Interface SocketOptions
Interface of methods to get/set socket options. This interface is implemented by: SocketImpl and DatagramSocketImpl. Subclasses of these should override the methods of this interface in order to support their own options.
The methods and constants which specify options in this interface are for implementation only. If you’re not subclassing SocketImpl or DatagramSocketImpl, you won’t use these directly. There are type-safe methods to get/set each of these options in Socket, ServerSocket, DatagramSocket and MulticastSocket.
Field Summary
This option sets the type-of-service or traffic class field in the IP header for a TCP or UDP socket.
Fetch the local address binding of a socket (this option cannot be «set» only «gotten», since sockets are bound at creation time, and so the locally bound address cannot be changed).
When the keepalive option is set for a TCP socket and no data has been exchanged across the socket in either direction for 2 hours (NOTE: the actual value is implementation dependent), TCP automatically sends a keepalive probe to the peer.
When the OOBINLINE option is set, any TCP urgent data received on the socket will be received through the socket input stream.
Method Summary
Field Details
TCP_NODELAY
Disable Nagle’s algorithm for this connection. Written data to the network is not buffered pending acknowledgement of previously written data. Valid for TCP only: SocketImpl.
SO_BINDADDR
Fetch the local address binding of a socket (this option cannot be «set» only «gotten», since sockets are bound at creation time, and so the locally bound address cannot be changed). The default local address of a socket is INADDR_ANY, meaning any local address on a multi-homed host. A multi-homed host can use this option to accept connections to only one of its addresses (in the case of a ServerSocket or DatagramSocket), or to specify its return address to the peer (for a Socket or DatagramSocket). The parameter of this option is an InetAddress. This option must be specified in the constructor. Valid for: SocketImpl, DatagramSocketImpl
SO_REUSEADDR
Sets SO_REUSEADDR for a socket. This is used only for MulticastSockets in java, and it is set by default for MulticastSockets. Valid for: DatagramSocketImpl
SO_REUSEPORT
Sets SO_REUSEPORT for a socket. This option enables and disables the ability to have multiple sockets listen to the same address and port. Valid for: SocketImpl, DatagramSocketImpl
SO_BROADCAST
Sets SO_BROADCAST for a socket. This option enables and disables the ability of the process to send broadcast messages. It is supported for only datagram sockets and only on networks that support the concept of a broadcast message (e.g. Ethernet, token ring, etc.), and it is set by default for DatagramSockets.
IP_MULTICAST_IF
Set which outgoing interface on which to send multicast packets. Useful on hosts with multiple network interfaces, where applications want to use other than the system default. Takes/returns an InetAddress. Valid for Multicast: DatagramSocketImpl
IP_MULTICAST_IF2
Same as above. This option is introduced so that the behaviour with IP_MULTICAST_IF will be kept the same as before, while this new option can support setting outgoing interfaces with either IPv4 and IPv6 addresses. NOTE: make sure there is no conflict with this
IP_MULTICAST_LOOP
This option enables or disables local loopback of multicast datagrams. This option is enabled by default for Multicast Sockets.
IP_TOS
This option sets the type-of-service or traffic class field in the IP header for a TCP or UDP socket.
SO_LINGER
Specify a linger-on-close timeout. This option disables/enables immediate return from a close() of a TCP Socket. Enabling this option with a non-zero Integer timeout means that a close() will block pending the transmission and acknowledgement of all data written to the peer, at which point the socket is closed gracefully. Upon reaching the linger timeout, the socket is closed forcefully, with a TCP RST. Enabling the option with a timeout of zero does a forceful close immediately. If the specified timeout value exceeds 65,535 it will be reduced to 65,535. Valid only for TCP: SocketImpl
SO_TIMEOUT
ServerSocket.accept(); SocketInputStream.read(); DatagramSocket.receive();
The option must be set prior to entering a blocking operation to take effect. If the timeout expires and the operation would continue to block, java.io.InterruptedIOException is raised. The Socket is not closed in this case. Valid for all sockets: SocketImpl, DatagramSocketImpl
SO_SNDBUF
Set a hint the size of the underlying buffers used by the platform for outgoing network I/O. When used in set, this is a suggestion to the kernel from the application about the size of buffers to use for the data to be sent over the socket. When used in get, this must return the size of the buffer actually used by the platform when sending out data on this socket. Valid for all sockets: SocketImpl, DatagramSocketImpl
SO_RCVBUF
Set a hint the size of the underlying buffers used by the platform for incoming network I/O. When used in set, this is a suggestion to the kernel from the application about the size of buffers to use for the data to be received over the socket. When used in get, this must return the size of the buffer actually used by the platform when receiving in data on this socket. Valid for all sockets: SocketImpl, DatagramSocketImpl
SO_KEEPALIVE
When the keepalive option is set for a TCP socket and no data has been exchanged across the socket in either direction for 2 hours (NOTE: the actual value is implementation dependent), TCP automatically sends a keepalive probe to the peer. This probe is a TCP segment to which the peer must respond. One of three responses is expected: 1. The peer responds with the expected ACK. The application is not notified (since everything is OK). TCP will send another probe following another 2 hours of inactivity. 2. The peer responds with an RST, which tells the local TCP that the peer host has crashed and rebooted. The socket is closed. 3. There is no response from the peer. The socket is closed. The purpose of this option is to detect if the peer host crashes. Valid only for TCP socket: SocketImpl
SO_OOBINLINE
When the OOBINLINE option is set, any TCP urgent data received on the socket will be received through the socket input stream. When the option is disabled (which is the default) urgent data is silently discarded.
Method Details
setOption
Enable/disable the option specified by optID. If the option is to be enabled, and it takes an option-specific «value», this is passed in value. The actual type of value is option-specific, and it is an error to pass something that isn’t of the expected type:
SocketImpl s; . s.setOption(SO_LINGER, Integer.valueOf(10)); // OK - set SO_LINGER w/ timeout of 10 sec. s.setOption(SO_LINGER, Double.valueOf(10)); // ERROR - expects java.lang.Integer
s.setOption(TCP_NODELAY, Boolean.TRUE); // OK - enables TCP_NODELAY, a binary option
s.setOption(TCP_NODELAY, Boolean.FALSE); // OK - disables TCP_NODELAY s.setOption(SO_LINGER, Boolean.FALSE); // OK - disables SO_LINGER
For an option that has a notion of on and off, and requires a non-boolean parameter, setting its value to anything other than Boolean.FALSE implicitly enables it.
Throws SocketException if the option is unrecognized, the socket is closed, or some low-level error occurred
getOption
Fetch the value of an option. Binary options will return java.lang.Boolean.TRUE if enabled, java.lang.Boolean.FALSE if disabled, e.g.:
SocketImpl s; . Boolean noDelay = (Boolean)(s.getOption(TCP_NODELAY)); if (noDelay.booleanValue()) < // true if TCP_NODELAY is enabled. . >
For options that take a particular type as a parameter, getOption(int) will return the parameter’s value, else it will return java.lang.Boolean.FALSE:
Object o = s.getOption(SO_LINGER); if (o instanceof Integer) < System.out.print("Linger time is " + ((Integer)o).intValue()); >else < // the true type of o is java.lang.Boolean.FALSE; > Report a bug or suggest an enhancement
For further API reference and developer documentation see the Java SE Documentation, which contains more detailed, developer-targeted descriptions with conceptual overviews, definitions of terms, workarounds, and working code examples. Other versions.
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