java.net

## Class Socket

- java.lang.Object
- - java.net.Socket

- Direct Known Subclasses:
    SSLSocket

      public class Socket
      extends Object

  This class implements client sockets (also called just "sockets"). A socket is an endpoint for communication between two machines.

  The actual work of the socket is performed by an instance of the `SocketImpl` class. An application, by changing the socket factory that creates the socket implementation, can configure itself to create sockets appropriate to the local firewall.

  Since:
    JDK1.0
  See Also:
    `setSocketImplFactory(java.net.SocketImplFactory)`, `SocketImpl`, `SocketChannel`

- - ### Constructor Summary

    Constructors
    Modifier | Constructor and Description
    --- | ---
    `` | `Socket()` Creates an unconnected socket, with the system-default type of SocketImpl.
    `` | `Socket(InetAddress address, int port)` Creates a stream socket and connects it to the specified port number at the specified IP address.
    `` | `Socket(InetAddress host, int port, boolean stream)` Deprecated. Use DatagramSocket instead for UDP transport.
    `` | `Socket(InetAddress address, int port, InetAddress localAddr, int localPort)` Creates a socket and connects it to the specified remote address on the specified remote port.
    `` | `Socket(Proxy proxy)` Creates an unconnected socket, specifying the type of proxy, if any, that should be used regardless of any other settings.
    `protected` | `Socket(SocketImpl impl)` Creates an unconnected Socket with a user-specified SocketImpl.
    `` | `Socket(String host, int port)` Creates a stream socket and connects it to the specified port number on the named host.
    `` | `Socket(String host, int port, boolean stream)` Deprecated. Use DatagramSocket instead for UDP transport.
    `` | `Socket(String host, int port, InetAddress localAddr, int localPort)` Creates a socket and connects it to the specified remote host on the specified remote port.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `bind(SocketAddress bindpoint)` Binds the socket to a local address.
    `void` | `close()` Closes this socket.
    `void` | `connect(SocketAddress endpoint)` Connects this socket to the server.
    `void` | `connect(SocketAddress endpoint, int timeout)` Connects this socket to the server with a specified timeout value.
    `SocketChannel` | `getChannel()` Returns the unique `SocketChannel` object associated with this socket, if any.
    `InetAddress` | `getInetAddress()` Returns the address to which the socket is connected.
    `InputStream` | `getInputStream()` Returns an input stream for this socket.
    `boolean` | `getKeepAlive()` Tests if SO_KEEPALIVE is enabled.
    `InetAddress` | `getLocalAddress()` Gets the local address to which the socket is bound.
    `int` | `getLocalPort()` Returns the local port number to which this socket is bound.
    `SocketAddress` | `getLocalSocketAddress()` Returns the address of the endpoint this socket is bound to, or `null` if it is not bound yet.
    `boolean` | `getOOBInline()` Tests if OOBINLINE is enabled.
    `OutputStream` | `getOutputStream()` Returns an output stream for this socket.
    `int` | `getPort()` Returns the remote port number to which this socket is connected.
    `int` | `getReceiveBufferSize()` Gets the value of the SO_RCVBUF option for this `Socket`, that is the buffer size used by the platform for input on this `Socket`.
    `SocketAddress` | `getRemoteSocketAddress()` Returns the address of the endpoint this socket is connected to, or `null` if it is unconnected.
    `boolean` | `getReuseAddress()` Tests if SO_REUSEADDR is enabled.
    `int` | `getSendBufferSize()` Get value of the SO_SNDBUF option for this `Socket`, that is the buffer size used by the platform for output on this `Socket`.
    `int` | `getSoLinger()` Returns setting for SO_LINGER.
    `int` | `getSoTimeout()` Returns setting for SO_TIMEOUT.
    `boolean` | `getTcpNoDelay()` Tests if TCP_NODELAY is enabled.
    `int` | `getTrafficClass()` Gets traffic class or type-of-service in the IP header for packets sent from this Socket
    `boolean` | `isBound()` Returns the binding state of the socket.
    `boolean` | `isClosed()` Returns the closed state of the socket.
    `boolean` | `isConnected()` Returns the connection state of the socket.
    `boolean` | `isInputShutdown()` Returns whether the read-half of the socket connection is closed.
    `boolean` | `isOutputShutdown()` Returns whether the write-half of the socket connection is closed.
    `void` | `sendUrgentData(int data)` Send one byte of urgent data on the socket.
    `void` | `setKeepAlive(boolean on)` Enable/disable SO_KEEPALIVE.
    `void` | `setOOBInline(boolean on)` Enable/disable OOBINLINE (receipt of TCP urgent data) By default, this option is disabled and TCP urgent data received on a socket is silently discarded.
    `void` | `setPerformancePreferences(int connectionTime, int latency, int bandwidth)` Sets performance preferences for this socket.
    `void` | `setReceiveBufferSize(int size)` Sets the SO_RCVBUF option to the specified value for this `Socket`.
    `void` | `setReuseAddress(boolean on)` Enable/disable the SO_REUSEADDR socket option.
    `void` | `setSendBufferSize(int size)` Sets the SO_SNDBUF option to the specified value for this `Socket`.
    `static void` | `setSocketImplFactory(SocketImplFactory fac)` Sets the client socket implementation factory for the application.
    `void` | `setSoLinger(boolean on, int linger)` Enable/disable SO_LINGER with the specified linger time in seconds.
    `void` | `setSoTimeout(int timeout)` Enable/disable SO_TIMEOUT with the specified timeout, in milliseconds.
    `void` | `setTcpNoDelay(boolean on)` Enable/disable TCP_NODELAY (disable/enable Nagle's algorithm).
    `void` | `setTrafficClass(int tc)` Sets traffic class or type-of-service octet in the IP header for packets sent from this Socket.
    `void` | `shutdownInput()` Places the input stream for this socket at "end of stream".
    `void` | `shutdownOutput()` Disables the output stream for this socket.
    `String` | `toString()` Converts this socket to a `String`.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

