Top Description Constructors Methods
java.net

public Class MulticastSocket

extends DatagramSocket
Class Inheritance
Known Direct Subclasses
java.net.NetMulticastSocket, sun.nio.ch.DatagramSocketAdaptor
Imports
java.io.IOException, java.nio.channels.DatagramChannel, .MulticastChannel
A MulticastSocket is a datagram socket that is convenient for sending and receiving IP multicast datagrams. The MulticastSocket constructors create a socket with appropriate socket options enabled that make it suitable for receiving multicast datagrams. The MulticastSocket class additionally defines convenient setter and getter methods for socket options that are commonly used by multicasting applications.

Joining one or more multicast groups makes it possible to receive multicast datagrams sent to these groups.

An IPv4 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 method, specifying the group address and the network interface through which multicast datagrams will be received: 

// join a Multicast group and send the group salutations
...
String msg = "Hello";
InetAddress mcastaddr = InetAddress.getByName("228.5.6.7");
InetSocketAddress group = new InetSocketAddress(mcastaddr, 6789);
NetworkInterface netIf = NetworkInterface.getByName("bge0");
MulticastSocket s = new MulticastSocket(6789);

s.joinGroup(new InetSocketAddress(mcastaddr, 0), netIf);
byte[] msgBytes = msg.getBytes(StandardCharsets.UTF_8);
DatagramPacket hi = new DatagramPacket(msgBytes, msgBytes.length, group);
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, netIf);
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(SocketAddress mcastaddr, NetworkInterface netIf) method. Multiple MulticastSockets may subscribe to a multicast group and port concurrently, and they will all receive group datagrams.

The DatagramSocket and MulticastSocket classes define convenience methods to set and get several socket options. Like DatagramSocket this class also supports the setOption and getOption methods to set and query socket options. The set of supported socket options is defined in DatagramSocket. Additional (implementation specific) options may also be supported.

API Note

DatagramSocket may be used directly for sending and receiving multicast datagrams. DatagramChannel implements the MulticastChannel interface and provides an alternative API for sending and receiving multicast datagrams. The MulticastChannel API supports both any-source and source-specific multicast. Consider using DatagramChannel for multicasting.

Author
Pavani Diwanji
Since
1.1

Constructor Summary

AccessConstructor and Description
pack-priv
MulticastSocket(MulticastSocket
the delegate, can be null.
delegate)

Create a MulticastSocket that delegates to the given delegate if not null.

public
MulticastSocket()

Constructs a multicast socket and binds it to any available port on the local host machine.

public
MulticastSocket(int
port to use
port)

Constructs a multicast socket and binds it to the specified port on the local host machine.

public
MulticastSocket(SocketAddress
Socket address to bind to, or null for an unbound socket.
bindaddr)

Creates a multicast socket, bound to the specified local socket address.

Method Summary

Modifier and TypeMethod and Description
pack-priv final MulticastSocket
delegate()

Overrides java.net.DatagramSocket.delegate.

public InetAddress

Returns:

An InetAddress representing the address of the network interface used for multicast packets, or if no interface has been set, an InetAddress representing any local address.
getInterface()
Deprecated since 14. The network interface may not be uniquely identified by the InetAddress returned. Use getNetworkInterface() instead.

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

public boolean

Returns:

true if the LoopbackMode has been disabled
getLoopbackMode()
Deprecated since 14. Use getOption(SocketOption) with java.net.StandardSocketOptions#IP_MULTICAST_LOOP instead.

Get the setting for local loopback of multicast datagrams.

public NetworkInterface

Returns:

The multicast NetworkInterface currently set. A placeholder NetworkInterface is returned when there is no interface set; it has a single InetAddress to represent any local address.
getNetworkInterface()

Get the multicast network interface set for outgoing multicast datagrams sent from this socket.

public int

Returns:

the default time-to-live value
getTimeToLive()

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

public byte

Returns:

the default time-to-live value
getTTL()
Deprecated for removal since 1.2. 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.

public void
joinGroup(InetAddress
is the multicast address to join
mcastaddr)
Deprecated since 14. This method does not accept the network interface on which to join the multicast group.

Joins a multicast group.

public void
joinGroup(SocketAddress
indicates the multicast address to join.
mcastaddr, NetworkInterface
specifies the local interface to receive multicast datagram packets, or null.
netIf)

Overrides java.net.DatagramSocket.joinGroup.

Joins a multicast group.

public void
leaveGroup(InetAddress
is the multicast address to leave
mcastaddr)
Deprecated since 14. This method does not accept the network interface on which to leave the multicast group.

