Module java.base
Package java.nio.channels

Interface MulticastChannel

All Superinterfaces:
AutoCloseable, Channel, Closeable, NetworkChannel
All Known Implementing Classes:
DatagramChannel
public interface MulticastChannel extends NetworkChannel
A network channel that supports Internet Protocol (IP) multicasting.

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 IPv4 socket, the underlying operating system optionally supports RFC 2236: Internet Group Management Protocol, Version 2 (IGMPv2). When IGMPv2 is supported then the operating system may additionally support source filtering as specified by RFC 3376: Internet Group Management Protocol, Version 3 (IGMPv3). For channels to an 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 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 interfaces. Membership is dropped by invoking the drop method on the returned MembershipKey. If the underlying platform supports source filtering then the block and unblock methods can be used to block or unblock multicast datagrams from particular source addresses.

The 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 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 MembershipKey that represents membership to receive datagrams from the given source address. Invoking the key's drop method drops membership so that datagrams from the source address can no longer be received.

Platform dependencies

The multicast implementation is intended to map directly to the native multicasting facility. Consequently, the following items should be considered when developing an application that receives IP multicast datagrams:

  1. The creation of the channel should specify the 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 IPv6 socket can join an IPv4 multicast group and receive multicast datagrams sent to the group.

  2. The channel's socket should be bound to the 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.

  3. The SO_REUSEADDR option should be enabled prior to 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
External Specifications