Module java.base
Package java.net

Class MulticastSocket

java.lang.Object
java.net.DatagramSocket
java.net.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 mcastaddr = InetAddress.getByName("228.5.6.7");
 InetSocketAddress group = new InetSocketAddress(mcastaddr, port);
 NetworkInterface netIf = NetworkInterface.getByName("bge0");
 MulticastSocket s = new MulticastSocket(6789);

 s.joinGroup(group, netIf);
 byte[] msgBytes = msg.getBytes(StandardCharsets.UTF_8);
 DatagramPacket hi = new DatagramPacket(msgBytes, msgBytes.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, netIf);
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(SocketAddress mcastaddr, NetworkInterface netIf) method. Multiple MulticastSockets may subscribe to a multicast group and port concurrently, and they will all receive group datagrams.

The DatagramSocket and MulticastSocket classes define convenience methods to set and get several socket options. Like DatagramSocket this class also supports the setOption and getOption methods to set and query socket options. In addition to the socket options supported by DatagramSocket, a MulticastSocket supports the following socket options:

Socket options
Option Name Description
IP_MULTICAST_IF The network interface for Internet Protocol (IP) multicast datagrams
IP_MULTICAST_TTL The time-to-live for Internet Protocol (IP) multicast datagrams
IP_MULTICAST_LOOP Loopback for Internet Protocol (IP) multicast datagrams
Additional (implementation specific) options may also be supported.
API Note:
DatagramChannel implements the MulticastChannel interface and provides an alternative API for sending and receiving multicast datagrams. The MulticastChannel API supports both any-source and source-specific multicast.
Since:
1.1

  • Constructor Details

  • Method Details

    • 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
      Since:
      1.2
      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
      Since:
      1.2
      See Also:
      setTimeToLive(int)

    • joinGroup

      @Deprecated(since="14") public void joinGroup​(InetAddress mcastaddr) throws IOException
      Deprecated.
      This method does not accept the network interface on which to join the multicast group. Use joinGroup(SocketAddress, NetworkInterface) instead.
      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

      @Deprecated(since="14") public void leaveGroup​(InetAddress mcastaddr) throws IOException
      Deprecated.
      This method does not accept the network interface on which to leave the multicast group. Use leaveGroup(SocketAddress, NetworkInterface) instead.
      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)

    • joinGroup

      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.

      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). If null, and no interface has been set, the behaviour is unspecified: any interface may be selected or the operation may fail with a SocketException.
      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.
      IllegalArgumentException - if mcastaddr is null or is a SocketAddress subclass not supported by this socket
      Since:
      1.4
      See Also:
      SecurityManager.checkMulticast(InetAddress), MulticastChannel.join(InetAddress, NetworkInterface)

    • leaveGroup

      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.

      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). If null, and no interface has been set, the behaviour is unspecified: any interface may be selected or the operation may fail with a SocketException.
      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.
      IllegalArgumentException - if mcastaddr is null or is a SocketAddress subclass not supported by this socket.
      Since:
      1.4
      See Also:
      SecurityManager.checkMulticast(InetAddress)

    • setInterface

      @Deprecated(since="14") public void setInterface​(InetAddress inf) throws SocketException
      Deprecated.
      The InetAddress may not uniquely identify the network interface. Use setNetworkInterface(NetworkInterface) instead.
      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

      @Deprecated(since="14") public InetAddress getInterface() throws SocketException
      Deprecated.
      The network interface may not be uniquely identified by the InetAddress returned. Use getNetworkInterface() instead.
      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, or if no interface has been set, an InetAddress representing any local address.
      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()

    • getNetworkInterface

      public NetworkInterface getNetworkInterface() throws SocketException
      Get the multicast network interface set.
      Returns:
      The multicast NetworkInterface currently set. A placeholder NetworkInterface is returned when there is no interface set; it has a single InetAddress to represent any local address.
      Throws:
      SocketException - if there is an error in the underlying protocol, such as a TCP error.
      Since:
      1.4
      See Also:
      setNetworkInterface(NetworkInterface)

    • setLoopbackMode

      @Deprecated(since="14") public void setLoopbackMode​(boolean disable) throws SocketException
      Deprecated.
      Use DatagramSocket.setOption(SocketOption, Object) with StandardSocketOptions.IP_MULTICAST_LOOP instead. The loopback mode is enabled by default, MulticastSocket.setOption(StandardSocketOptions.IP_MULTICAST_LOOP, false) disables it.
      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

      @Deprecated(since="14") public boolean getLoopbackMode() throws SocketException
      Deprecated.
      Use DatagramSocket.getOption(SocketOption) with StandardSocketOptions.IP_MULTICAST_LOOP instead.
      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.
      PortUnreachableException - may be thrown if the socket is connected to a currently unreachable destination. Note, there is no guarantee that the exception will be thrown.
      IllegalArgumentException - if the socket is connected, and connected address and packet address differ, or if the socket is not connected and the packet address is not set or if its port is out of range.
      See Also:
      DatagramSocket.send(java.net.DatagramPacket), DatagramSocket.receive(java.net.DatagramPacket), SecurityManager.checkMulticast(java.net.InetAddress, byte), SecurityManager.checkConnect(java.lang.String, int)