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JavaTM 2 Platform Std. Ed. v1.3 |
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java.lang.Object | +--java.net.DatagramSocket | +--java.net.MulticastSocket
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.
Constructor Summary | |
MulticastSocket()
Create a multicast socket. |
|
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 returns an int instead of a byte. |
void |
joinGroup(InetAddress mcastaddr)
Joins a multicast group.Its behavior may be affected by setInterface . |
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 multicast network interface used by methods whose behavior would be affected by the value of the network interface. |
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 uses int instead of byte as the type for ttl. |
Methods inherited from class java.net.DatagramSocket |
close, connect, disconnect, getInetAddress, getLocalAddress, getLocalPort, getPort, getReceiveBufferSize, getSendBufferSize, getSoTimeout, receive, send, setDatagramSocketImplFactory, 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
If there is a security manager,
its checkListen
method is first called
with 0 as its argument to ensure the operation is allowed.
This could result in a SecurityException.
IOException
- if an I/O exception occurs
while creating the MulticastSocketSecurityException
- if a security manager exists and its
checkListen
method doesn't allow the operation.SecurityManager.checkListen(int)
public MulticastSocket(int port) throws IOException
If there is a security manager,
its checkListen
method is first called
with the port
argument
as its argument to ensure the operation is allowed.
This could result in a SecurityException.
port
- port to useIOException
- if an I/O exception occurs
while creating the MulticastSocketSecurityException
- if a security manager exists and its
checkListen
method doesn't allow the operation.SecurityManager.checkListen(int)
Method 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.
The ttl is an unsigned 8-bit quantity, and so must be
in the range 0 <= ttl <= 0xFF
.
ttl
- the time-to-liveIOException
- if an I/O exception occurs
while setting the default time-to-live valuegetTTL()
public 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 must be in the range 0 <= ttl <=
255
or an IllegalArgumentException will be thrown.
ttl
- the time-to-liveIOException
- if an I/O exception occurs
while setting the default time-to-live valuegetTimeToLive()
public byte getTTL() throws IOException
IOException
- if an I/O exception occurs
while getting the default time-to-live valuesetTTL(byte)
public int getTimeToLive() throws IOException
IOException
- if an I/O exception occurs while
getting the default time-to-live valuesetTimeToLive(int)
public void joinGroup(InetAddress mcastaddr) throws IOException
setInterface
.
If there is a security manager, this method first
calls its checkMulticast
method
with the mcastaddr
argument
as its argument.
mcastaddr
- is the multicast address to joinIOException
- if there is an error joining
or when the address is not a multicast address.SecurityException
- if a security manager exists and its
checkMulticast
method doesn't allow the join.SecurityManager.checkMulticast(InetAddress)
public void leaveGroup(InetAddress mcastaddr) throws IOException
setInterface
.
If there is a security manager, this method first
calls its checkMulticast
method
with the mcastaddr
argument
as its argument.
mcastaddr
- is the multicast address to leaveIOException
- if there is an error leaving
or when the address is not a multicast address.SecurityException
- if a security manager exists and its
checkMulticast
method doesn't allow the operation.SecurityManager.checkMulticast(InetAddress)
public void setInterface(InetAddress inf) throws SocketException
inf
- the InetAddressSocketException
- if there is an error in
the underlying protocol, such as a TCP error.getInterface()
public InetAddress getInterface() throws SocketException
InetAddress
representing
the address of the network interface used for
multicast packets.SocketException
- if there is an error in
the underlying protocol, such as a TCP error.setInterface(java.net.InetAddress)
public void send(DatagramPacket p, byte ttl) throws IOException
setInterface
.
If there is a security manager, this method first performs some
security checks. First, if p.getAddress().isMulticastAddress()
is true, this method calls the
security manager's checkMulticast
method
with p.getAddress()
and ttl
as its arguments.
If the evaluation of that expression is false,
this method instead calls the security manager's
checkConnect
method with arguments
p.getAddress().getHostAddress()
and
p.getPort()
. Each call to a security manager method
could result in a SecurityException if the operation is not allowed.
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.IOException
- is raised if an error occurs i.e
error while setting ttl.SecurityException
- if a security manager exists and its
checkMulticast
or checkConnect
method doesn't allow the send.DatagramSocket.send(java.net.DatagramPacket)
,
DatagramSocket.receive(java.net.DatagramPacket)
,
SecurityManager.checkMulticast(java.net.InetAddress, byte)
,
SecurityManager.checkConnect(java.lang.String, int)
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JavaTM 2 Platform Std. Ed. v1.3 |
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