Leave a multicast group.

public void
leaveGroup(SocketAddress
is the multicast address to leave. This should contain the same IP address than that used for joining the group.
mcastaddr, NetworkInterface
specifies the local interface or null to defer to the interface set for outgoing multicast datagrams. If null, and no interface has been set, the behaviour is unspecified: any interface may be selected or the operation may fail with a SocketException.
netIf)

Overrides java.net.DatagramSocket.leaveGroup.

Leave a multicast group on a specified local interface.

public void
send(DatagramPacket
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.
p, byte
optional time to live for multicast packet. default ttl is 1.
ttl)
Deprecated for removal since 1.4. Use the following code or its equivalent instead: 
......

Sends a datagram packet to the destination, with a TTL (time-to-live) other than the default for the socket.

public void
setInterface(InetAddress
the InetAddress
inf)
Deprecated since 14. The InetAddress may not uniquely identify the network interface.

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

public void
setLoopbackMode(boolean
true to disable the LoopbackMode
disable)
Deprecated since 14. Use setOption(SocketOption, Object) with java.net.StandardSocketOptions#IP_MULTICAST_LOOP instead.

Disable/Enable local loopback of multicast datagrams.

public void
setNetworkInterface(NetworkInterface
the interface
netIf)

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

public void
setTimeToLive(int
the time-to-live
ttl)

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

public void
setTTL(byte
the time-to-live
ttl)
Deprecated for removal since 1.2. use the setTimeToLive(int) 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.

Inherited from java.net.DatagramSocket:
bindcloseconnectconnectcreateDelegatedisconnectgetBroadcastgetChannelgetInetAddressgetLocalAddressgetLocalPortgetLocalSocketAddressgetOptiongetPortgetReceiveBufferSizegetRemoteSocketAddressgetReuseAddressgetSendBufferSizegetSoTimeoutgetTrafficClassisBoundisClosedisConnectedreceivesendsetBroadcastsetDatagramSocketImplFactorysetOptionsetReceiveBufferSizesetReuseAddresssetSendBufferSizesetSoTimeoutsetTrafficClasssupportedOptions

Constructor Detail

MulticastSocketback to summary
pack-priv MulticastSocket(MulticastSocket delegate)

Create a MulticastSocket that delegates to the given delegate if not null.

Parameters
delegate:MulticastSocket

the delegate, can be null.

MulticastSocketback to summary
public MulticastSocket() throws IOException

Constructs a multicast socket and binds it to any available port on the local host machine. The socket will be bound to the wildcard address.

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

Exceptions
IOException:
if an I/O exception occurs while creating the MulticastSocket
See Also
java.net.DatagramSocket#setReuseAddress(boolean), java.net.DatagramSocketImpl#setOption(SocketOption, Object)
MulticastSocketback to summary
public MulticastSocket(int port) throws IOException

Constructs a multicast socket and binds it to the specified port on the local host machine. The socket will be bound to the wildcard address.

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

Parameters
port:int

port to use

Exceptions
IOException:
if an I/O exception occurs while creating the MulticastSocket
IllegalArgumentException:
if port is out of range.
See Also
java.net.DatagramSocket#setReuseAddress(boolean)
MulticastSocketback to summary
public MulticastSocket(SocketAddress bindaddr) throws IOException

Creates a multicast socket, bound to the specified local socket address.

If the address is null an unbound socket will be created.

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

Parameters
bindaddr:SocketAddress

Socket address to bind to, or null for an unbound socket.

Exceptions
IOException:
if an I/O exception occurs while creating the MulticastSocket
Since
1.4
See Also
java.net.DatagramSocket#setReuseAddress(boolean)

Method Detail

delegateback to summary
pack-priv final MulticastSocket delegate()

Overrides java.net.DatagramSocket.delegate.

Annotations
@Override
getInterfaceback to summary
public InetAddress getInterface() throws SocketException

Deprecated

since 14.

The network interface may not be uniquely identified by the InetAddress returned. Use getNetworkInterface() instead.

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

Returns:InetAddress

An InetAddress representing the address of the network interface used for multicast packets, or if no interface has been set, an InetAddress representing any local address.

Annotations
@Deprecated
since:14
Exceptions
SocketException:
if there is an error in the underlying protocol, such as a TCP error, or the socket is closed.
See Also
setInterface(java.net.InetAddress)
getLoopbackModeback to summary
public boolean getLoopbackMode() throws SocketException

Deprecated

since 14.

Use getOption(SocketOption) with java.net.StandardSocketOptions#IP_MULTICAST_LOOP instead.

Get the setting for local loopback of multicast datagrams.

