Save This Page
Home » openjdk-7 » java » net » [javadoc | source]
java.net
public class: MulticastSocket [javadoc | source]
java.lang.Object
   java.net.DatagramSocket
      java.net.MulticastSocket

All Implemented Interfaces:
    Closeable

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.

Fields inherited from java.net.DatagramSocket:
impl,  oldImpl,  ST_NOT_CONNECTED,  ST_CONNECTED,  ST_CONNECTED_NO_IMPL,  connectState,  connectedAddress,  connectedPort,  implClass,  factory
Constructor:
 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
    SecurityException - if a security manager exists and its checkListen method doesn't allow the operation.
    Also see:
    SecurityManager#checkListen
    java.net.DatagramSocket#setReuseAddress(boolean)
    exception: IOException - if an I/O exception occurs while creating the MulticastSocket
    exception: SecurityException - if a security manager exists and its checkListen method doesn't allow the operation.
 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.

    Parameters:
    port - port to use
    Throws:
    IOException - if an I/O exception occurs while creating the MulticastSocket
    SecurityException - if a security manager exists and its checkListen method doesn't allow the operation.
    Also see:
    SecurityManager#checkListen
    java.net.DatagramSocket#setReuseAddress(boolean)
    exception: IOException - if an I/O exception occurs while creating the MulticastSocket
    exception: SecurityException - if a security manager exists and its checkListen method doesn't allow the operation.
 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.

    Parameters:
    bindaddr - Socket address to bind to, or null for an unbound socket.
    Throws:
    IOException - if an I/O exception occurs while creating the MulticastSocket
    SecurityException - if a security manager exists and its checkListen method doesn't allow the operation.
    Also see:
    SecurityManager#checkListen
    java.net.DatagramSocket#setReuseAddress(boolean)
    exception: IOException - if an I/O exception occurs while creating the MulticastSocket
    exception: SecurityException - if a security manager exists and its checkListen method doesn't allow the operation.
    since: 1.4 -
Method from java.net.MulticastSocket Summary:
getInterface,   getLoopbackMode,   getNetworkInterface,   getTTL,   getTimeToLive,   joinGroup,   joinGroup,   leaveGroup,   leaveGroup,   send,   setInterface,   setLoopbackMode,   setNetworkInterface,   setTTL,   setTimeToLive
Methods from java.net.DatagramSocket:
bind,   checkAddress,   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 from java.lang.Object:
clone,   equals,   finalize,   getClass,   hashCode,   notify,   notifyAll,   toString,   wait,   wait,   wait
Method from java.net.MulticastSocket Detail:
 public InetAddress getInterface() throws SocketException 
    Retrieve the address of the network interface used for multicast packets.
 public boolean getLoopbackMode() throws SocketException 
    Get the setting for local loopback of multicast datagrams.
 public NetworkInterface getNetworkInterface() throws SocketException 
    Get the multicast network interface set.
 public byte getTTL() throws IOException 
Deprecated! 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 int getTimeToLive() throws IOException 
    Get the default time-to-live for multicast packets sent out on the socket.
 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.

 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.

 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.

 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.

 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); ......

    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.

 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.
 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()

 public  void setNetworkInterface(NetworkInterface netIf) throws SocketException 
    Specify the network interface for outgoing multicast datagrams sent on this socket.
 public  void setTTL(byte ttl) throws IOException 
Deprecated! use - the setTimeToLive 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 .

 public  void setTimeToLive(int ttl) throws IOException 
    Set the default time-to-live for multicast packets sent out on this {@code MulticastSocket} in order to control the scope of the multicasts.

    The ttl must be in the range {@code 0 <= ttl <= 255} or an {@code IllegalArgumentException} will be thrown. Multicast packets sent with a TTL of {@code 0} are not transmitted on the network but may be delivered locally.