Socket

public class Socket extends Object
implements Closeable

Known Direct Subclasses SSLSocket SSLSocket This class extends Sockets and provides secure socket using protocols such as the "Secure Sockets Layer" (SSL) or IETF "Transport Layer Security" (TLS) protocols.

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.

See Also

• setSocketImplFactory(java.net.SocketImplFactory)
• SocketImpl
• SocketChannel

Public Constructor Summary

	Socket() Creates an unconnected socket, with the system-default type of SocketImpl.
	Socket(Proxy proxy) Creates an unconnected socket, specifying the type of proxy, if any, that should be used regardless of any other settings.
	Socket(String host, int port) Creates a stream socket and connects it to the specified port number on the named host.
	Socket(InetAddress address, int port) Creates a stream socket and connects it to the specified port number at the specified IP address.
	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.
	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(String host, int port, boolean stream) This constructor is deprecated. Use DatagramSocket instead for UDP transport.
	Socket(InetAddress host, int port, boolean stream) This constructor is deprecated. Use DatagramSocket instead for UDP transport.

Protected Constructor Summary

Socket(SocketImpl impl) Creates an unconnected Socket with a user-specified SocketImpl.

Public Method Summary

void	bind(SocketAddress bindpoint) Binds the socket to a local address.
synchronized void	close() Closes this socket.
void	connect(SocketAddress endpoint, int timeout) Connects this socket to the server with a specified timeout value.
void	connect(SocketAddress endpoint) Connects this socket to the server.
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.
boolean	getOOBInline() Tests if SO_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.
synchronized 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.
synchronized 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.
synchronized 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 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.
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 SO_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.
synchronized 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.
synchronized void	setSendBufferSize(int size) Sets the SO_SNDBUF option to the specified value for this Socket.
void	setSoLinger(boolean on, int linger) Enable/disable SO_LINGER with the specified linger time in seconds.
synchronized void	setSoTimeout(int timeout) Enable/disable SO_TIMEOUT with the specified timeout, in milliseconds.
synchronized static void	setSocketImplFactory(SocketImplFactory fac) Sets the client socket implementation factory for the application.
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.

Inherited Method Summary

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

From interface java.io.Closeable

abstract void

close() Closes this stream and releases any system resources associated with it.

From interface java.lang.AutoCloseable

abstract void

close() Closes this resource, relinquishing any underlying resources.

Public Constructors

public Socket ()

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

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.

See Also

• ProxySelector
• Proxy

public Socket (String host, int port)

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.
IllegalArgumentException	if the port parameter is outside the specified range of valid port values, which is between 0 and 65535, inclusive.

See Also

• setSocketImplFactory(java.net.SocketImplFactory)
• SocketImpl
• SocketImplFactory.createSocketImpl()
• SecurityManager.checkConnect(String, int)

public Socket (InetAddress address, int port)

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.
IllegalArgumentException	if the port parameter is outside the specified range of valid port values, which is between 0 and 65535, inclusive.
NullPointerException	if address is null.

See Also

• setSocketImplFactory(java.net.SocketImplFactory)
• SocketImpl
• SocketImplFactory.createSocketImpl()
• SecurityManager.checkConnect(String, int)

public 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. 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.

A local port number of zero will let the system pick up a free port in the bind operation.

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, or null for the anyLocal address.
localPort	the local port the socket is bound to, or zero for a system selected free port.

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 connection to the destination, or if its checkListen method doesn't allow the bind to the local port.
IllegalArgumentException	if the port parameter or localPort parameter is outside the specified range of valid port values, which is between 0 and 65535, inclusive.

See Also

• SecurityManager.checkConnect(String, int)

public 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. The Socket will also bind() to the local address and port supplied.

If the specified local address is null it is the equivalent of specifying the address as the AnyLocal address (see InetAddress.isAnyLocalAddress()).

A local port number of zero will let the system pick up a free port in the bind operation.

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, or null for the anyLocal address.
localPort	the local port the socket is bound to or zero for a system selected free port.

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 connection to the destination, or if its checkListen method doesn't allow the bind to the local port.
IllegalArgumentException	if the port parameter or localPort parameter is outside the specified range of valid port values, which is between 0 and 65535, inclusive.
NullPointerException	if address is null.

See Also

• SecurityManager.checkConnect(String, int)

public Socket (String host, int port, boolean stream)

This constructor is 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.
IllegalArgumentException	if the port parameter is outside the specified range of valid port values, which is between 0 and 65535, inclusive.

See Also

• setSocketImplFactory(java.net.SocketImplFactory)
• SocketImpl
• SocketImplFactory.createSocketImpl()
• SecurityManager.checkConnect(String, int)

public Socket (InetAddress host, int port, boolean stream)

This constructor is 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.
IllegalArgumentException	if the port parameter is outside the specified range of valid port values, which is between 0 and 65535, inclusive.
NullPointerException	if host is null.

See Also

• setSocketImplFactory(java.net.SocketImplFactory)
• SocketImpl
• SocketImplFactory.createSocketImpl()
• SecurityManager.checkConnect(String, int)

Protected Constructors

protected Socket (SocketImpl impl)

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.

Public Methods

public void bind (SocketAddress bindpoint)

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
SecurityException	if a security manager exists and its checkListen method doesn't allow the bind to the local port.

See Also

• isBound()

public synchronized void close ()

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()

public void connect (SocketAddress endpoint, int timeout)

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

public void connect (SocketAddress endpoint)

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

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

public InetAddress getInetAddress ()

Returns the address to which the socket is connected.