Returns:boolean

true if the LoopbackMode has been disabled

Annotations
@Deprecated
since:14
Exceptions
SocketException:
if an error occurs while getting the value, or the socket is closed.
Since
1.4
See Also
setLoopbackMode
getNetworkInterfaceback to summary
public NetworkInterface getNetworkInterface() throws SocketException

Get the multicast network interface set for outgoing multicast datagrams sent from this socket.

API Note

When an interface is set, this method is equivalent to calling getOption(StandardSocketOptions.IP_MULTICAST_IF).

Returns:NetworkInterface

The multicast NetworkInterface currently set. A placeholder NetworkInterface is returned when there is no interface set; it has a single InetAddress to represent any local address.

Exceptions
SocketException:
if there is an error in the underlying protocol, such as a TCP error, or the socket is closed.
Since
1.4
See Also
setNetworkInterface(NetworkInterface), StandardSocketOptions#IP_MULTICAST_IF
getTimeToLiveback to summary
public int getTimeToLive() throws IOException

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

API Note

This method is equivalent to calling getOption(StandardSocketOptions.IP_MULTICAST_TTL).

Returns:int

the default time-to-live value

Exceptions
IOException:
if an I/O exception occurs while getting the default time-to-live value, or the socket is closed.
Since
1.2
See Also
setTimeToLive(int), StandardSocketOptions#IP_MULTICAST_TTL
getTTLback to summary
public byte getTTL() throws IOException

Deprecated

for removal since 1.2.

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:byte

the default time-to-live value

Annotations
@Deprecated
forRemoval:true
since:1.2
Exceptions
IOException:
if an I/O exception occurs while getting the default time-to-live value, or the socket is closed.
See Also
setTTL(byte)
joinGroupback to summary
public void joinGroup(InetAddress mcastaddr) throws IOException

Deprecated

since 14.

This method does not accept the network interface on which to join the multicast group. Use joinGroup(SocketAddress, NetworkInterface) instead.

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

API Note

Calling this method is equivalent to calling joinGroup(new InetSocketAddress(mcastaddr, 0), null).

Parameters
mcastaddr:InetAddress

is the multicast address to join

Annotations
@Deprecated
since:14
Exceptions
IOException:
if there is an error joining, or when the address is not a multicast address, or the platform does not support multicasting, or the socket is closed.
joinGroupback to summary
public void joinGroup(SocketAddress mcastaddr, NetworkInterface netIf) throws IOException

Overrides java.net.DatagramSocket.joinGroup.

Doc from java.net.DatagramSocket.joinGroup.

Joins a multicast group.

In order to join a multicast group, the caller should specify the IP address of the multicast group to join, and the local network interface to receive multicast packets from.

  • The mcastaddr argument indicates the IP address of the multicast group to join. For historical reasons this is specified as a SocketAddress. The default implementation only supports InetSocketAddress and the port information is ignored.
  • The netIf argument specifies the local interface to receive multicast datagram packets, or null to defer to the interface set for outgoing multicast datagrams. If null, and no interface has been set, the behaviour is unspecified: any interface may be selected or the operation may fail with a SocketException.

It is possible to call this method several times to join several different multicast groups, or join the same group in several different networks. However, if the socket is already a member of the group, an IOException will be thrown.

Parameters
mcastaddr:SocketAddress

indicates the multicast address to join.

netIf:NetworkInterface

specifies the local interface to receive multicast datagram packets, or null.

Annotations
@Override
Exceptions
IOException:
if there is an error joining, or when the address is not a multicast address, or the platform does not support multicasting, or the socket is closed
IllegalArgumentException:
if mcastaddr is null or is a SocketAddress subclass not supported by this socket
Since
1.4
See Also
DatagramChannel#join(InetAddress, NetworkInterface), StandardSocketOptions#IP_MULTICAST_IF, setNetworkInterface(NetworkInterface), setInterface(InetAddress)
leaveGroupback to summary
public void leaveGroup(InetAddress mcastaddr) throws IOException

Deprecated

since 14.

This method does not accept the network interface on which to leave the multicast group. Use leaveGroup(SocketAddress, NetworkInterface) instead.

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

API Note

Calling this method is equivalent to calling leaveGroup(new InetSocketAddress(mcastaddr, 0), null).

Parameters
mcastaddr:InetAddress

is the multicast address to leave

Annotations
@Deprecated
since:14
Exceptions
IOException:
if there is an error leaving or when the address is not a multicast address, or the socket is closed.
leaveGroupback to summary
public void leaveGroup(SocketAddress mcastaddr, NetworkInterface netIf) throws IOException

Overrides java.net.DatagramSocket.leaveGroup.