- - ### Constructor Detail

    - #### Socket

          public Socket()

      Creates an unconnected socket, with the system-default type of SocketImpl.
      Since:
        JDK1.1

    - #### Socket

          public Socket(Proxy proxy)

      Creates an unconnected socket, specifying the type of proxy, if any, that should be used regardless of any other settings.

      If there is a security manager, its `checkConnect` method is called with the proxy host address and port number as its arguments. This could result in a SecurityException.

      Examples:

      - `Socket s = new Socket(Proxy.NO_PROXY);` will create a plain socket ignoring any other proxy configuration.
      - `Socket s = new Socket(new Proxy(Proxy.Type.SOCKS, new InetSocketAddress("socks.mydom.com", 1080)));` will create a socket connecting through the specified SOCKS proxy server.
      Parameters:
        `proxy` - a `Proxy` object specifying what kind of proxying should be used.
      Throws:
        `IllegalArgumentException` - if the proxy is of an invalid type or `null`.
        `SecurityException` - if a security manager is present and permission to connect to the proxy is denied.
      Since:
        1.5
      See Also:
        `ProxySelector`, `Proxy`

    - #### Socket

          protected Socket(SocketImpl impl)
                    throws SocketException

      Creates an unconnected Socket with a user-specified SocketImpl.

      Parameters:
        `impl` - an instance of a SocketImpl the subclass wishes to use on the Socket.
      Throws:
        `SocketException` - if there is an error in the underlying protocol, such as a TCP error.
      Since:
        JDK1.1

    - #### Socket

          public Socket(String host,
                int port)
                 throws UnknownHostException,
                        IOException

      Creates a stream socket and connects it to the specified port number on the named host.

      If the specified host is `null` it is the equivalent of specifying the address as ``InetAddress.getByName`(null)`. In other words, it is equivalent to specifying an address of the loopback interface.

      If the application has specified a server socket factory, that factory's `createSocketImpl` method is called to create the actual socket implementation. Otherwise a "plain" socket is created.

      If there is a security manager, its `checkConnect` method is called with the host address and `port` as its arguments. This could result in a SecurityException.

      Parameters:
        `host` - the host name, or `null` for the loopback address.
        `port` - the port number.
      Throws:
        `UnknownHostException` - if the IP address of the host could not be determined.
        `IOException` - if an I/O error occurs when creating the socket.
        `SecurityException` - if a security manager exists and its `checkConnect` method doesn't allow the operation.
      See Also:
        `setSocketImplFactory(java.net.SocketImplFactory)`, `SocketImpl`, `SocketImplFactory.createSocketImpl()`, `SecurityManager.checkConnect(java.lang.String, int)`

    - #### Socket

          public Socket(InetAddress address,
                int port)
                 throws IOException

      Creates a stream socket and connects it to the specified port number at the specified IP address.

      If the application has specified a socket factory, that factory's `createSocketImpl` method is called to create the actual socket implementation. Otherwise a "plain" socket is created.

      If there is a security manager, its `checkConnect` method is called with the host address and `port` as its arguments. This could result in a SecurityException.

