Class MulticastSocket
- All Implemented Interfaces:
Closeable
,AutoCloseable
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 theMulticastChannel
interface and provides an alternative API for sending and receiving multicast datagrams. TheMulticastChannel
API supports both any-source and source-specific multicast. Consider usingDatagramChannel
for multicasting.- Since:
- 1.1
-
Constructor Summary
ConstructorDescriptionConstructs a multicast socket and binds it to any available port on the local host machine.MulticastSocket
(int port) Constructs a multicast socket and binds it to the specified port on the local host machine.MulticastSocket
(SocketAddress bindaddr) Creates a multicast socket, bound to the specified local socket address. -
Method Summary
Modifier and TypeMethodDescriptionDeprecated.The network interface may not be uniquely identified by the InetAddress returned.boolean
Deprecated.Get the multicast network interface set for outgoing multicast datagrams sent from this socket.int
Get the default time-to-live for multicast packets sent out on the socket.byte
getTTL()
Deprecated, for removal: This API element is subject to removal in a future version.use thegetTimeToLive()
method instead, which returns an int instead of a byte.void
joinGroup
(InetAddress mcastaddr) Deprecated.This method does not accept the network interface on which to join the multicast group.void
joinGroup
(SocketAddress mcastaddr, NetworkInterface netIf) Joins a multicast group.void
leaveGroup
(InetAddress mcastaddr) Deprecated.This method does not accept the network interface on which to leave the multicast group.void
leaveGroup
(SocketAddress mcastaddr, NetworkInterface netIf) Leave a multicast group on a specified local interface.void
send
(DatagramPacket p, byte ttl) Deprecated, for removal: This API element is subject to removal in a future version.Use the following code or its equivalent instead:void
setInterface
(InetAddress inf) Deprecated.The InetAddress may not uniquely identify the network interface.void
setLoopbackMode
(boolean disable) Deprecated.void
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 thisMulticastSocket
in order to control the scope of the multicasts.void
setTTL
(byte ttl) Deprecated, for removal: This API element is subject to removal in a future version.use thesetTimeToLive(int)
method instead, which uses int instead of byte as the type for ttl.Methods declared in class java.net.DatagramSocket
bind, close, connect, connect, disconnect, getBroadcast, getChannel, getInetAddress, getLocalAddress, getLocalPort, getLocalSocketAddress, getOption, getPort, getReceiveBufferSize, getRemoteSocketAddress, getReuseAddress, getSendBufferSize, getSoTimeout, getTrafficClass, isBound, isClosed, isConnected, receive, send, setBroadcast, setDatagramSocketImplFactory, setOption, setReceiveBufferSize, setReuseAddress, setSendBufferSize, setSoTimeout, setTrafficClass, supportedOptions
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Constructor Details
-
MulticastSocket
Constructs a multicast socket and binds it to any available port on the local host machine. The socket will be bound to thewildcard
address.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
DatagramSocket.setReuseAddress(boolean)
method is called to enable the SO_REUSEADDR socket option.- Throws:
IOException
- if an I/O exception occurs while creating the MulticastSocketSecurityException
- if a security manager exists and itscheckListen
method doesn't allow the operation.- See Also:
-
MulticastSocket
Constructs a multicast socket and binds it to the specified port on the local host machine. The socket will be bound to thewildcard
address.If there is a security manager, its
checkListen
method is first called with theport
argument as its argument to ensure the operation is allowed. This could result in a SecurityException.When the socket is created the
DatagramSocket.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 MulticastSocketSecurityException
- if a security manager exists and itscheckListen
method doesn't allow the operation.IllegalArgumentException
- if port is out of range.- See Also:
-
MulticastSocket
Creates a multicast socket, bound to the specified local socket address.If the address is
null
an unbound socket will be created.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
DatagramSocket.setReuseAddress(boolean)
method is called to enable the SO_REUSEADDR socket option.- Parameters:
bindaddr
- Socket address to bind to, ornull
for an unbound socket.- Throws:
IOException
- if an I/O exception occurs while creating the MulticastSocketSecurityException
- if a security manager exists and itscheckListen
method doesn't allow the operation.- Since:
- 1.4
- See Also:
-
-
Method Details
-
setTTL
Deprecated, for removal: This API element is subject to removal in a future version.use thesetTimeToLive(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 thisMulticastSocket
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, or the socket is closed.- See Also:
-
setTimeToLive
Set the default time-to-live for multicast packets sent out on thisMulticastSocket
in order to control the scope of the multicasts.The ttl must be in the range
0 <= ttl <= 255
or anIllegalArgumentException
will be thrown. Multicast packets sent with a TTL of0
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
- the time-to-live- Throws:
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:
-
getTTL
Deprecated, for removal: This API element is subject to removal in a future version.use thegetTimeToLive()
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, or the socket is closed.- See Also:
-
getTimeToLive
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:
- the default time-to-live value
- Throws:
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:
-
joinGroup
Deprecated.This method does not accept the network interface on which to join the multicast group. UsejoinGroup(SocketAddress, NetworkInterface)
