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## java.net
Class Socket

    java.lang.Object
      |
      +--java.net.Socket

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`

Constructor Summary
`protected` | `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 address, int port, InetAddress localAddr, int localPort)` Creates a socket and connects it to the specified remote address on the specified remote port.
`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, InetAddress localAddr, int localPort)` Creates a socket and connects it to the specified remote host on the specified remote port.

Method Summary
`void` | `close()` Closes this socket.
`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 to which this socket is bound.
`OutputStream` | `getOutputStream()` Returns an output stream for this socket.
`int` | `getPort()` Returns the remote port 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`.
`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.
`void` | `setKeepAlive(boolean on)` Enable/disable SO_KEEPALIVE.
`void` | `setReceiveBufferSize(int size)` Sets the SO_RCVBUF option to the specified value for this `Socket`.
`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` | `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

    protected Socket()

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

### 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 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.
    `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 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
    `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)`

Method Detail

### getInetAddress

    public InetAddress getInetAddress()

  Returns the address to which the socket is connected.
  Returns:
    the remote IP address to which this socket is 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.
  Since:
    JDK1.1

### getPort

    public int getPort()

  Returns the remote port to which this socket is connected.
  Returns:
    the remote port number to which this socket is connected.

### getLocalPort

    public int getLocalPort()

  Returns the local port to which this socket is bound.
  Returns:
    the local port number to which this socket is connected.

### getInputStream

    public InputStream getInputStream()
                               throws IOException

  Returns an input stream for this socket.
  Returns:
    an input stream for reading bytes from this socket.
  Throws:
    `IOException` - if an I/O error occurs when creating the input stream.

### getOutputStream

    public OutputStream getOutputStream()
                                 throws IOException

  Returns an output stream for this socket.
  Returns:
    an output stream for writing bytes to this socket.
  Throws:
    `IOException` - if an I/O error occurs when creating the output stream.

### 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 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)`

### 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.io.InterruptedIOException 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.

  Increasing 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. For UDP, this sets the maximum size of a packet that may be sent on this `Socket`.

  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.
  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.
  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 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. For UDP, this sets the maximum size of a packet that may be sent on this `Socket`.

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

  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.
  See Also:
    `getReceiveBufferSize()`

### 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.
  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)`

### close

    public void close()
               throws IOException

  Closes this socket.
  Throws:
    `IOException` - if an I/O error occurs when closing this socket.

### 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.
  See Also:
    `shutdownOutput()`, `close()`, `setSoLinger(boolean, int)`

### 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.
  See Also:
    `shutdownInput()`, `close()`, `setSoLinger(boolean, int)`

### toString

    public String toString()

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

### 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.

  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()`

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