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Java Standard Edition (SE)

SocketOptions


compact1, compact2, compact3
java.net

Interface SocketOptions

  • All Known Implementing Classes:
    DatagramSocketImpl, SocketImpl


    public 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

      Fields 
      Modifier and Type Field and Description
      static int IP_MULTICAST_IF
      Set which outgoing interface on which to send multicast packets.
      static int IP_MULTICAST_IF2
      Same as above.
      static int IP_MULTICAST_LOOP
      This option enables or disables local loopback of multicast datagrams.
      static int IP_TOS
      This option sets the type-of-service or traffic class field in the IP header for a TCP or UDP socket.
      static int 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).
      static int SO_BROADCAST
      Sets SO_BROADCAST for a socket.
      static int 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.
      static int SO_LINGER
      Specify a linger-on-close timeout.
      static int SO_OOBINLINE
      When the OOBINLINE option is set, any TCP urgent data received on the socket will be received through the socket input stream.
      static int SO_RCVBUF
      Set a hint the size of the underlying buffers used by the platform for incoming network I/O.
      static int SO_REUSEADDR
      Sets SO_REUSEADDR for a socket.
      static int SO_SNDBUF
      Set a hint the size of the underlying buffers used by the platform for outgoing network I/O.
      static int SO_TIMEOUT
      Set a timeout on blocking Socket operations:
      static int TCP_NODELAY
      Disable Nagle's algorithm for this connection.
    • Field Detail

      • SO_BINDADDR

        @Native
        static final int 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

        See Also:
        Socket.getLocalAddress(), DatagramSocket.getLocalAddress(), Constant Field Values
      • SO_REUSEADDR

        @Native
        static final int 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

        See Also:
        Constant Field Values
      • SO_BROADCAST

        @Native
        static final int 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.
        Since:
        1.4
        See Also:
        Constant Field Values
      • IP_MULTICAST_LOOP

        @Native
        static final int IP_MULTICAST_LOOP
        This option enables or disables local loopback of multicast datagrams. This option is enabled by default for Multicast Sockets.
        Since:
        1.4
        See Also:
        Constant Field Values
      • IP_TOS

        @Native
        static final int IP_TOS
        This option sets the type-of-service or traffic class field in the IP header for a TCP or UDP socket.
        Since:
        1.4
        See Also:
        Constant Field Values
      • SO_LINGER

        @Native
        static final int 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

        See Also:
        Socket.setSoLinger(boolean, int), Socket.getSoLinger(), Constant Field Values
      • SO_TIMEOUT

        @Native
        static final int SO_TIMEOUT
        Set a timeout on blocking Socket operations:
         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

        See Also:
        Socket.setSoTimeout(int), ServerSocket.setSoTimeout(int), DatagramSocket.setSoTimeout(int), Constant Field Values
      • SO_KEEPALIVE

        @Native
        static final int 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
        See Also:
        Socket.setKeepAlive(boolean), Socket.getKeepAlive(), Constant Field Values
    • Method Detail

      • setOption

        void setOption(int optID,
                       Object value)
                throws SocketException
        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, new Integer(10));
            // OK - set SO_LINGER w/ timeout of 10 sec.
         s.setOption(SO_LINGER, new Double(10));
            // ERROR - expects java.lang.Integer
        
        If the requested option is binary, it can be set using this method by a java.lang.Boolean:
         s.setOption(TCP_NODELAY, new Boolean(true));
            // OK - enables TCP_NODELAY, a binary option
         

        Any option can be disabled using this method with a Boolean(false):
         s.setOption(TCP_NODELAY, new Boolean(false));
            // OK - disables TCP_NODELAY
         s.setOption(SO_LINGER, new 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
        Parameters:
        optID - identifies the option
        value - the parameter of the socket option
        Throws:
        SocketException - if the option is unrecognized, the socket is closed, or some low-level error occurred
        See Also:
        getOption(int)
      • getOption

        Object getOption(int optID)
                  throws SocketException
        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);
         }
         
        Parameters:
        optID - an int identifying the option to fetch
        Returns:
        the value of the option
        Throws:
        SocketException - if the socket is closed
        SocketException - if optID is unknown along the protocol stack (including the SocketImpl)
        See Also:
        setOption(int, java.lang.Object)


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