instead.Joins a multicast group. Its behavior may be affected bysetInterface
orsetNetworkInterface
.If there is a security manager, this method first calls its
checkMulticast
method with themcastaddr
argument as its argument.- API Note:
- Calling this method is equivalent to calling
joinGroup(new InetSocketAddress(mcastaddr, 0), null)
. - 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, or the platform does not support multicasting, or the socket is closed.SecurityException
- if a security manager exists and itscheckMulticast
method doesn't allow the join.- See Also:
-
leaveGroup
Deprecated.This method does not accept the network interface on which to leave the multicast group. UseleaveGroup(SocketAddress, NetworkInterface)
instead.Leave a multicast group. Its behavior may be affected bysetInterface
orsetNetworkInterface
.If there is a security manager, this method first calls its
checkMulticast
method with themcastaddr
argument as its argument.- API Note:
- Calling this method is equivalent to calling
leaveGroup(new InetSocketAddress(mcastaddr, 0), null)
. - 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, or the socket is closed.SecurityException
- if a security manager exists and itscheckMulticast
method doesn't allow the operation.- See Also:
-
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 aSocketAddress
. The default implementation only supportsInetSocketAddress
and theport
information is ignored. - The
netIf
argument specifies the local interface to receive multicast datagram packets, ornull
to defer to the interface set for outgoing multicast datagrams. Ifnull
, and no interface has been set, the behaviour is unspecified: any interface may be selected or the operation may fail with aSocketException
.
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.If there is a security manager, this method first calls its
checkMulticast
method with themcastaddr
argument as its argument.- Overrides:
joinGroup
in classDatagramSocket
- Parameters:
mcastaddr
- indicates the multicast address to join.netIf
- specifies the local interface to receive multicast datagram packets, ornull
.- Throws:
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 closedSecurityException
- if a security manager exists and itscheckMulticast
method doesn't allow the join.IllegalArgumentException
- if mcastaddr isnull
or is a SocketAddress subclass not supported by this socket- Since:
- 1.4
- See Also:
- The
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leaveGroup
Leave a multicast group on a specified local interface.If there is a security manager, this method first calls its
checkMulticast
method with themcastaddr
argument as its argument.- Overrides:
leaveGroup
in classDatagramSocket
- API Note:
- The
mcastaddr
andnetIf
arguments should identify a multicast group that was previously joined by thisDatagramSocket
.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
- is the multicast address to leave. This should contain the same IP address than that used for joining the group.netIf
- specifies the local interface ornull
to defer to the interface set for outgoing multicast datagrams. Ifnull
, and no interface has been set, the behaviour is unspecified: any interface may be selected or the operation may fail with aSocketException
.- Throws:
IOException
- if there is an error leaving or when the address is not a multicast address, or the socket is closed.SecurityException
- if a security manager exists and itscheckMulticast
method doesn't allow the operation.IllegalArgumentException
- if mcastaddr isnull
or is a SocketAddress subclass not supported by this socket.- Since:
- 1.4
- See Also:
-
setInterface
Deprecated.The InetAddress may not uniquely identify the network interface. UsesetNetworkInterface(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
- the InetAddress- Throws:
SocketException
- if there is an error in the underlying protocol, such as a TCP error, or the socket is closed.- See Also:
-
getInterface
Deprecated.The network interface may not be uniquely identified by the InetAddress returned. UsegetNetworkInterface()
instead.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, or if no interface has been set, anInetAddress
representing any local address. - Throws:
SocketException
- if there is an error in the underlying protocol, such as a TCP error, or the socket is closed.- See Also:
-
setNetworkInterface
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
- the interface- Throws:
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
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:
- 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. - Throws:
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:
-
setLoopbackMode
Deprecated.UseDatagramSocket.setOption(SocketOption, Object)
withStandardSocketOptions.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
-true
to disable the LoopbackMode- Throws:
SocketException
- if an error occurs while setting the value, or the socket is closed.- Since:
- 1.4
- See Also:
-
getLoopbackMode
Deprecated.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, or the socket is closed.- Since:
- 1.4
- See Also:
-
send
@Deprecated(forRemoval=true, since="1.4") public void send(DatagramPacket p, byte ttl) throws IOException Deprecated, for removal: This API element is subject to removal in a future version.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 bysetInterface
.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'scheckMulticast
method withp.getAddress()
andttl
as its arguments. If the evaluation of that expression is false, this method instead calls the security manager'scheckConnect
method with argumentsp.getAddress().getHostAddress()
andp.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
- if an I/O error occurs, or the socket is closed.SecurityException
- if a security manager exists and itscheckMulticast
orcheckConnect
method doesn't allow the send.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:
-