      Parameters:
        `address` - the IP address.
        `port` - the port number.
      Throws:
        `IOException` - if an I/O error occurs when creating the socket.
        `SecurityException` - if a security manager exists and its `checkConnect` method doesn't allow the operation.
      See Also:
        `setSocketImplFactory(java.net.SocketImplFactory)`, `SocketImpl`, `SocketImplFactory.createSocketImpl()`, `SecurityManager.checkConnect(java.lang.String, int)`

    - #### Socket

          public Socket(String host,
                int port,
                InetAddress localAddr,
                int localPort)
                 throws IOException

      Creates a socket and connects it to the specified remote host on the specified remote port. The Socket will also bind() to the local address and port supplied.

      If the specified host is `null` it is the equivalent of specifying the address as ``InetAddress.getByName`(null)`. In other words, it is equivalent to specifying an address of the loopback interface.

      If there is a security manager, its `checkConnect` method is called with the host address and `port` as its arguments. This could result in a SecurityException.

      Parameters:
        `host` - the name of the remote host, or `null` for the loopback address.
        `port` - the remote port
        `localAddr` - the local address the socket is bound to
        `localPort` - the local port the socket is bound to
      Throws:
        `IOException` - if an I/O error occurs when creating the socket.
        `SecurityException` - if a security manager exists and its `checkConnect` method doesn't allow the operation.
      Since:
        JDK1.1
      See Also:
        `SecurityManager.checkConnect(java.lang.String, int)`

    - #### Socket

          public Socket(InetAddress address,
                int port,
                InetAddress localAddr,
                int localPort)
                 throws IOException

      Creates a socket and connects it to the specified remote address on the specified remote port. The Socket will also bind() to the local address and port supplied.

      If there is a security manager, its `checkConnect` method is called with the host address and `port` as its arguments. This could result in a SecurityException.

      Parameters:
        `address` - the remote address
        `port` - the remote port
        `localAddr` - the local address the socket is bound to
        `localPort` - the local port the socket is bound to
      Throws:
        `IOException` - if an I/O error occurs when creating the socket.
        `SecurityException` - if a security manager exists and its `checkConnect` method doesn't allow the operation.
      Since:
        JDK1.1
      See Also:
        `SecurityManager.checkConnect(java.lang.String, int)`

    - #### Socket

          @Deprecated
          public Socket(String host,
                           int port,
                           boolean stream)
                 throws IOException

      Deprecated. Use DatagramSocket instead for UDP transport.
      Creates a stream socket and connects it to the specified port number on the named host.

      If the specified host is `null` it is the equivalent of specifying the address as ``InetAddress.getByName`(null)`. In other words, it is equivalent to specifying an address of the loopback interface.

      If the stream argument is `true`, this creates a stream socket. If the stream argument is `false`, it creates a datagram socket.

      If the application has specified a server socket factory, that factory's `createSocketImpl` method is called to create the actual socket implementation. Otherwise a "plain" socket is created.

      If there is a security manager, its `checkConnect` method is called with the host address and `port` as its arguments. This could result in a SecurityException.

      If a UDP socket is used, TCP/IP related socket options will not apply.

      Parameters:
        `host` - the host name, or `null` for the loopback address.
        `port` - the port number.
        `stream` - a `boolean` indicating whether this is a stream socket or a datagram socket.
      Throws:
        `IOException` - if an I/O error occurs when creating the socket.
        `SecurityException` - if a security manager exists and its `checkConnect` method doesn't allow the operation.
      See Also:
        `setSocketImplFactory(java.net.SocketImplFactory)`, `SocketImpl`, `SocketImplFactory.createSocketImpl()`, `SecurityManager.checkConnect(java.lang.String, int)`

    - #### Socket

          @Deprecated
          public Socket(InetAddress host,
                           int port,
                           boolean stream)
                 throws IOException

      Deprecated. Use DatagramSocket instead for UDP transport.
      Creates a socket and connects it to the specified port number at the specified IP address.

      If the stream argument is `true`, this creates a stream socket. If the stream argument is `false`, it creates a datagram socket.

      If the application has specified a server socket factory, that factory's `createSocketImpl` method is called to create the actual socket implementation. Otherwise a "plain" socket is created.

      If there is a security manager, its `checkConnect` method is called with `host.getHostAddress()` and `port` as its arguments. This could result in a SecurityException.

      If UDP socket is used, TCP/IP related socket options will not apply.

