Module java.base
Package java.net

# Class SocketImpl

java.lang.Object
java.net.SocketImpl

All Implemented Interfaces:
  `SocketOptions`

public abstract class SocketImpl extends Object implements SocketOptions
The abstract class `SocketImpl` is a common superclass of all classes that actually implement sockets. It is used to create both client and server sockets.

Implementation Note:
  Client and server sockets created with the `Socket` and `SocketServer` public constructors create a system-default `SocketImpl`. The JDK historically used a `SocketImpl` implementation type named "PlainSocketImpl" that has since been replaced by a newer implementation. The JDK continues to ship with the older implementation to allow code to run that depends on unspecified behavior that differs between the old and new implementations. The old implementation will be used if the Java virtual machine is started with the system property `jdk.net.usePlainSocketImpl` set to use the old implementation. It may also be set in the JDK's network configuration file, located in `${java.home}/conf/net.properties`. The value of the property is the string representation of a boolean. If set without a value then it defaults to `true`, hence running with `-Djdk.net.usePlainSocketImpl` or `-Djdk.net.usePlainSocketImpl=true` will configure the Java virtual machine to use the old implementation. The property and old implementation will be removed in a future version.
Since:
  1.0

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `protected InetAddress`
  `address`
  The IP address of the remote end of this socket.
  `protected FileDescriptor`
  `fd`
  The file descriptor object for this socket.
  `protected int`
  `localport`
  The local port number to which this socket is connected.
  `protected int`
  `port`
  The port number on the remote host to which this socket is connected.

  ### Fields declared in interface java.net.SocketOptions

  `IP_MULTICAST_IF, IP_MULTICAST_IF2, IP_MULTICAST_LOOP, IP_TOS, SO_BINDADDR, SO_BROADCAST, SO_KEEPALIVE, SO_LINGER, SO_OOBINLINE, SO_RCVBUF, SO_REUSEADDR, SO_REUSEPORT, SO_SNDBUF, SO_TIMEOUT, TCP_NODELAY`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `SocketImpl()`
  Initialize a new instance of this class

- ## Method Summary

  Modifier and Type
  Method
  Description
  `protected abstract void`
  `accept(SocketImpl s)`
  Accepts a connection.
  `protected abstract int`
  `available()`
  Returns the number of bytes that can be read from this socket without blocking.
  `protected abstract void`
  `bind(InetAddress host, int port)`
  Binds this socket to the specified local IP address and port number.
  `protected abstract void`
  `close()`
  Closes this socket.
  `protected abstract void`
  `connect(String host, int port)`
  Connects this socket to the specified port on the named host.
  `protected abstract void`
  `connect(InetAddress address, int port)`
  Connects this socket to the specified port number on the specified host.
  `protected abstract void`
  `connect(SocketAddress address, int timeout)`
  Connects this socket to the specified port number on the specified host.
  `protected abstract void`
  `create(boolean stream)`
  Creates either a stream or a datagram socket.
  `protected FileDescriptor`
  `getFileDescriptor()`
  Returns the value of this socket's `fd` field.
  `protected InetAddress`
  `getInetAddress()`
  Returns the value of this socket's `address` field.
  `protected abstract InputStream`
  `getInputStream()`
  Returns an input stream for this socket.
  `protected int`
  `getLocalPort()`
  Returns the value of this socket's `localport` field.
  `protected <T> T`
  `getOption(SocketOption<T> name)`
  Called to get a socket option.
  `protected abstract OutputStream`
  `getOutputStream()`
  Returns an output stream for this socket.
  `protected int`
  `getPort()`
  Returns the value of this socket's `port` field.
  `protected abstract void`
  `listen(int backlog)`
  Sets the maximum queue length for incoming connection indications (a request to connect) to the `count` argument.
  `protected abstract void`
  `sendUrgentData(int data)`
  Send one byte of urgent data on the socket.
  `protected <T> void`
  `setOption(SocketOption<T> name, T value)`
  Called to set a socket option.
  `protected void`
  `setPerformancePreferences(int connectionTime, int latency, int bandwidth)`
  Sets performance preferences for this socket.
  `protected void`
  `shutdownInput()`
  Places the input stream for this socket at "end of stream".
  `protected void`
  `shutdownOutput()`
  Disables the output stream for this socket.
  `protected Set<SocketOption<?>>`
  `supportedOptions()`
  Returns a set of SocketOptions supported by this impl and by this impl's socket (Socket or ServerSocket)
  `protected boolean`
  `supportsUrgentData()`
  Returns whether or not this SocketImpl supports sending urgent data.
  `String`
  `toString()`
  Returns the address and port of this socket as a `String`.

