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.
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.
IOException
- if an I/O exception occurs while creating the MulticastSocketSecurityException
- if a security manager exists and its checkListen
method doesn't allow the operation.SecurityManager.checkListen(int)
, DatagramSocket.setReuseAddress(boolean)
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.
port
- port to useIOException
- if an I/O exception occurs while creating the MulticastSocketSecurityException
- if a security manager exists and its checkListen
method doesn't allow the operation.SecurityManager.checkListen(int)
, DatagramSocket.setReuseAddress(boolean)
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.
bindaddr
- Socket address to bind to, or null
for an unbound socket.IOException
- if an I/O exception occurs while creating the MulticastSocketSecurityException
- if a security manager exists and its checkListen
method doesn't allow the operation.SecurityManager.checkListen(int)
, DatagramSocket.setReuseAddress(boolean)
@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
.
ttl
- the time-to-liveIOException
- if an I/O exception occurs while setting the default time-to-live valuegetTTL()
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.
ttl
- the time-to-liveIOException
- if an I/O exception occurs while setting the default time-to-live valuegetTimeToLive()
@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.
IOException
- if an I/O exception occurs while getting the default time-to-live valuesetTTL(byte)
public int getTimeToLive() throws IOException
Get the default time-to-live for multicast packets sent out on the socket.
IOException
- if an I/O exception occurs while getting the default time-to-live valuesetTimeToLive(int)
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.
mcastaddr
- is the multicast address to joinIOException
- if there is an error joining or when the address is not a multicast address.SecurityException
- if a security manager exists and its checkMulticast
method doesn't allow the join.SecurityManager.checkMulticast(InetAddress)
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.
mcastaddr
- is the multicast address to leaveIOException
- 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.SecurityManager.checkMulticast(InetAddress)
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.
mcastaddr
- is the multicast address to joinnetIf
- specifies the local interface to receive multicast datagram packets, or null to defer to the interface set by setInterface(InetAddress)
or setNetworkInterface(NetworkInterface)
IOException
- if there is an error joining or when the address is not a multicast address.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 socketSecurityManager.checkMulticast(InetAddress)
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.
mcastaddr
- is the multicast address to leavenetIf
- specifies the local interface or null to defer to the interface set by setInterface(InetAddress)
or setNetworkInterface(NetworkInterface)
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 socketSecurityManager.checkMulticast(InetAddress)
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.
inf
- the InetAddressSocketException
- if there is an error in the underlying protocol, such as a TCP error.getInterface()
public InetAddress getInterface() throws SocketException
Retrieve the address of the network interface used for multicast packets.
InetAddress
representing the address of the network interface used for multicast packets.SocketException
- if there is an error in the underlying protocol, such as a TCP error.setInterface(java.net.InetAddress)
public void setNetworkInterface(NetworkInterface netIf) throws SocketException
Specify the network interface for outgoing multicast datagrams sent on this socket.
netIf
- the interfaceSocketException
- if there is an error in the underlying protocol, such as a TCP error.getNetworkInterface()
public NetworkInterface getNetworkInterface() throws SocketException
Get the multicast network interface set.
NetworkInterface
currently setSocketException
- if there is an error in the underlying protocol, such as a TCP error.setNetworkInterface(NetworkInterface)
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()
disable
- true
to disable the LoopbackModeSocketException
- if an error occurs while setting the valuegetLoopbackMode()
public boolean getLoopbackMode() throws SocketException
Get the setting for local loopback of multicast datagrams.
SocketException
- if an error occurs while getting the valuesetLoopbackMode(boolean)
@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.
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
- 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.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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