      Parameters:
        `host` - the IP address.
        `port` - the port number.
        `stream` - if `true`, create a stream socket; otherwise, create a datagram socket.
      Throws:
        `IOException` - if an I/O error occurs when creating the socket.
        `SecurityException` - if a security manager exists and its `checkConnect` method doesn't allow the operation.
      See Also:
        `setSocketImplFactory(java.net.SocketImplFactory)`, `SocketImpl`, `SocketImplFactory.createSocketImpl()`, `SecurityManager.checkConnect(java.lang.String, int)`

  - ### Method Detail

    - #### connect

          public void connect(SocketAddress endpoint)
                       throws IOException

      Connects this socket to the server.
      Parameters:
        `endpoint` - the `SocketAddress`
      Throws:
        `IOException` - if an error occurs during the connection
        `IllegalBlockingModeException` - if this socket has an associated channel, and the channel is in non-blocking mode
        `IllegalArgumentException` - if endpoint is null or is a SocketAddress subclass not supported by this socket
      Since:
        1.4

    - #### connect

          public void connect(SocketAddress endpoint,
                     int timeout)
                       throws IOException

      Connects this socket to the server with a specified timeout value. A timeout of zero is interpreted as an infinite timeout. The connection will then block until established or an error occurs.
      Parameters:
        `endpoint` - the `SocketAddress`
        `timeout` - the timeout value to be used in milliseconds.
      Throws:
        `IOException` - if an error occurs during the connection
        `SocketTimeoutException` - if timeout expires before connecting
        `IllegalBlockingModeException` - if this socket has an associated channel, and the channel is in non-blocking mode
        `IllegalArgumentException` - if endpoint is null or is a SocketAddress subclass not supported by this socket
      Since:
        1.4

    - #### bind

          public void bind(SocketAddress bindpoint)
                    throws IOException

      Binds the socket to a local address.

      If the address is `null`, then the system will pick up an ephemeral port and a valid local address to bind the socket.

      Parameters:
        `bindpoint` - the `SocketAddress` to bind to
      Throws:
        `IOException` - if the bind operation fails, or if the socket is already bound.
        `IllegalArgumentException` - if bindpoint is a SocketAddress subclass not supported by this socket
      Since:
        1.4
      See Also:
        `isBound()`

    - #### getInetAddress

          public InetAddress getInetAddress()

      Returns the address to which the socket is connected.
      Returns:
        the remote IP address to which this socket is connected, or `null` if the socket is not connected.

    - #### getLocalAddress

          public InetAddress getLocalAddress()

      Gets the local address to which the socket is bound.
      Returns:
        the local address to which the socket is bound or `InetAddress.anyLocalAddress()` if the socket is not bound yet.
      Since:
        JDK1.1

    - #### getPort

          public int getPort()

      Returns the remote port number to which this socket is connected.
      Returns:
        the remote port number to which this socket is connected, or 0 if the socket is not connected yet.

    - #### getLocalPort

          public int getLocalPort()

      Returns the local port number to which this socket is bound.
      Returns:
        the local port number to which this socket is bound or -1 if the socket is not bound yet.

    - #### getRemoteSocketAddress

          public SocketAddress getRemoteSocketAddress()

      Returns the address of the endpoint this socket is connected to, or `null` if it is unconnected.
      Returns:
        a `SocketAddress` reprensenting the remote endpoint of this socket, or `null` if it is not connected yet.
      Since:
        1.4
      See Also:
        `getInetAddress()`, `getPort()`, `connect(SocketAddress, int)`, `connect(SocketAddress)`

    - #### getLocalSocketAddress

          public SocketAddress getLocalSocketAddress()

      Returns the address of the endpoint this socket is bound to, or `null` if it is not bound yet.
      Returns:
        a `SocketAddress` representing the local endpoint of this socket, or `null` if it is not bound yet.
      Since:
        1.4
      See Also:
        `getLocalAddress()`, `getLocalPort()`, `bind(SocketAddress)`

    - #### getChannel

          public SocketChannel getChannel()

      Returns the unique `SocketChannel` object associated with this socket, if any.

      A socket will have a channel if, and only if, the channel itself was created via the `SocketChannel.open` or `ServerSocketChannel.accept` methods.

      Returns:
        the socket channel associated with this socket, or `null` if this socket was not created for a channel
      Since:
        1.4

    - #### getInputStream

          public InputStream getInputStream()
                                     throws IOException

      Returns an input stream for this socket.

      If this socket has an associated channel then the resulting input stream delegates all of its operations to the channel. If the channel is in non-blocking mode then the input stream's `read` operations will throw an `IllegalBlockingModeException`.

      Under abnormal conditions the underlying connection may be broken by the remote host or the network software (for example a connection reset in the case of TCP connections). When a broken connection is detected by the network software the following applies to the returned input stream :-

      - The network software may discard bytes that are buffered by the socket. Bytes that aren't discarded by the network software can be read using `read`.

      - If there are no bytes buffered on the socket, or all buffered bytes have been consumed by `read`, then all subsequent calls to `read` will throw an `IOException`.

      - If there are no bytes buffered on the socket, and the socket has not been closed using `close`, then `available` will return `0`.

      Closing the returned `InputStream` will close the associated socket.

      Returns:
        an input stream for reading bytes from this socket.
      Throws:
        `IOException` - if an I/O error occurs when creating the input stream, the socket is closed, the socket is not connected, or the socket input has been shutdown using `shutdownInput()`

    - #### getOutputStream

          public OutputStream getOutputStream()
                                       throws IOException

      Returns an output stream for this socket.

      If this socket has an associated channel then the resulting output stream delegates all of its operations to the channel. If the channel is in non-blocking mode then the output stream's `write` operations will throw an `IllegalBlockingModeException`.

      Closing the returned `OutputStream` will close the associated socket.

      Returns:
        an output stream for writing bytes to this socket.
      Throws:
        `IOException` - if an I/O error occurs when creating the output stream or if the socket is not connected.

    - #### setTcpNoDelay

          public void setTcpNoDelay(boolean on)
                             throws SocketException

      Enable/disable TCP_NODELAY (disable/enable Nagle's algorithm).
      Parameters:
        `on` - `true` to enable TCP_NODELAY, `false` to disable.
      Throws:
        `SocketException` - if there is an error in the underlying protocol, such as a TCP error.
      Since:
        JDK1.1
      See Also:
        `getTcpNoDelay()`

    - #### getTcpNoDelay

          public boolean getTcpNoDelay()
                                throws SocketException

      Tests if TCP_NODELAY is enabled.
      Returns:
        a `boolean` indicating whether or not TCP_NODELAY is enabled.
      Throws:
        `SocketException` - if there is an error in the underlying protocol, such as a TCP error.
      Since:
        JDK1.1
      See Also:
        `setTcpNoDelay(boolean)`

    - #### setSoLinger

          public void setSoLinger(boolean on,
                         int linger)
                           throws SocketException

      Enable/disable SO_LINGER with the specified linger time in seconds. The maximum timeout value is platform specific. The setting only affects socket close.
      Parameters:
        `on` - whether or not to linger on.
        `linger` - how long to linger for, if on is true.
      Throws:
        `SocketException` - if there is an error in the underlying protocol, such as a TCP error.
        `IllegalArgumentException` - if the linger value is negative.
      Since:
        JDK1.1
      See Also:
        `getSoLinger()`

    - #### getSoLinger

          public int getSoLinger()
                          throws SocketException

      Returns setting for SO_LINGER. -1 returns implies that the option is disabled. The setting only affects socket close.
      Returns:
        the setting for SO_LINGER.
      Throws:
        `SocketException` - if there is an error in the underlying protocol, such as a TCP error.
      Since:
        JDK1.1
      See Also:
        `setSoLinger(boolean, int)`

    - #### sendUrgentData

          public void sendUrgentData(int data)
                              throws IOException

      Send one byte of urgent data on the socket. The byte to be sent is the lowest eight bits of the data parameter. The urgent byte is sent after any preceding writes to the socket OutputStream and before any future writes to the OutputStream.
      Parameters:
        `data` - The byte of data to send
      Throws:
        `IOException` - if there is an error sending the data.
      Since:
        1.4

    - #### setOOBInline

          public void setOOBInline(boolean on)
                            throws SocketException

      Enable/disable OOBINLINE (receipt of TCP urgent data) By default, this option is disabled and TCP urgent data received on a socket is silently discarded. If the user wishes to receive urgent data, then this option must be enabled. When enabled, urgent data is received inline with normal data.

      Note, only limited support is provided for handling incoming urgent data. In particular, no notification of incoming urgent data is provided and there is no capability to distinguish between normal data and urgent data unless provided by a higher level protocol.