  ### Methods declared in class java.lang.Object

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

  ### Methods declared in interface java.net.SocketOptions

  `getOption, setOption`

- ## Field Details

  - ### fd

    protected FileDescriptor fd
    The file descriptor object for this socket.

  - ### address

    protected InetAddress address
    The IP address of the remote end of this socket.

  - ### port

    protected int port
    The port number on the remote host to which this socket is connected.

  - ### localport

    protected int localport
    The local port number to which this socket is connected.

- ## Constructor Details

  - ### SocketImpl

    public SocketImpl()
    Initialize a new instance of this class

- ## Method Details

  - ### create

    protected abstract void create(boolean stream) throws IOException
    Creates either a stream or a datagram socket.
    Parameters:
      `stream` - if `true`, create a stream socket; otherwise, create a datagram socket.
    Throws:
      `IOException` - if an I/O error occurs while creating the socket.

  - ### connect

    protected abstract void connect(String host, int port) throws IOException
    Connects this socket to the specified port on the named host.
    Parameters:
      `host` - the name of the remote host.
      `port` - the port number.
    Throws:
      `IOException` - if an I/O error occurs when connecting to the remote host.

  - ### connect

    protected abstract void connect(InetAddress address, int port) throws IOException
    Connects this socket to the specified port number on the specified host.
    Parameters:
      `address` - the IP address of the remote host.
      `port` - the port number.
    Throws:
      `IOException` - if an I/O error occurs when attempting a connection.

  - ### connect

    protected abstract void connect(SocketAddress address, int timeout) throws IOException
    Connects this socket to the specified port number on the specified host. A timeout of zero is interpreted as an infinite timeout. The connection will then block until established or an error occurs.
    Parameters:
      `address` - the Socket address of the remote host.
      `timeout` - the timeout value, in milliseconds, or zero for no timeout.
    Throws:
      `IOException` - if an I/O error occurs when attempting a connection.
    Since:
      1.4

  - ### bind

    protected abstract void bind(InetAddress host, int port) throws IOException
    Binds this socket to the specified local IP address and port number.
    Parameters:
      `host` - an IP address that belongs to a local interface.
      `port` - the port number.
    Throws:
      `IOException` - if an I/O error occurs when binding this socket.

  - ### listen

    protected abstract void listen(int backlog) throws IOException
    Sets the maximum queue length for incoming connection indications (a request to connect) to the `count` argument. If a connection indication arrives when the queue is full, the connection is refused.
    Parameters:
      `backlog` - the maximum length of the queue.
    Throws:
      `IOException` - if an I/O error occurs when creating the queue.

  - ### accept

    protected abstract void accept(SocketImpl s) throws IOException
    Accepts a connection.
    Parameters:
      `s` - the accepted connection.
    Throws:
      `IOException` - if an I/O error occurs when accepting the connection.

  - ### getInputStream

    protected abstract InputStream getInputStream() throws IOException
    Returns an input stream for this socket.
    Returns:
      a stream for reading from this socket.
    Throws:
      `IOException` - if an I/O error occurs when creating the input stream.

  - ### getOutputStream

    protected abstract OutputStream getOutputStream() throws IOException
    Returns an output stream for this socket.
    Returns:
      an output stream for writing to this socket.
    Throws:
      `IOException` - if an I/O error occurs when creating the output stream.

  - ### available

    protected abstract int available() throws IOException
    Returns the number of bytes that can be read from this socket without blocking.
    Returns:
      the number of bytes that can be read from this socket without blocking.
    Throws:
      `IOException` - if an I/O error occurs when determining the number of bytes available.

  - ### close

    protected abstract void close() throws IOException
    Closes this socket.
    Throws:
      `IOException` - if an I/O error occurs when closing this socket.

