java.net.MulticastSocket

public class java.net

MulticastSocket

Java SE 6

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.

since JDK1.1

Constructors

public

MulticastSocket() throws IOException
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 DatagramSocket#setReuseAddress(boolean) method is called to enable the SO_REUSEADDR socket option.

Throws IOException: if an I/O exception occurs while creating the MulticastSocket

Throws SecurityException: if a security manager exists and its checkListen method doesn't allow the operation.

See also checkListen, setReuseAddress(boolean)

public

MulticastSocket(int port) throws IOException
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 DatagramSocket#setReuseAddress(boolean) method is called to enable the SO_REUSEADDR socket option.

port port to use

Throws IOException: if an I/O exception occurs while creating the MulticastSocket

Throws SecurityException: if a security manager exists and its checkListen method doesn't allow the operation.

See also checkListen, setReuseAddress(boolean)

public

MulticastSocket(SocketAddress bindaddr) throws IOException
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 DatagramSocket#setReuseAddress(boolean) method is called to enable the SO_REUSEADDR socket option.

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

Throws IOException: if an I/O exception occurs while creating the MulticastSocket

Throws SecurityException: if a security manager exists and its checkListen method doesn't allow the operation.

since 1.4

See also checkListen, setReuseAddress(boolean)

Methods

public void

joinGroup(InetAddress mcastaddr) throws IOException
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.

mcastaddr is the multicast address to join

Throws IOException: if there is an error joining or when the address is not a multicast address.

Throws SecurityException: if a security manager exists and its checkMulticast method doesn't allow the join.

See also checkMulticast(InetAddress)

public void

joinGroup(SocketAddress mcastaddr, NetworkInterface netIf) throws IOException
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.

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 MulticastSocket#setInterface(InetAddress) or MulticastSocket#setNetworkInterface(NetworkInterface)

Throws IOException: if there is an error joining or when the address is not a multicast address.

Throws SecurityException: if a security manager exists and its checkMulticast method doesn't allow the join.

Throws IllegalArgumentException: if mcastaddr is null or is a SocketAddress subclass not supported by this socket

since 1.4

See also checkMulticast(InetAddress)

public void

leaveGroup(InetAddress mcastaddr) throws IOException
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.

mcastaddr is the multicast address to leave

Throws IOException: if there is an error leaving or when the address is not a multicast address.

Throws SecurityException: if a security manager exists and its checkMulticast method doesn't allow the operation.

See also checkMulticast(InetAddress)

public void

leaveGroup(SocketAddress mcastaddr, NetworkInterface netIf) throws IOException
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.

mcastaddr is the multicast address to leave

netIf specifies the local interface or null to defer to the interface set by MulticastSocket#setInterface(InetAddress) or MulticastSocket#setNetworkInterface(NetworkInterface)

Throws IOException: if there is an error leaving or when the address is not a multicast address.

Throws SecurityException: if a security manager exists and its checkMulticast method doesn't allow the operation.

Throws IllegalArgumentException: if mcastaddr is null or is a SocketAddress subclass not supported by this socket

since 1.4

See also checkMulticast(InetAddress)

public void

send(DatagramPacket p, byte ttl) throws IOException

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.

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.

Throws SecurityException: if a security manager exists and its checkMulticast or checkConnect method doesn't allow the send.

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

See also send, receive, checkMulticast(java.net.InetAddress, byte), checkConnect

Properties

public void

setInterface(InetAddress inf) throws SocketException
Set the multicast network interface used by methods whose behavior would be affected by the value of the network interface. Useful for multihomed hosts.

inf	the InetAddress
Throws	SocketException: if there is an error in the underlying protocol, such as a TCP error.
See also	getInterface()

public InetAddress

getInterface() throws SocketException
Retrieve the address of the network interface used for multicast packets.

return	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.
See also	setInterface(java.net.InetAddress)

public void

setLoopbackMode(boolean disable) throws SocketException
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()

disable true to disable the LoopbackMode

Throws SocketException: if an error occurs while setting the value

since 1.4

See also getLoopbackMode

public boolean

getLoopbackMode() throws SocketException
Get the setting for local loopback of multicast datagrams.

Throws	SocketException: if an error occurs while getting the value
return	true if the LoopbackMode has been disabled
since	1.4
See also	setLoopbackMode

public void

setNetworkInterface(NetworkInterface netIf) throws SocketException
Specify the network interface for outgoing multicast datagrams sent on this socket.

netIf	the interface
Throws	SocketException: if there is an error in the underlying protocol, such as a TCP error.
since	1.4
See also	getNetworkInterface()

public NetworkInterface

getNetworkInterface() throws SocketException
Get the multicast network interface set.

Throws	SocketException: if there is an error in the underlying protocol, such as a TCP error.
return	the multicast `NetworkInterface` currently set
since	1.4
See also	setNetworkInterface(NetworkInterface)

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.

Throws IOException: if an I/O exception occurs while setting the default time-to-live value

ttl the time-to-live

See also getTimeToLive()

public int

getTimeToLive() throws IOException
Get the default time-to-live for multicast packets sent out on the socket.

Throws	IOException: if an I/O exception occurs while getting the default time-to-live value
return	the default time-to-live value
See also	setTimeToLive(int)

public void

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

ttl the time-to-live

Throws IOException: if an I/O exception occurs while setting the default time-to-live value

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

See also getTTL()

public byte

getTTL() throws IOException

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

Throws	IOException: if an I/O exception occurs while getting the default time-to-live value
return	the default time-to-live value
deprecated	use the getTimeToLive method instead, which returns an int instead of a byte.
See also	setTTL(byte)

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Java SE 6

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