If the socket was connected prior to being closed, then this method will continue to return the connected address after the socket is closed.

Returns

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

public InputStream getInputStream ()

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()

public boolean getKeepAlive ()

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.

See Also

• setKeepAlive(boolean)

public InetAddress getLocalAddress ()

Gets the local address to which the socket is bound.

If there is a security manager set, its checkConnect method is called with the local address and -1 as its arguments to see if the operation is allowed. If the operation is not allowed, the loopback address is returned.

Returns

• the local address to which the socket is bound, the loopback address if denied by the security manager, or the wildcard address if the socket is closed or not bound yet.

See Also

• SecurityManager.checkConnect(String, int)

public int getLocalPort ()

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

If the socket was bound prior to being closed, then this method will continue to return the local port number after the socket is closed.

Returns

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

public SocketAddress getLocalSocketAddress ()

Returns the address of the endpoint this socket is bound to.

If a socket bound to an endpoint represented by an InetSocketAddress is closed, then this method will continue to return an InetSocketAddress after the socket is closed. In that case the returned InetSocketAddress's address is the wildcard address and its port is the local port that it was bound to.

If there is a security manager set, its checkConnect method is called with the local address and -1 as its arguments to see if the operation is allowed. If the operation is not allowed, a SocketAddress representing the loopback address and the local port to which this socket is bound is returned.

Returns

• a SocketAddress representing the local endpoint of this socket, or a SocketAddress representing the loopback address if denied by the security manager, or null if the socket is not bound yet.

See Also

• getLocalAddress()
• getLocalPort()
• bind(SocketAddress)
• SecurityManager.checkConnect(String, int)

public boolean getOOBInline ()

Tests if SO_OOBINLINE is enabled.

Returns

• a boolean indicating whether or not SO_OOBINLINEis enabled.

Throws

SocketException	if there is an error in the underlying protocol, such as a TCP error.

See Also

• setOOBInline(boolean)

public OutputStream getOutputStream ()

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.

public int getPort ()

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

If the socket was connected prior to being closed, then this method will continue to return the connected port number after the socket is closed.

Returns

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

public synchronized 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.

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)

public SocketAddress getRemoteSocketAddress ()

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

If the socket was connected prior to being closed, then this method will continue to return the connected address after the socket is closed.

Returns

• a SocketAddress representing the remote endpoint of this socket, or null if it is not connected yet.

See Also

• getInetAddress()
• getPort()
• connect(SocketAddress, int)
• connect(SocketAddress)

public boolean getReuseAddress ()

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.

See Also

• setReuseAddress(boolean)

public synchronized 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.

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)

public int getSoLinger ()

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.

See Also

• setSoLinger(boolean, int)

public synchronized int getSoTimeout ()

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.

See Also

• setSoTimeout(int)

public boolean getTcpNoDelay ()

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.

See Also

• setTcpNoDelay(boolean)

public int 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.

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.

See Also

• setTrafficClass(int)
• SocketOptions.IP_TOS

public boolean isBound ()

Returns the binding state of the socket.

Note: Closing a socket doesn't clear its binding state, which means this method will return true for a closed socket (see isClosed()) if it was successfuly bound prior to being closed.

Returns

• true if the socket was successfuly bound to an address

See Also

• bind(SocketAddress)

public boolean isClosed ()

Returns the closed state of the socket.

Returns

• true if the socket has been closed

See Also

• close()

public boolean isConnected ()

Returns the connection state of the socket.

Note: Closing a socket doesn't clear its connection state, which means this method will return true for a closed socket (see isClosed()) if it was successfuly connected prior to being closed.

Returns

• true if the socket was successfuly connected to a server

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

See Also

• shutdownInput()

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

See Also

• shutdownOutput()

public void sendUrgentData (int data)

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.

public void setKeepAlive (boolean on)

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.

See Also

• getKeepAlive()

public void setOOBInline (boolean on)

Enable/disable SO_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 SO_OOBINLINE, false to disable.

Throws

SocketException	if there is an error in the underlying protocol, such as a TCP error.

See Also

• getOOBInline()

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

public synchronized void setReceiveBufferSize (int size)

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.

See Also

• getReceiveBufferSize()
• ServerSocket.setReceiveBufferSize(int)

public void setReuseAddress (boolean on)

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_REUSEADDR socket option, or the socket is closed.

See Also

• getReuseAddress()
• bind(SocketAddress)
• isClosed()
• isBound()

public synchronized void setSendBufferSize (int size)

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.

See Also

• getSendBufferSize()

public void setSoLinger (boolean on, int linger)

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.

See Also

• getSoLinger()

public synchronized void setSoTimeout (int timeout)

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.

See Also

• getSoTimeout()

public static synchronized void setSocketImplFactory (SocketImplFactory fac)

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()

public void setTcpNoDelay (boolean on)

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.

See Also

• getTcpNoDelay()

public void setTrafficClass (int tc)

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 integer, the least significant 8 bits of which represent the value of the TOS octet in IP packets sent by the socket. RFC 1349 defines the TOS values as follows:

• 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

See Also

• getTrafficClass()
• SocketOptions.IP_TOS

public void shutdownInput ()

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 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.

See Also

• shutdownOutput()
• close()
• setSoLinger(boolean, int)
• isInputShutdown()

public void shutdownOutput ()

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)
• isOutputShutdown()

public String toString ()

Converts this socket to a String.

Returns

• a string representation of this socket.