  - ### shutdownInput

    protected void shutdownInput() throws IOException
    Places the input stream for this socket at "end of stream". Any data sent to this socket is acknowledged and then silently discarded. If you read from a socket input stream after invoking this method on the socket, the stream's `available` method will return 0, and its `read` methods will return `-1` (end of stream).
    Throws:
      `IOException` - if an I/O error occurs when shutting down this socket.
    Since:
      1.3
    See Also:
      - `Socket.shutdownOutput()`
      - `Socket.close()`
      - `Socket.setSoLinger(boolean, int)`

  - ### shutdownOutput

    protected 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:
      - `Socket.shutdownInput()`
      - `Socket.close()`
      - `Socket.setSoLinger(boolean, int)`

  - ### getFileDescriptor

    protected FileDescriptor getFileDescriptor()
    Returns the value of this socket's `fd` field.
    Returns:
      the value of this socket's `fd` field.
    See Also:
      - `fd`

  - ### getInetAddress

    protected InetAddress getInetAddress()
    Returns the value of this socket's `address` field.
    Returns:
      the value of this socket's `address` field.
    See Also:
      - `address`

  - ### getPort

    protected int getPort()
    Returns the value of this socket's `port` field.
    Returns:
      the value of this socket's `port` field.
    See Also:
      - `port`

  - ### supportsUrgentData

    protected boolean supportsUrgentData()
    Returns whether or not this SocketImpl supports sending urgent data. By default, false is returned unless the method is overridden in a sub-class
    Returns:
      true if urgent data supported
    Since:
      1.4
    See Also:
      - `address`

  - ### sendUrgentData

    protected abstract void sendUrgentData(int data) throws IOException
    Send one byte of urgent data on the socket. The byte to be sent is the low eight bits of the parameter
    Parameters:
      `data` - The byte of data to send
    Throws:
      `IOException` - if there is an error sending the data.
    Since:
      1.4

  - ### getLocalPort

    protected int getLocalPort()
    Returns the value of this socket's `localport` field.
    Returns:
      the value of this socket's `localport` field.
    See Also:
      - `localport`

  - ### toString

    public String toString()
    Returns the address and port of this socket as a `String`.
    Overrides:
      `toString` in class `Object`
    Returns:
      a string representation of this socket.

  - ### setPerformancePreferences

    protected 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)`. By default, this method does nothing, unless it is overridden in a sub-class.

    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

  - ### setOption

    protected <T> void setOption(SocketOption<T> name, T value) throws IOException
    Called to set a socket option.
    Implementation Requirements:
      The default implementation of this method first checks that the given socket option `name` is not null, then throws `UnsupportedOperationException`. Subclasses should override this method with an appropriate implementation.
    Type Parameters:
      `T` - The type of the socket option value
    Parameters:
      `name` - The socket option
      `value` - The value of the socket option. A value of `null` may be valid for some options.
    Throws:
      `UnsupportedOperationException` - if the SocketImpl does not support the option
      `IllegalArgumentException` - if the value is not valid for the option
      `IOException` - if an I/O error occurs, or if the socket is closed
      `NullPointerException` - if name is `null`
    Since:
      9

  - ### getOption

    protected <T> T getOption(SocketOption<T> name) throws IOException
    Called to get a socket option.
    Implementation Requirements:
      The default implementation of this method first checks that the given socket option `name` is not null, then throws `UnsupportedOperationException`. Subclasses should override this method with an appropriate implementation.
    Type Parameters:
      `T` - The type of the socket option value
    Parameters:
      `name` - The socket option
    Returns:
      the value of the named option
    Throws:
      `UnsupportedOperationException` - if the SocketImpl does not support the option
      `IOException` - if an I/O error occurs, or if the socket is closed
      `NullPointerException` - if name is `null`
    Since:
      9

  - ### supportedOptions

    protected Set<SocketOption<?>> supportedOptions()
    Returns a set of SocketOptions supported by this impl and by this impl's socket (Socket or ServerSocket)
    Implementation Requirements:
      The default implementation of this method returns an empty set. Subclasses should override this method with an appropriate implementation.
    Returns:
      a Set of SocketOptions
    Since:
      9