocol family. For example, it is * implementation specific if a channel to an {@link StandardProtocolFamily#INET6 IPv6} * socket can join an {@link StandardProtocolFamily#INET IPv4} multicast group and receive * multicast datagrams sent to the group.
The channel's socket should be bound to the {@link * InetAddress#isAnyLocalAddress wildcard} address. If the socket is bound to * a specific address, rather than the wildcard address then it is implementation * specific if multicast datagrams are received by the socket.
The {@link StandardSocketOptions#SO_REUSEADDR SO_REUSEADDR} option should be * enabled prior to {@link NetworkChannel#bind binding} the socket. This is * required to allow multiple members of the group to bind to the same * address.
Usage Example: *
* // join multicast group on this interface, and also use this
* // interface for outgoing multicast datagrams
* NetworkInterface ni = NetworkInterface.getByName("hme0");
*
* DatagramChannel dc = DatagramChannel.open(StandardProtocolFamily.INET)
* .setOption(StandardSocketOptions.SO_REUSEADDR, true)
* .bind(new InetSocketAddress(5000))
* .setOption(StandardSocketOptions.IP_MULTICAST_IF, ni);
*
* InetAddress group = InetAddress.getByName("225.4.5.6");
*
* MembershipKey key = dc.join(group, ni);
*
*
* @since 1.7
*/
public interface MulticastChannel
extends NetworkChannel
{
/**
* Closes this channel.
*
* If the channel is a member of a multicast group then the membership * is {@link MembershipKey#drop dropped}. Upon return, the {@link * MembershipKey membership-key} will be {@link MembershipKey#isValid * invalid}. * *
This method otherwise behaves exactly as specified by the {@link * Channel} interface. * * @throws IOException * If an I/O error occurs */ @Override void close() throws IOException; /** * Joins a multicast group to begin receiving all datagrams sent to the group, * returning a membership key. * *
If this channel is currently a member of the group on the given * interface to receive all datagrams then the membership key, representing * that membership, is returned. Otherwise this channel joins the group and * the resulting new membership key is returned. The resulting membership key * is not {@link MembershipKey#sourceAddress source-specific}. * *
A multicast channel may join several multicast groups, including * the same group on more than one interface. An implementation may impose a * limit on the number of groups that may be joined at the same time. * * @param group * The multicast address to join * @param interf * The network interface on which to join the group * * @return The membership key * * @throws IllegalArgumentException * If the group parameter is not a {@link InetAddress#isMulticastAddress * multicast} address, or the group parameter is an address type * that is not supported by this channel * @throws IllegalStateException * If the channel already has source-specific membership of the * group on the interface * @throws UnsupportedOperationException * If the channel's socket is not an Internet Protocol socket * @throws ClosedChannelException * If this channel is closed * @throws IOException * If an I/O error occurs * @throws SecurityException * If a security manager is set, and its * {@link SecurityManager#checkMulticast(InetAddress) checkMulticast} * method denies access to the multiast group */ MembershipKey join(InetAddress group, NetworkInterface interf) throws IOException; /** * Joins a multicast group to begin receiving datagrams sent to the group * from a given source address. * *
If this channel is currently a member of the group on the given * interface to receive datagrams from the given source address then the * membership key, representing that membership, is returned. Otherwise this * channel joins the group and the resulting new membership key is returned. * The resulting membership key is {@link MembershipKey#sourceAddress * source-specific}. * *
Membership is cumulative and this method may be invoked * again with the same group and interface to allow receiving datagrams sent * by other source addresses to the group. * * @param group * The multicast address to join * @param interf * The network interface on which to join the group * @param source * The source address * * @return The membership key * * @throws IllegalArgumentException * If the group parameter is not a {@link * InetAddress#isMulticastAddress multicast} address, the * source parameter is not a unicast address, the group * parameter is an address type that is not supported by this channel, * or the source parameter is not the same address type as the group * @throws IllegalStateException * If the channel is currently a member of the group on the given * interface to receive all datagrams * @throws UnsupportedOperationException * If the channel's socket is not an Internet Protocol socket or * source filtering is not supported * @throws ClosedChannelException * If this channel is closed * @throws IOException * If an I/O error occurs * @throws SecurityException * If a security manager is set, and its * {@link SecurityManager#checkMulticast(InetAddress) checkMulticast} * method denies access to the multiast group */ MembershipKey join(InetAddress group, NetworkInterface interf, InetAddress source) throws IOException; }