      Parameters:
        `on` - `true` to enable OOBINLINE, `false` to disable.
      Throws:
        `SocketException` - if there is an error in the underlying protocol, such as a TCP error.
      Since:
        1.4
      See Also:
        `getOOBInline()`

    - #### getOOBInline

          public boolean getOOBInline()
                               throws SocketException

      Tests if OOBINLINE is enabled.
      Returns:
        a `boolean` indicating whether or not OOBINLINE is enabled.
      Throws:
        `SocketException` - if there is an error in the underlying protocol, such as a TCP error.
      Since:
        1.4
      See Also:
        `setOOBInline(boolean)`

    - #### setSoTimeout

          public void setSoTimeout(int timeout)
                            throws SocketException

      Enable/disable SO_TIMEOUT with the specified timeout, in milliseconds. With this option set to a non-zero timeout, a read() call on the InputStream associated with this Socket will block for only this amount of time. If the timeout expires, a java.net.SocketTimeoutException is raised, though the Socket is still valid. The option must be enabled prior to entering the blocking operation to have effect. The timeout must be > 0. A timeout of zero is interpreted as an infinite timeout.
      Parameters:
        `timeout` - the specified timeout, in milliseconds.
      Throws:
        `SocketException` - if there is an error in the underlying protocol, such as a TCP error.
      Since:
        JDK 1.1
      See Also:
        `getSoTimeout()`

    - #### getSoTimeout

          public int getSoTimeout()
                           throws SocketException

      Returns setting for SO_TIMEOUT. 0 returns implies that the option is disabled (i.e., timeout of infinity).
      Returns:
        the setting for SO_TIMEOUT
      Throws:
        `SocketException` - if there is an error in the underlying protocol, such as a TCP error.
      Since:
        JDK1.1
      See Also:
        `setSoTimeout(int)`

    - #### setSendBufferSize

          public void setSendBufferSize(int size)
                                 throws SocketException

      Sets the SO_SNDBUF option to the specified value for this `Socket`. The SO_SNDBUF option is used by the platform's networking code as a hint for the size to set the underlying network I/O buffers.

      Because SO_SNDBUF is a hint, applications that want to verify what size the buffers were set to should call `getSendBufferSize()`.

      Parameters:
        `size` - the size to which to set the send buffer size. This value must be greater than 0.
      Throws:
        `SocketException` - if there is an error in the underlying protocol, such as a TCP error.
        `IllegalArgumentException` - if the value is 0 or is negative.
      Since:
        1.2
      See Also:
        `getSendBufferSize()`

    - #### getSendBufferSize

          public int getSendBufferSize()
                                throws SocketException

      Get value of the SO_SNDBUF option for this `Socket`, that is the buffer size used by the platform for output on this `Socket`.
      Returns:
        the value of the SO_SNDBUF option for this `Socket`.
      Throws:
        `SocketException` - if there is an error in the underlying protocol, such as a TCP error.
      Since:
        1.2
      See Also:
        `setSendBufferSize(int)`

    - #### setReceiveBufferSize

          public void setReceiveBufferSize(int size)
                                    throws SocketException

      Sets the SO_RCVBUF option to the specified value for this `Socket`. The SO_RCVBUF option is used by the platform's networking code as a hint for the size to set the underlying network I/O buffers.

      Increasing the receive buffer size can increase the performance of network I/O for high-volume connection, while decreasing it can help reduce the backlog of incoming data.

      Because SO_RCVBUF is a hint, applications that want to verify what size the buffers were set to should call `getReceiveBufferSize()`.

      The value of SO_RCVBUF is also used to set the TCP receive window that is advertized to the remote peer. Generally, the window size can be modified at any time when a socket is connected. However, if a receive window larger than 64K is required then this must be requested before the socket is connected to the remote peer. There are two cases to be aware of:

      1. For sockets accepted from a ServerSocket, this must be done by calling `ServerSocket.setReceiveBufferSize(int)` before the ServerSocket is bound to a local address.

      2. For client sockets, setReceiveBufferSize() must be called before connecting the socket to its remote peer.

      Parameters:
        `size` - the size to which to set the receive buffer size. This value must be greater than 0.
      Throws:
        `IllegalArgumentException` - if the value is 0 or is negative.
        `SocketException` - if there is an error in the underlying protocol, such as a TCP error.
      Since:
        1.2
      See Also:
        `getReceiveBufferSize()`, `ServerSocket.setReceiveBufferSize(int)`

    - #### getReceiveBufferSize

          public int getReceiveBufferSize()
                                   throws SocketException

      Gets the value of the SO_RCVBUF option for this `Socket`, that is the buffer size used by the platform for input on this `Socket`.
      Returns:
        the value of the SO_RCVBUF option for this `Socket`.
      Throws:
        `SocketException` - if there is an error in the underlying protocol, such as a TCP error.
      Since:
        1.2
      See Also:
        `setReceiveBufferSize(int)`

    - #### setKeepAlive

          public void setKeepAlive(boolean on)
                            throws SocketException

