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.

Public 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.

Public 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.
byte
getTTL()
This method was deprecated. use the getTimeToLive method instead, which returns an int instead of a byte.
int
getTimeToLive()
Get the default time-to-live for multicast packets sent out on the socket.
void
joinGroup(SocketAddress mcastaddr, NetworkInterface netIf)
Joins the specified multicast group at the specified interface.
void
joinGroup(InetAddress mcastaddr)
Joins a multicast group.
void
leaveGroup(SocketAddress mcastaddr, NetworkInterface netIf)
Leave a multicast group on a specified local interface.
void
leaveGroup(InetAddress mcastaddr)
Leave a multicast group.
void
send(DatagramPacket p, byte ttl)
This method was 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
setTTL(byte ttl)
This method was deprecated. use the setTimeToLive method instead, which uses int instead of byte as the type for ttl.
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.

Inherited Method Summary

Public Constructors

public MulticastSocket ()

Create a multicast socket.

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.

When the socket is created the setReuseAddress(boolean) method is called to enable the SO_REUSEADDR socket option.

Throws
IOException if an I/O exception occurs while creating the MulticastSocket
SecurityException if a security manager exists and its checkListen method doesn't allow the operation.

public MulticastSocket (int port)

Create a multicast socket and bind it to a specific port.

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.

When the socket is created the setReuseAddress(boolean) method is called to enable the SO_REUSEADDR socket option.

Parameters
port port to use
Throws
IOException if an I/O exception occurs while creating the MulticastSocket
SecurityException if a security manager exists and its checkListen method doesn't allow the operation.

public MulticastSocket (SocketAddress bindaddr)

Create a MulticastSocket bound to the specified socket address.

Or, if the address is null, create an unbound socket.

If there is a security manager, its checkListen method is first called with the SocketAddress port as its argument to ensure the operation is allowed. This could result in a SecurityException.

When the socket is created the setReuseAddress(boolean) method is called to enable the SO_REUSEADDR socket option.

Parameters
bindaddr Socket address to bind to, or null for an unbound socket.
Throws
IOException if an I/O exception occurs while creating the MulticastSocket
SecurityException if a security manager exists and its checkListen method doesn't allow the operation.

Public Methods

public InetAddress getInterface ()

Retrieve the address of the network interface used for multicast packets.

Returns
  • An InetAddress representing the address of the network interface used for multicast packets.
Throws
SocketException if there is an error in the underlying protocol, such as a TCP error.

public boolean getLoopbackMode ()

Get the setting for local loopback of multicast datagrams.

Returns
  • true if the LoopbackMode has been disabled
Throws
SocketException if an error occurs while getting the value

public NetworkInterface getNetworkInterface ()

Get the multicast network interface set.

Returns
  • the multicast NetworkInterface currently set
Throws
SocketException if there is an error in the underlying protocol, such as a TCP error.

public byte getTTL ()

This method was deprecated.
use the getTimeToLive method instead, which returns an int instead of a byte.

Get the default time-to-live for multicast packets sent out on the socket.

Returns
  • the default time-to-live value
Throws
IOException if an I/O exception occurs while getting the default time-to-live value
See Also

public int getTimeToLive ()

Get the default time-to-live for multicast packets sent out on the socket.

Returns
  • the default time-to-live value
Throws
IOException if an I/O exception occurs while getting the default time-to-live value

public void joinGroup (SocketAddress mcastaddr, NetworkInterface netIf)

Joins the specified multicast group at the specified interface.

If there is a security manager, this method first calls its checkMulticast method with the mcastaddr argument as its argument.

Parameters
mcastaddr is the multicast address to join
netIf specifies the local interface to receive multicast datagram packets, or null to defer to the interface set by setInterface(InetAddress) or setNetworkInterface(NetworkInterface)
Throws
IOException 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.
IllegalArgumentException if mcastaddr is null or is a SocketAddress subclass not supported by this socket

public void joinGroup (InetAddress mcastaddr)

Joins a multicast group. Its behavior may be affected by setInterface or setNetworkInterface.

If there is a security manager, this method first calls its checkMulticast method with the mcastaddr argument as its argument.

Parameters
mcastaddr is the multicast address to join
Throws
IOException 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.

public void leaveGroup (SocketAddress mcastaddr, NetworkInterface netIf)

Leave a multicast group on a specified local interface.

If there is a security manager, this method first calls its checkMulticast method with the mcastaddr argument as its argument.

Parameters
mcastaddr is the multicast address to leave
netIf specifies the local interface or null to defer to the interface set by setInterface(InetAddress) or setNetworkInterface(NetworkInterface)
Throws
IOException 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.
IllegalArgumentException if mcastaddr is null or is a SocketAddress subclass not supported by this socket

public void leaveGroup (InetAddress mcastaddr)

Leave a multicast group. Its behavior may be affected by setInterface or setNetworkInterface.

If there is a security manager, this method first calls its checkMulticast method with the mcastaddr argument as its argument.

Parameters
mcastaddr is the multicast address to leave
Throws
IOException 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.

public void send (DatagramPacket p, byte ttl)

This method was deprecated.
Use the following code or its equivalent instead: ...... int ttl = mcastSocket.getTimeToLive(); mcastSocket.setTimeToLive(newttl); mcastSocket.send(p); mcastSocket.setTimeToLive(ttl); ......

Sends a datagram packet to the destination, with a TTL (time- to-live) other than the default for the socket. This method need only be used in instances where a particular TTL is desired; otherwise it is preferable to set a TTL once on the socket, and use that default TTL for all packets. This method does not alter the default TTL for the socket. Its behavior may be affected by 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.

Parameters
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.
Throws
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.

public void setInterface (InetAddress inf)

Set the multicast network interface used by methods whose behavior would be affected by the value of the network interface. Useful for multihomed hosts.

Parameters
inf the InetAddress
Throws
SocketException if there is an error in the underlying protocol, such as a TCP error.
See Also

public 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.

Because this option is a hint, applications that want to verify what loopback mode is set to should call getLoopbackMode()

Parameters
disable true to disable the LoopbackMode
Throws
SocketException if an error occurs while setting the value

public void setNetworkInterface (NetworkInterface netIf)

Specify the network interface for outgoing multicast datagrams sent on this socket.

Parameters
netIf the interface
Throws
SocketException if there is an error in the underlying protocol, such as a TCP error.

public void setTTL (byte ttl)

This method was deprecated.
use the setTimeToLive method instead, which uses int instead of byte as the type for ttl.

Set the default time-to-live for multicast packets sent out on this MulticastSocket in order to control the scope of the multicasts.

The ttl is an unsigned 8-bit quantity, and so must be in the range 0 <= ttl <= 0xFF .

Parameters
ttl the time-to-live
Throws
IOException if an I/O exception occurs while setting the default time-to-live value
See Also

public 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.

The ttl must be in the range 0 <= ttl <= 255 or an IllegalArgumentException will be thrown. Multicast packets sent with a TTL of 0 are not transmitted on the network but may be delivered locally.

Parameters
ttl the time-to-live
Throws
IOException if an I/O exception occurs while setting the default time-to-live value
See Also