- All Superinterfaces:
- AutoCloseable,- Channel,- Closeable,- NetworkChannel
- All Known Implementing Classes:
- DatagramChannel
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:- The creation of the channel should specify the - ProtocolFamilythat 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- IPv6socket can join an- IPv4multicast group and receive multicast datagrams sent to the group.
- The channel's socket should be bound to the - wildcardaddress. 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 - SO_REUSEADDRoption should be enabled prior to- bindingthe 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
- 
Method SummaryModifier and TypeMethodDescriptionvoidclose()Closes this channel.join(InetAddress group, NetworkInterface interf) Joins a multicast group to begin receiving all datagrams sent to the group, returning a membership key.join(InetAddress group, NetworkInterface interf, InetAddress source) Joins a multicast group to begin receiving datagrams sent to the group from a given source address.Methods declared in interface java.nio.channels.NetworkChannelbind, getLocalAddress, getOption, setOption, supportedOptions
- 
Method Details- 
closeCloses this channel.If the channel is a member of a multicast group then the membership is dropped. Upon return, themembership-keywill beinvalid.This method otherwise behaves exactly as specified by the Channelinterface.- Specified by:
- closein interface- AutoCloseable
- Specified by:
- closein interface- Channel
- Specified by:
- closein interface- Closeable
- Throws:
- IOException- If an I/O error occurs
 
- 
joinJoins 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 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. - Parameters:
- group- The multicast address to join
- interf- The network interface on which to join the group
- Returns:
- The membership key
- Throws:
- IllegalArgumentException- If the group parameter is not a- multicastaddress, or the group parameter is an address type that is not supported by this channel
- IllegalStateException- If the channel already has source-specific membership of the group on the interface
- UnsupportedOperationException- If the channel's socket is not an Internet Protocol socket, or the platform does not support multicasting
- ClosedChannelException- If this channel is closed
- IOException- If an I/O error occurs
- SecurityException- If a security manager is set, and its- checkMulticastmethod denies access to the multicast group
 
- 
joinMembershipKey join(InetAddress group, NetworkInterface interf, InetAddress source) 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 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. - Parameters:
- group- The multicast address to join
- interf- The network interface on which to join the group
- source- The source address
- Returns:
- The membership key
- Throws:
- IllegalArgumentException- If the group parameter is not a- multicastaddress, 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
- IllegalStateException- If the channel is currently a member of the group on the given interface to receive all datagrams
- UnsupportedOperationException- If the channel's socket is not an Internet Protocol socket, or source filtering is not supported, or the platform does not support multicasting
- ClosedChannelException- If this channel is closed
- IOException- If an I/O error occurs
- SecurityException- If a security manager is set, and its- checkMulticastmethod denies access to the multicast group
 
 
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