java.net
Class MulticastSocket

java.lang.Object
  |
  +--java.net.DatagramSocket
        |
        +--java.net.MulticastSocket

public class MulticastSocket
extends DatagramSocket

Untamed: 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
Author:
Pavani Diwanji

Field Summary
private  InetAddress infAddress
          The "last" interface set by setInterface on this MulticastSocket
private  Object infLock
          The lock on the socket's interface - used by setInterface and getInterface
private  Object ttlLock
          The lock on the socket's TTL.
 
Fields inherited from class java.net.DatagramSocket
connected, connectedAddress, connectedPort, factory, impl, implClass, oldImpl
 
Constructor Summary
MulticastSocket()
          Enabled: Create a multicast socket.
MulticastSocket(int port)
          Enabled: Create a multicast socket and bind it to a specific port.
MulticastSocket(SocketAddress bindaddr)
          Enabled: Create a MulticastSocket bound to the specified socket address.
 
Method Summary
 InetAddress getInterface()
          Enabled: Retrieve the address of the network interface used for multicast packets.
 boolean getLoopbackMode()
          Enabled: Get the setting for local loopback of multicast datagrams.
 NetworkInterface getNetworkInterface()
          Enabled: Get the multicast network interface set.
 int getTimeToLive()
          Enabled: Get the default time-to-live for multicast packets sent out on the socket.
 byte getTTL()
          Deprecated. use the getTimeToLive method instead, which returns an int instead of a byte.
 void joinGroup(InetAddress mcastaddr)
          Enabled: Joins a multicast group.
 void joinGroup(SocketAddress mcastaddr, NetworkInterface netIf)
          Enabled: Joins the specified multicast group at the specified interface.
 void leaveGroup(InetAddress mcastaddr)
          Enabled: Leave a multicast group.
 void leaveGroup(SocketAddress mcastaddr, NetworkInterface netIf)
          Enabled: Leave a multicast group on a specified local interface.
 void send(DatagramPacket p, byte ttl)
          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)
          Enabled: Set the multicast network interface used by methods whose behavior would be affected by the value of the network interface.
 void setLoopbackMode(boolean disable)
          Enabled: 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)
          Enabled: Specify the network interface for outgoing multicast datagrams sent on this socket.
 void setTimeToLive(int ttl)
          Enabled: Set the default time-to-live for multicast packets sent out on this MulticastSocket in order to control the scope of the multicasts.
 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
bind, close, connect, connect, createImpl, disconnect, getBroadcast, getChannel, getImpl, getInetAddress, getLocalAddress, getLocalPort, getLocalSocketAddress, getPort, getReceiveBufferSize, getRemoteSocketAddress, getReuseAddress, getSendBufferSize, getSoTimeout, getTrafficClass, isBound, isClosed, isConnected, receive, send, setBroadcast, setDatagramSocketImplFactory, setReceiveBufferSize, setReuseAddress, setSendBufferSize, setSoTimeout, setTrafficClass
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

ttlLock

private Object ttlLock
The lock on the socket's TTL. This is for set/getTTL and send(packet,ttl).


infLock

private Object infLock
The lock on the socket's interface - used by setInterface and getInterface


infAddress

private InetAddress infAddress
The "last" interface set by setInterface on this MulticastSocket

Constructor Detail

MulticastSocket

public MulticastSocket()
                throws IOException
Enabled: 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(true) method is called to enable the SO_REUSEADDR socket option.

See Also:
SecurityManager.checkListen(int), java.net.DatagramSocket#setReuseAddress(boolean)

MulticastSocket

public MulticastSocket(int port)
                throws IOException
Enabled: 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(true) method is called to enable the SO_REUSEADDR socket option.

Parameters:
port - port to use
See Also:
SecurityManager.checkListen(int), java.net.DatagramSocket#setReuseAddress(boolean)

MulticastSocket

public MulticastSocket(SocketAddress bindaddr)
                throws IOException
Enabled: 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(true) method is called to enable the SO_REUSEADDR socket option.

Parameters:
bindaddr - Socket address to bind to, or null for an unbound socket.
Since:
1.4
See Also:
SecurityManager.checkListen(int), java.net.DatagramSocket#setReuseAddress(boolean)
Method Detail

setTTL

public void setTTL(byte ttl)
            throws IOException
Deprecated. use the setTimeToLive method instead, which uses int instead of byte as the type for ttl.

Enabled: 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
IOException
See Also:
getTTL()

setTimeToLive

public void setTimeToLive(int ttl)
                   throws IOException
Enabled: 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.

Parameters:
ttl - the time-to-live
IOException
See Also:
getTimeToLive()

getTTL

public byte getTTL()
            throws IOException
Deprecated. use the getTimeToLive method instead, which returns an int instead of a byte.

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

Returns:
the default time-to-live value
IOException
See Also:
setTTL(byte)

getTimeToLive

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

Returns:
the default time-to-live value
IOException
See Also:
setTimeToLive(int)

joinGroup

public void joinGroup(InetAddress mcastaddr)
               throws IOException
Enabled: 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
IOException
See Also:
SecurityManager.checkMulticast(InetAddress)

leaveGroup

public void leaveGroup(InetAddress mcastaddr)
                throws IOException
Enabled: 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
IOException
See Also:
SecurityManager.checkMulticast(InetAddress)

joinGroup

public void joinGroup(SocketAddress mcastaddr,
                      NetworkInterface netIf)
               throws IOException
Enabled: 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:
IllegalArgumentException - if mcastaddr is null or is a SocketAddress subclass not supported by this socket
IOException
Since:
1.4
See Also:
SecurityManager.checkMulticast(InetAddress)

leaveGroup

public void leaveGroup(SocketAddress mcastaddr,
                       NetworkInterface netIf)
                throws IOException
Enabled: 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:
IllegalArgumentException - if mcastaddr is null or is a SocketAddress subclass not supported by this socket
IOException
Since:
1.4
See Also:
SecurityManager.checkMulticast(InetAddress)

setInterface

public void setInterface(InetAddress inf)
                  throws SocketException
Enabled: 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
SocketException
See Also:
getInterface()

getInterface

public InetAddress getInterface()
                         throws SocketException
Enabled: 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.
SocketException
See Also:
setInterface(java.net.InetAddress)

setNetworkInterface

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

Parameters:
netIf - the interface
SocketException
Since:
1.4
See Also:
getNetworkInterface()

getNetworkInterface

public NetworkInterface getNetworkInterface()
                                     throws SocketException
Enabled: Get the multicast network interface set.

Returns:
the multicast NetworkInterface currently set
SocketException
Since:
1.4
See Also:
setNetworkInterface(NetworkInterface)

setLoopbackMode

public void setLoopbackMode(boolean disable)
                     throws SocketException
Enabled: 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
Since:
1.4
See Also:
getLoopbackMode()

getLoopbackMode

public boolean getLoopbackMode()
                        throws SocketException
Enabled: 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
Since:
1.4
See Also:
setLoopbackMode(boolean)

send

public void send(DatagramPacket p,
                 byte ttl)
          throws IOException
Deprecated. Use the following code or its equivalent instead: ...... int ttl = mcastSocket.getTimeToLive(); mcastSocket.setTimeToLive(newttl); mcastSocket.send(p); mcastSocket.setTimeToLive(ttl); ......

Enabled: 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.
IOException
See Also:
DatagramSocket.send(java.net.DatagramPacket), DatagramSocket.receive(java.net.DatagramPacket), SecurityManager.checkMulticast(java.net.InetAddress, byte), SecurityManager.checkConnect(java.lang.String, int)


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