Module java.base
Package java.net

Class MulticastSocket

  • All Implemented Interfaces:
    Closeable, AutoCloseable

    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 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:
    1.1

    • Method Detail

      • setTTL

        @Deprecated
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 .

        Parameters:
        ttl - the time-to-live
        Throws:
        IOException - if an I/O exception occurs while setting the default time-to-live value
        See Also:
        getTTL()

      • setTimeToLive

        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. Multicast packets sent with a TTL of 0 are not transmitted on the network but may be delivered locally.

        Parameters:
        ttl - the time-to-live
        Throws:
        IOException - if an I/O exception occurs while setting the default time-to-live value
        See Also:
        getTimeToLive()

      • getTTL

        @Deprecated
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.
        Returns:
        the default time-to-live value
        Throws:
        IOException - if an I/O exception occurs while getting the default time-to-live value
        See Also:
        setTTL(byte)

      • getTimeToLive

        public int getTimeToLive​()
                  throws IOException
        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
        See Also:
        setTimeToLive(int)

      • joinGroup

        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.

        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
        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 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.

        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.
        SecurityException - if a security manager exists and its checkMulticast method doesn't allow the operation.
        See Also:
        SecurityManager.checkMulticast(InetAddress)

      • setInterface

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

      • getInterface

        public InetAddress getInterface​()
                         throws SocketException
        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.
        Throws:
        SocketException - if there is an error in the underlying protocol, such as a TCP error.
        See Also:
        setInterface(java.net.InetAddress)

      • setNetworkInterface

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

      • setLoopbackMode

        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()

        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
        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

        @Deprecated
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.

        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 - is raised if an error occurs i.e error while setting ttl.
        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)

      • supportedOptions

        public Set<SocketOption<?>> supportedOptions​()
        Description copied from class: DatagramSocket
        Returns a set of the socket options supported by this socket. This method will continue to return the set of options even after the socket has been closed.
        Overrides:
        supportedOptions in class DatagramSocket
        Returns:
        A set of the socket options supported by this socket. This set may be empty if the socket's DatagramSocketImpl cannot be created.