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Java Platform 1.2 Beta 4 |
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java.lang.Object | +--java.net.DatagramSocket | +--java.net.MulticastSocket
A multicast group is specified by a class D IP address, those
in the range 224.0.0.1
to 239.255.255.255
,
inclusive, and by a standard UDP port number. 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 ... byte[] msg = {'H', 'e', 'l', 'l', 'o'}; InetAddress group = InetAddress.getByName("228.5.6.7"); MulticastSocket s = new MulticastSocket(6789); s.joinGroup(group); DatagramPacket hi = new DatagramPacket(msg, 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.
Constructor Summary | |
MulticastSocket()
Create a multicast socket. |
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MulticastSocket(int port)
Create a multicast socket and bind it to a specific port. |
Method Summary | |
InetAddress | getInterface()
Retrieve the address of the network interface used for multicast packets. |
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 allows you to get time-to-live values from 0 (excluded) to 255 (included). |
void | joinGroup(InetAddress mcastaddr)
Joins a multicast group. |
void | leaveGroup(InetAddress mcastaddr)
Leave a multicast group. |
void | send(DatagramPacket p,
byte ttl)
Sends a datagram packet to the destination, with a TTL (time- to-live) other than the default for the socket. |
void | setInterface(InetAddress inf)
Set the outgoing network interface for multicast packets on this socket, to other than the system default. |
void | setTimeToLive(int ttl)
Set the default time-to-live for multicast packets sent out on this socket. |
void | setTTL(byte ttl)
Deprecated. use the setTimeToLive method instead, which allows you to set time-to-live values from 0 (excluded) to 255 (included). |
Methods inherited from class java.net.DatagramSocket | |
close , getLocalAddress , getLocalPort , getReceiveBufferSize , getSendBufferSize , getSoTimeout , receive , send , setReceiveBufferSize , setSendBufferSize , setSoTimeout |
Methods inherited from class java.lang.Object | |
clone , equals , finalize , getClass , hashCode , notify , notifyAll , toString , wait , wait , wait |
Constructor Detail |
public MulticastSocket() throws IOException
public MulticastSocket(int port) throws IOException
local
- port to useMethod Detail |
public void setTTL(byte ttl) throws IOException
DatagramPackets
sent to a MulticastGroup, which
specifies how many "hops" that the packet will be forwarded
on the network before it expires.
This method may only be used to set time-to-live value between 1 and 127. The behavior if the value is outside that range is undefined.
ttl
- the time-to-livepublic void setTimeToLive(int ttl) throws IOException
DatagramPackets
sent to a MulticastGroup, which
specifies how many "hops" that the packet will be forwarded
on the network before it expires.
The ttl is must be in the range 0 < ttl <=
255
or an IllegalArgumentException will be thrown.
ttl
- the time-to-livepublic byte getTTL() throws IOException
public int getTimeToLive() throws IOException
public void joinGroup(InetAddress mcastaddr) throws IOException
mcastaddr
- is the multicast address to joinpublic void leaveGroup(InetAddress mcastaddr) throws IOException
mcastaddr
- is the multicast address to leavepublic void setInterface(InetAddress inf) throws SocketException
public InetAddress getInterface() throws SocketException
public void send(DatagramPacket p, byte ttl) throws IOException
p
- is the packet to be sent. The packet should contain
the destination multicast ip address and the data to be sent.
One does not need to be the member of the group to send
packets to a destination multicast address.
ttl
- optional time to live for multicast packet.
default ttl is 1.DatagramSocket.send(java.net.DatagramPacket)
,
DatagramSocket.receive(java.net.DatagramPacket)
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Java Platform 1.2 Beta 4 |
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SUMMARY: INNER | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD |