java.net
Class MulticastSocket

java.lang.Object
  |
  +--java.net.DatagramSocket
        |
        +--java.net.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 particular IP address format, those in the range 224.0.0.1 to 239.255.255.255, inclusive, and by a standard UDP port number. 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
 ...
 byte[] msg = {'H', 'e', 'l', 'l', 'o'};
 InetAddress group = InetAddress.getByName("228.5.6.7");
 MulticastSocket s = new MulticastSocket(6789);
 s.joinGroup(group);
 DatagramPacket hi = new DatagramPacket(msg, 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

Constructor Summary

MulticastSocket()
Create a multicast socket.

MulticastSocket(int port)
Create a multicast socket and bind it to a specific port.

Method Summary

int	getHOPS() Return the default hops value of the socket.
int	getInterface() Retrieve the address of the network interface used for multicast packets.
int	getTimeToLive() This method is still implemented under IPv6 for compatibility reasons.
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 HOPS other than the default for the socket.
void	setHOPS(int ttl) Set the default hops limit value for multicast packets sent out on this socket.
void	setInterface(InetAddress inf) This method is still implemented under IPv6 for compatibility reasons.
void	setInterface(int 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) This method is still implemented under IPv6 for compatibility reasons.
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, getFlowLabel, getInetAddress, getLocalAddress, getLocalPort, getNetAuthenticate, getNetEncryption, getPort, getReceiveBufferSize, getSendBufferSize, getSoTimeout, getTrafficClass, getTransportAuthenticate, getTransportEncryption, receive, send, setFlowLabel, setNetAuthenticate, setNetEncryption, setReceiveBufferSize, setSendBufferSize, setSoTimeout, setTrafficClass, setTransportAuthenticate, setTransportEncryption

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

MulticastSocket

public MulticastSocket()
                throws java.io.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.

Throws:

java.lang.SecurityException - if a security manager exists and its checkListen method doesn't allow the operation.

See Also:

SecurityManager.checkListen(int)

MulticastSocket

public MulticastSocket(int port)
                throws java.io.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.

Parameters:

port - port to use

Throws:

java.lang.SecurityException - if a security manager exists and its checkListen method doesn't allow the operation.

See Also:

SecurityManager.checkListen(int)

Method Detail

setTTL

public void setTTL(byte ttl)
            throws java.io.IOException

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

This method is still implemented under IPv6 for compatibility reasons. It simply performs a call to the setHOPS method.

Parameters:

ttl - the time-to-live

See Also:

setHOPS(int)

setTimeToLive

public void setTimeToLive(int ttl)
                   throws java.io.IOException

This method is still implemented under IPv6 for compatibility reasons. It simply performs a call to the setHOPS method.

The ttl must be in the range 0 <= ttl <= 255 or an IllegalArgumentException will be thrown.

Parameters:

ttl - the time-to-live

See Also:

setHOPS(int)

setHOPS

public void setHOPS(int ttl)
             throws java.io.IOException

Set the default hops limit value for multicast packets sent out on this socket. The HOPS sets the IP hops number for 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.

Parameters:

ttl - the hops number

getTTL

public byte getTTL()
            throws java.io.IOException

Deprecated. use the getTimeToLive method instead, which returns an int instead of a byte.

This method is still implemented under IPv6 for compatibility reasons. It simply performs a call to the getHOPS method.

See Also:

getHOPS()

getTimeToLive

public int getTimeToLive()
                  throws java.io.IOException

This method is still implemented under IPv6 for compatibility reasons. It simply performs a call to the getHOPS method.

See Also:

getHOPS()

getHOPS

public int getHOPS()
            throws java.io.IOException

Return the default hops value of the socket.

joinGroup

public void joinGroup(InetAddress mcastaddr)
               throws java.io.IOException

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

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:

java.io.IOException - if there is an error joining or when the address is not a multicast address.

java.lang.SecurityException - if a security manager exists and its checkMulticast method doesn't allow the join.

See Also:

SecurityManager.checkMulticast(InetAddress)

leaveGroup

public void leaveGroup(InetAddress mcastaddr)
                throws java.io.IOException

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

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:

java.io.IOException - if there is an error leaving or when the address is not a multicast address.

java.lang.SecurityException - if a security manager exists and its checkMulticast method doesn't allow the operation.

See Also:

SecurityManager.checkMulticast(InetAddress)

setInterface

public void setInterface(int inf)
                  throws java.net.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.

setInterface

public void setInterface(InetAddress inf)
                  throws java.net.SocketException

This method is still implemented under IPv6 for compatibility reasons. It throws a socket exception.

Throws:

java.net.SocketException - This API is no more valid.

getInterface

public int getInterface()
                 throws java.net.SocketException

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

send

public void send(DatagramPacket p,
                 byte ttl)
          throws java.io.IOException

Sends a datagram packet to the destination, with a HOPS other than the default for the socket. This method need only be used in instances where a particular HOPS is desired; otherwise it is preferable to set a HOPS once on the socket, and use that default HOPS 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 HOPS for multicast packet. default ttl is 1.

Throws:

java.io.IOException - is raised if an error occurs i.e error while setting ttl.

java.lang.SecurityException - if a security manager exists and its checkMulticast or checkConnect method doesn't allow the send.

See Also:

DatagramSocket.send(java.net.DatagramPacket), DatagramSocket.receive(java.net.DatagramPacket), SecurityManager.checkMulticast(java.net.InetAddress, byte), SecurityManager.checkConnect(java.lang.String, int)