java.net
Class MulticastSocket

java.lang.Object
  |
  +--java.net.DatagramSocket
        |
        +--java.net.MulticastSocket

public class MulticastSocket

extends DatagramSocket

The multicast datagram socket class is useful for sending and receiving IP multicast packets. A MulticastSocket is a (UDP) DatagramSocket, with additional capabilities for joining "groups" of other multicast hosts on the internet.

A multicast group is specified by a class D IP address and by a standard UDP port number. Class D IP addresses are in the range 224.0.0.0 to 239.255.255.255, inclusive. The address 224.0.0.0 is reserved and should not be used.

One would join a multicast group by first creating a MulticastSocket with the desired port, then invoking the joinGroup(InetAddress groupAddr) method:

 // join a Multicast group and send the group salutations
 ...
 String msg = "Hello";
 InetAddress group = InetAddress.getByName("228.5.6.7");
 MulticastSocket s = new MulticastSocket(6789);
 s.joinGroup(group);
 DatagramPacket hi = new DatagramPacket(msg.getBytes(), msg.length(),
                             group, 6789);
 s.send(hi);
 // get their responses!
 byte[] buf = new byte[1000];
 DatagramPacket recv = new DatagramPacket(buf, buf.length);
 s.receive(recv);
 ...
 // OK, I'm done talking - leave the group...
 s.leaveGroup(group);
 

When one sends a message to a multicast group, all subscribing recipients to that host and port receive the message (within the time-to-live range of the packet, see below). The socket needn't be a member of the multicast group to send messages to it.

When a socket subscribes to a multicast group/port, it receives datagrams sent by other hosts to the group/port, as do all other members of the group and port. A socket relinquishes membership in a group by the leaveGroup(InetAddress addr) method. Multiple MulticastSocket's may subscribe to a multicast group and port concurrently, and they will all receive group datagrams.

Currently applets are not allowed to use multicast sockets.

Since:

JDK1.1

Constructor Summary
MulticastSocket()     Create a multicast socket.
MulticastSocket(int port)     Create a multicast socket and bind it to a specific port.
MulticastSocket(SocketAddress bindaddr)     Create a MulticastSocket bound to the specified socket address.

 

Method Summary
InetAddress	getInterface()     Retrieve the address of the network interface used for multicast packets.
boolean	getLoopbackMode()     Get the setting for local loopback of multicast datagrams.
NetworkInterface	getNetworkInterface()     Get the multicast network interface set.
int	getTimeToLive()     Get the default time-to-live for multicast packets sent out on the socket.
byte	getTTL()     Deprecated. use the getTimeToLive method instead, which returns an int instead of a byte.
void	joinGroup(InetAddress mcastaddr)     Joins a multicast group.
void	joinGroup(SocketAddress mcastaddr, NetworkInterface netIf)     Joins the specified multicast group at the specified interface.
void	leaveGroup(InetAddress mcastaddr)     Leave a multicast group.
void	leaveGroup(SocketAddress mcastaddr, NetworkInterface netIf)     Leave a multicast group on a specified local interface.
void	send(DatagramPacket p, byte ttl)     Deprecated. Use the following code or its equivalent instead: ...... int ttl = mcastSocket.getTimeToLive(); mcastSocket.setTimeToLive(newttl); mcastSocket.send(p); mcastSocket.setTimeToLive(ttl); ......
void	setInterface(InetAddress inf)     Set the multicast network interface used by methods whose behavior would be affected by the value of the network interface.
void	setLoopbackMode(boolean disable)     Disable/Enable local loopback of multicast datagrams The option is used by the platform's networking code as a hint for setting whether multicast data will be looped back to the local socket.
void	setNetworkInterface(NetworkInterface netIf)     Specify the network interface for outgoing multicast datagrams sent on this socket.
void	setTimeToLive(int ttl)     Set the default time-to-live for multicast packets sent out on this MulticastSocket in order to control the scope of the multicasts.
void	setTTL(byte ttl)     Deprecated. use the setTimeToLive method instead, which uses int instead of byte as the type for ttl.

 

Methods inherited from class java.net.DatagramSocket

bind, close, connect, connect, disconnect, getBroadcast, getChannel, getInetAddress, getLo