      Enable/disable SO_KEEPALIVE.
      Parameters:
        `on` - whether or not to have socket keep alive turned on.
      Throws:
        `SocketException` - if there is an error in the underlying protocol, such as a TCP error.
      Since:
        1.3
      See Also:
        `getKeepAlive()`

    - #### getKeepAlive

          public boolean getKeepAlive()
                               throws SocketException

      Tests if SO_KEEPALIVE is enabled.
      Returns:
        a `boolean` indicating whether or not SO_KEEPALIVE is enabled.
      Throws:
        `SocketException` - if there is an error in the underlying protocol, such as a TCP error.
      Since:
        1.3
      See Also:
        `setKeepAlive(boolean)`

    - #### setTrafficClass

          public void setTrafficClass(int tc)
                               throws SocketException

      Sets traffic class or type-of-service octet in the IP header for packets sent from this Socket. As the underlying network implementation may ignore this value applications should consider it a hint.

      The tc must be in the range `0 <= tc <= 255` or an IllegalArgumentException will be thrown.

      Notes:

      For Internet Protocol v4 the value consists of an octet with precedence and TOS fields as detailed in RFC 1349. The TOS field is bitset created by bitwise-or'ing values such the following :-

      - `IPTOS_LOWCOST (0x02)`
      - `IPTOS_RELIABILITY (0x04)`
      - `IPTOS_THROUGHPUT (0x08)`
      - `IPTOS_LOWDELAY (0x10)`
      The last low order bit is always ignored as this corresponds to the MBZ (must be zero) bit.

      Setting bits in the precedence field may result in a SocketException indicating that the operation is not permitted.

      As RFC 1122 section 4.2.4.2 indicates, a compliant TCP implementation should, but is not required to, let application change the TOS field during the lifetime of a connection. So whether the type-of-service field can be changed after the TCP connection has been established depends on the implementation in the underlying platform. Applications should not assume that they can change the TOS field after the connection.

      For Internet Protocol v6 `tc` is the value that would be placed into the sin6_flowinfo field of the IP header.

      Parameters:
        `tc` - an `int` value for the bitset.
      Throws:
        `SocketException` - if there is an error setting the traffic class or type-of-service
      Since:
        1.4
      See Also:
        `getTrafficClass()`

    - #### getTrafficClass

          public int getTrafficClass()
                              throws SocketException

      Gets traffic class or type-of-service in the IP header for packets sent from this Socket

      As the underlying network implementation may ignore the traffic class or type-of-service set using `setTrafficClass(int)` this method may return a different value than was previously set using the `setTrafficClass(int)` method on this Socket.

      Returns:
        the traffic class or type-of-service already set
      Throws:
        `SocketException` - if there is an error obtaining the traffic class or type-of-service value.
      Since:
        1.4
      See Also:
        `setTrafficClass(int)`

    - #### setReuseAddress

          public void setReuseAddress(boolean on)
                               throws SocketException

      Enable/disable the SO_REUSEADDR socket option.

      When a TCP connection is closed the connection may remain in a timeout state for a period of time after the connection is closed (typically known as the `TIME_WAIT` state or `2MSL` wait state). For applications using a well known socket address or port it may not be possible to bind a socket to the required `SocketAddress` if there is a connection in the timeout state involving the socket address or port.

      Enabling `SO_REUSEADDR` prior to binding the socket using `bind(SocketAddress)` allows the socket to be bound even though a previous connection is in a timeout state.

      When a `Socket` is created the initial setting of `SO_REUSEADDR` is disabled.

      The behaviour when `SO_REUSEADDR` is enabled or disabled after a socket is bound (See `isBound()`) is not defined.

      Parameters:
        `on` - whether to enable or disable the socket option
      Throws:
        `SocketException` - if an error occurs enabling or disabling the `SO_RESUEADDR` socket option, or the socket is closed.
      Since:
        1.4
      See Also:
        `getReuseAddress()`, `bind(SocketAddress)`, `isClosed()`, `isBound()`

    - #### getReuseAddress

          public boolean getReuseAddress()
                                  throws SocketException

      Tests if SO_REUSEADDR is enabled.
      Returns:
        a `boolean` indicating whether or not SO_REUSEADDR is enabled.
      Throws:
        `SocketException` - if there is an error in the underlying protocol, such as a TCP error.
      Since:
        1.4
      See Also:
        `setReuseAddress(boolean)`

    - #### close

          public void close()
                     throws IOException

      Closes this socket.

      Any thread currently blocked in an I/O operation upon this socket will throw a `SocketException`.

      Once a socket has been closed, it is not available for further networking use (i.e. can't be reconnected or rebound). A new socket needs to be created.

      Closing this socket will also close the socket's `InputStream` and `OutputStream`.