Doc from java.net.DatagramSocket.leaveGroup.

Leave a multicast group on a specified local interface.

API Note

The mcastaddr and netIf arguments should identify a multicast group that was previously joined by this DatagramSocket.

It is possible to call this method several times to leave multiple different multicast groups previously joined, or leave the same group previously joined in multiple different networks. However, if the socket is not a member of the specified group in the specified network, an IOException will be thrown.

Parameters
mcastaddr:SocketAddress

is the multicast address to leave. This should contain the same IP address than that used for joining the group.

netIf:NetworkInterface

specifies the local interface or null to defer to the interface set for outgoing multicast datagrams. If null, and no interface has been set, the behaviour is unspecified: any interface may be selected or the operation may fail with a SocketException.

Annotations
@Override
Exceptions
IOException:
if there is an error leaving or when the address is not a multicast address, or the socket is closed.
IllegalArgumentException:
if mcastaddr is null or is a SocketAddress subclass not supported by this socket.
Since
1.4
See Also
joinGroup(SocketAddress, NetworkInterface)
sendback to summary
public void send(DatagramPacket p, byte ttl) throws IOException

Deprecated

for removal since 1.4.

Use the following code or its equivalent instead: 

......
 int ttl = mcastSocket.getOption(StandardSocketOptions.IP_MULTICAST_TTL);
 mcastSocket.setOption(StandardSocketOptions.IP_MULTICAST_TTL, newttl);
 mcastSocket.send(p);
 mcastSocket.setOption(StandardSocketOptions.IP_MULTICAST_TTL, 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.

Parameters
p:DatagramPacket

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:byte

optional time to live for multicast packet. default ttl is 1.

Annotations
@Deprecated
forRemoval:true
since:1.4
Exceptions
IOException:
if an I/O error occurs, or the socket is closed.
PortUnreachableException:
may be thrown if the socket is connected to a currently unreachable destination. Note, there is no guarantee that the exception will be thrown.
IllegalArgumentException:
if the socket is connected, and connected address and packet address differ, or if the socket is not connected and the packet address is not set or if its port is out of range.
See Also
DatagramSocket#send, DatagramSocket#receive
setInterfaceback to summary
public void setInterface(InetAddress inf) throws SocketException

Deprecated

since 14.

The InetAddress may not uniquely identify the network interface. Use setNetworkInterface(NetworkInterface) instead.

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:InetAddress

the InetAddress

Annotations
@Deprecated
since:14
Exceptions
SocketException:
if there is an error in the underlying protocol, such as a TCP error, or the socket is closed.
See Also
getInterface()
setLoopbackModeback to summary
public void setLoopbackMode(boolean disable) throws SocketException

Deprecated

since 14.

Use setOption(SocketOption, Object) with java.net.StandardSocketOptions#IP_MULTICAST_LOOP instead. The loopback mode is enabled by default, MulticastSocket.setOption(StandardSocketOptions.IP_MULTICAST_LOOP, false) disables it.

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:boolean

true to disable the LoopbackMode

Annotations
@Deprecated
since:14
Exceptions
SocketException:
if an error occurs while setting the value, or the socket is closed.
Since
1.4
See Also
getLoopbackMode
setNetworkInterfaceback to summary
public void setNetworkInterface(NetworkInterface netIf) throws SocketException

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

API Note

This method is equivalent to calling setOption(StandardSocketOptions.IP_MULTICAST_IF, netIf).

Parameters
netIf:NetworkInterface

the interface

Exceptions
SocketException:
if there is an error in the underlying protocol, such as a TCP error, or the socket is closed.
Since
1.4
See Also
getNetworkInterface(), StandardSocketOptions#IP_MULTICAST_IF
setTimeToLiveback to summary
public void setTimeToLive(int ttl) throws IOException

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.

API Note

This method is equivalent to calling setOption(StandardSocketOptions.IP_MULTICAST_TTL, ttl).

Parameters
ttl:int

the time-to-live

Exceptions
IOException:
if an I/O exception occurs while setting the default time-to-live value, or the socket is closed.
Since
1.2
See Also
getTimeToLive(), StandardSocketOptions#IP_MULTICAST_TTL
setTTLback to summary
public void setTTL(byte ttl) throws IOException

Deprecated

for removal since 1.2.

use the setTimeToLive(int) 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:byte

the time-to-live

Annotations
@Deprecated
forRemoval:true
since:1.2
Exceptions
IOException:
if an I/O exception occurs while setting the default time-to-live value, or the socket is closed.
See Also
getTTL()