Creates an unconnected socket, with the system-default type of SocketImpl.

since	JDK1.1
revised	1.4

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.

proxy	a Proxy object specifying what kind of proxying should be used.
Throws	IllegalArgumentException: if the proxy is of an invalid type or null.
Throws	SecurityException: if a security manager is present and permission to connect to the proxy is denied.
since	1.5
See also	java.net.ProxySelector, java.net.Proxy

Creates an unconnected Socket with a user-specified SocketImpl.

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

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.

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.
Throws	IOException: if an I/O error occurs when creating the socket.
Throws	SecurityException: if a security manager exists and its checkConnect method doesn't allow the operation.
See also	setSocketImplFactory(java.net.SocketImplFactory), java.net.SocketImpl, createSocketImpl(), checkConnect

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.

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

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.

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.
Throws	SecurityException: if a security manager exists and its checkConnect method doesn't allow the operation.
since	JDK1.1
See also	checkConnect

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.

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.
Throws	SecurityException: if a security manager exists and its checkConnect method doesn't allow the operation.
since	JDK1.1
See also	checkConnect

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.

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.
Throws	SecurityException: if a security manager exists and its checkConnect method doesn't allow the operation.
deprecated	Use DatagramSocket instead for UDP transport.
See also	setSocketImplFactory(java.net.SocketImplFactory), java.net.SocketImpl, createSocketImpl(), checkConnect

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.

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.
Throws	SecurityException: if a security manager exists and its checkConnect method doesn't allow the operation.
deprecated	Use DatagramSocket instead for UDP transport.
See also	setSocketImplFactory(java.net.SocketImplFactory), java.net.SocketImpl, createSocketImpl(), checkConnect

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.

bindpoint	the SocketAddress to bind to
Throws	IOException: if the bind operation fails, or if the socket is already bound.
Throws	IllegalArgumentException: if bindpoint is a SocketAddress subclass not supported by this socket
since	1.4
See also	isBound

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.
revised	1.4
spec	JSR-51
See also	isClosed

Connects this socket to the server.

endpoint	the SocketAddress
Throws	IOException: if an error occurs during the connection
Throws	java.nio.channels.IllegalBlockingModeException: if this socket has an associated channel, and the channel is in non-blocking mode
Throws	IllegalArgumentException: if endpoint is null or is a SocketAddress subclass not supported by this socket
since	1.4
spec	JSR-51

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.

endpoint	the SocketAddress
timeout	the timeout value to be used in milliseconds.
Throws	IOException: if an error occurs during the connection
Throws	SocketTimeoutException: if timeout expires before connecting
Throws	java.nio.channels.IllegalBlockingModeException: if this socket has an associated channel, and the channel is in non-blocking mode
Throws	IllegalArgumentException: if endpoint is null or is a SocketAddress subclass not supported by this socket
since	1.4
spec	JSR-51

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.

data	The byte of data to send
Throws	IOException: if there is an error sending the data.
since	1.4

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

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

Converts this socket to a String.

return

a string representation of this socket.

Returns the binding state of the socket.

return	true if the socket successfuly bound to an address
since	1.4
See also	bind

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.

return	the socket channel associated with this socket, or null if this socket was not created for a channel
since	1.4
spec	JSR-51

Returns the closed state of the socket.

return	true if the socket has been closed
since	1.4
See also	close

Returns the connection state of the socket.

return	true if the socket successfuly connected to a server
since	1.4

Returns the address to which the socket is connected.

return

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

Returns whether the read-half of the socket connection is closed.

return	true if the input of the socket has been shutdown
since	1.4
See also	shutdownInput

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 java.nio.channels.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.

return	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()
revised	1.4
spec	JSR-51

Enable/disable SO_KEEPALIVE.

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()

Tests if SO_KEEPALIVE is enabled.

return	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)

Gets the local address to which the socket is bound.

return	the local address to which the socket is bound or InetAddress.anyLocalAddress() if the socket is not bound yet.
since	JDK1.1

Returns the local port to which this socket is bound.

return

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

Returns the address of the endpoint this socket is bound to, or null if it is not bound yet.

return	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)

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.

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()

Tests if OOBINLINE is enabled.

return	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)

Returns whether the write-half of the socket connection is closed.

return	true if the output of the socket has been shutdown
since	1.4
See also	shutdownOutput

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 java.nio.channels.IllegalBlockingModeException.

Closing the returned OutputStream will close the associated socket.

return	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.
revised	1.4
spec	JSR-51

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.

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

Returns the remote port to which this socket is connected.

return

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

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.

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.
Throws	SocketException: if there is an error in the underlying protocol, such as a TCP error.
since	1.2
See also	getReceiveBufferSize(), setReceiveBufferSize(int)

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.

return	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)

Returns the address of the endpoint this socket is connected to, or null if it is unconnected.

return	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)

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.

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()

Tests if SO_REUSEADDR is enabled.

return	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)

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().

Throws	SocketException: if there is an error in the underlying protocol, such as a TCP error.
size	the size to which to set the send buffer size. This value must be greater than 0.
Throws	IllegalArgumentException: if the value is 0 or is negative.
since	1.2
See also	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.

return	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)

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.

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

Enable/disable SO_LINGER with the specified linger time in seconds. The maximum timeout value is platform specific. The setting only affects socket close.

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.
Throws	IllegalArgumentException: if the linger value is negative.
since	JDK1.1
See also	getSoLinger()

Returns setting for SO_LINGER. -1 returns implies that the option is disabled. The setting only affects socket close.

return	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)

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.

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()

Returns setting for SO_TIMEOUT. 0 returns implies that the option is disabled (i.e., timeout of infinity).

return	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)

Enable/disable TCP_NODELAY (disable/enable Nagle's algorithm).

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()

Tests if TCP_NODELAY is enabled.

return	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)

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.

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

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.

return	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)