      If this socket has an associated channel then the channel is closed as well.

      Throws:
        `IOException` - if an I/O error occurs when closing this socket.
      See Also:
        `isClosed()`

    - #### shutdownInput

          public void shutdownInput()
                             throws IOException

      Places the input stream for this socket at "end of stream". Any data sent to the input stream side of the socket is acknowledged and then silently discarded.

      If you read from a socket input stream after invoking shutdownInput() on the socket, the stream will return EOF.

      Throws:
        `IOException` - if an I/O error occurs when shutting down this socket.
      Since:
        1.3
      See Also:
        `shutdownOutput()`, `close()`, `setSoLinger(boolean, int)`, `isInputShutdown()`

    - #### shutdownOutput

          public void shutdownOutput()
                              throws IOException

      Disables the output stream for this socket. For a TCP socket, any previously written data will be sent followed by TCP's normal connection termination sequence. If you write to a socket output stream after invoking shutdownOutput() on the socket, the stream will throw an IOException.
      Throws:
        `IOException` - if an I/O error occurs when shutting down this socket.
      Since:
        1.3
      See Also:
        `shutdownInput()`, `close()`, `setSoLinger(boolean, int)`, `isOutputShutdown()`

    - #### toString

          public String toString()

      Converts this socket to a `String`.
      Overrides:
        `toString` in class `Object`
      Returns:
        a string representation of this socket.

    - #### isConnected

          public boolean isConnected()

      Returns the connection state of the socket.
      Returns:
        true if the socket successfuly connected to a server
      Since:
        1.4

    - #### isBound

          public boolean isBound()

      Returns the binding state of the socket.
      Returns:
        true if the socket successfuly bound to an address
      Since:
        1.4
      See Also:
        `bind(java.net.SocketAddress)`

    - #### isClosed

          public boolean isClosed()

      Returns the closed state of the socket.
      Returns:
        true if the socket has been closed
      Since:
        1.4
      See Also:
        `close()`

    - #### isInputShutdown

          public boolean isInputShutdown()

      Returns whether the read-half of the socket connection is closed.
      Returns:
        true if the input of the socket has been shutdown
      Since:
        1.4
      See Also:
        `shutdownInput()`

    - #### isOutputShutdown

          public boolean isOutputShutdown()

      Returns whether the write-half of the socket connection is closed.
      Returns:
        true if the output of the socket has been shutdown
      Since:
        1.4
      See Also:
        `shutdownOutput()`

    - #### setSocketImplFactory

          public static void setSocketImplFactory(SocketImplFactory fac)
                                           throws IOException

      Sets the client socket implementation factory for the application. The factory can be specified only once.

      When an application creates a new client socket, the socket implementation factory's `createSocketImpl` method is called to create the actual socket implementation.

      Passing `null` to the method is a no-op unless the factory was already set.

      If there is a security manager, this method first calls the security manager's `checkSetFactory` method to ensure the operation is allowed. This could result in a SecurityException.

      Parameters:
        `fac` - the desired factory.
      Throws:
        `IOException` - if an I/O error occurs when setting the socket factory.
        `SocketException` - if the factory is already defined.
        `SecurityException` - if a security manager exists and its `checkSetFactory` method doesn't allow the operation.
      See Also:
        `SocketImplFactory.createSocketImpl()`, `SecurityManager.checkSetFactory()`

    - #### setPerformancePreferences

          public void setPerformancePreferences(int connectionTime,
                                       int latency,
                                       int bandwidth)

      Sets performance preferences for this socket.

      Sockets use the TCP/IP protocol by default. Some implementations may offer alternative protocols which have different performance characteristics than TCP/IP. This method allows the application to express its own preferences as to how these tradeoffs should be made when the implementation chooses from the available protocols.

      Performance preferences are described by three integers whose values indicate the relative importance of short connection time, low latency, and high bandwidth. The absolute values of the integers are irrelevant; in order to choose a protocol the values are simply compared, with larger values indicating stronger preferences. Negative values represent a lower priority than positive values. If the application prefers short connection time over both low latency and high bandwidth, for example, then it could invoke this method with the values `(1, 0, 0)`. If the application prefers high bandwidth above low latency, and low latency above short connection time, then it could invoke this method with the values `(0, 1, 2)`.

      Invoking this method after this socket has been connected will have no effect.

      Parameters:
        `connectionTime` - An `int` expressing the relative importance of a short connection time
        `latency` - An `int` expressing the relative importance of low latency
        `bandwidth` - An `int` expressing the relative importance of high bandwidth
      Since:
        1.5

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