java.net

Class Socket

java.lang.Object

java.net.Socket

All Implemented Interfaces:

Closeable, AutoCloseable

Direct Known Subclasses:

SSLSocket

public class Socket
extends Object
implements Closeable

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

Since:

JDK1.0

Constructor Summary

Constructors

Constructor and Description
Socket() Creates an unconnected socket, with the system-default type of SocketImpl.
Socket(InetAddress address, int port) Creates a stream socket and connects it to the specified port number at the specified IP address.
Socket(InetAddress 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) 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

Modifier and Type	Method and Description
void	bind(SocketAddress bindpoint) Binds the socket to a local address.
void	close() Closes this socket.
void	connect(SocketAddress endpoint) Connects this socket to the server.
void	connect(SocketAddress endpoint, int timeout) Connects this socket to the server with a specified timeout value.
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.
int	getReceiveBufferSize() Gets the value of the SO_RCVBUF option for this Socket, that is the buffer size used by the platform for input on this Socket.
SocketAddress	getRemoteSocketAddress() Returns the address of the endpoint this socket is connected to, or null if it is unconnected.
boolean	getReuseAddress() Tests if SO_REUSEADDR is enabled.
int	getSendBufferSize() Get value of the SO_SNDBUF option for this Socket, that is the buffer size used by the platform for output on this Socket.
int	getSoLinger() Returns setting for SO_LINGER.
int	getSoTimeout() Returns setting for SO_TIMEOUT.
boolean	getTcpNoDelay() Tests if TCP_NODELAY is enabled.
int	getTrafficClass() Gets traffic class or type-of-service in the IP header for packets sent from this Socket
boolean	isBound() Returns the binding state of the socket.
boolean	isClosed() Returns the closed state of the socket.
boolean	isConnected() Returns the connection state of the socket.
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	setReceiveBufferSize(int size) Sets the SO_RCVBUF option to the specified value for this Socket.
void	setReuseAddress(boolean on) Enable/disable the SO_REUSEADDR socket option.
void	setSendBufferSize(int size) Sets the SO_SNDBUF option to the specified value for this Socket.
void	setSoLinger(boolean on, int linger) Enable/disable SO_LINGER with the specified linger time in seconds.
void	setSoTimeout(int timeout) Enable/disable SO_TIMEOUT with the specified timeout, in milliseconds.
void	setTcpNoDelay(boolean on) Enable/disable TCP_NODELAY (disable/enable Nagle's algorithm).
void	setTrafficClass(int tc) Sets traffic class or type-of-service octet in the IP header for packets sent from this Socket.
String	toString() Converts this socket to a String.

Methods inherited from class java.lang.Object

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

Constructor Detail

Socket

public Socket()

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

Since:

JDK1.1

Socket

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

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

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

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

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

Parameters:

host - the host name, or null for the loopback address.

port - the port number.

Throws:

UnknownHostException - if the IP address of the host could not be determined.

IOException - if an I/O error occurs when creating the socket.

SecurityException - if a security manager exists and its checkConnect method doesn't allow the operation.

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

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.

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.

Socket

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

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

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

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.

Since:

JDK1.1

Socket

public Socket(InetAddress address,
              int port,
              @Nullable
              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 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.

Since:

JDK1.1

Method Detail

connect

public void connect(SocketAddress endpoint)
             throws IOException

Connects this socket to the server.

Parameters:

endpoint - the SocketAddress

Throws:

IOException - if an error occurs during the connection

IllegalArgumentException - if endpoint is null or is a SocketAddress subclass not supported by this socket

Since:

1.4

connect

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

Connects this socket to the server with a specified timeout value. A timeout of zero is interpreted as an infinite timeout. The connection will then block until established or an error occurs.

Parameters:

endpoint - the SocketAddress

timeout - the timeout value to be used in milliseconds.

Throws:

IOException - if an error occurs during the connection

SocketTimeoutException - if timeout expires before connecting

IllegalArgumentException - if endpoint is null or is a SocketAddress subclass not supported by this socket

Since:

1.4

bind

public void bind(@Nullable
                 SocketAddress bindpoint)
          throws IOException

Binds the socket to a local address.

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

Parameters:

bindpoint - the SocketAddress to bind to

Throws:

IOException - if the bind operation fails, or if the socket is already bound.

IllegalArgumentException - if bindpoint is a SocketAddress subclass not supported by this socket

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

Since:

1.4

See Also:

isBound()

getInetAddress

@Nullable
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.

getLocalAddress

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.

Returns:

the local address to which the socket is bound, or the wildcard address if the socket is closed or not bound yet.

Since:

JDK1.1

getPort

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.

getLocalPort

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.

getRemoteSocketAddress

@Nullable
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.

Since:

1.4

See Also:

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

getLocalSocketAddress

@Nullable
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.

Returns:

a SocketAddress representing the local endpoint of this socket, or null if the socket is not bound yet.

Since:

1.4

See Also:

getLocalAddress(), getLocalPort(), bind(SocketAddress)

getInputStream

public InputStream getInputStream()
                           throws IOException

Returns an input stream for this socket.

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 or the socket is not connected.

getOutputStream

public OutputStream getOutputStream()
                             throws IOException

Returns an output stream for this socket.

Closing the returned OutputStream will close the associated socket.

Returns:

an output stream for writing bytes to this socket.

Throws:

IOException - if an I/O error occurs when creating the output stream or if the socket is not connected.

setTcpNoDelay

public void setTcpNoDelay(boolean on)
                   throws SocketException

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

Parameters:

on - true to enable TCP_NODELAY, false to disable.

Throws:

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

Since:

JDK1.1

See Also:

getTcpNoDelay()

getTcpNoDelay

public boolean getTcpNoDelay()
                      throws SocketException

Tests if TCP_NODELAY is enabled.

Returns:

a boolean indicating whether or not TCP_NODELAY is enabled.

Throws:

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

Since:

JDK1.1

See Also:

setTcpNoDelay(boolean)

setSoLinger

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

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

Parameters:

on - whether or not to linger on.

linger - how long to linger for, if on is true.

Throws:

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

IllegalArgumentException - if the linger value is negative.

Since:

JDK1.1

See Also:

getSoLinger()

getSoLinger

public int getSoLinger()
                throws SocketException

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

Returns:

the setting for SO_LINGER.

Throws:

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

Since:

JDK1.1

See Also:

setSoLinger(boolean, int)

setOOBInline

public void setOOBInline(boolean on)
                  throws SocketException

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.

Since:

1.4

See Also:

getOOBInline()

getOOBInline

public boolean getOOBInline()
                     throws SocketException

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.

Since:

1.4

See Also:

setOOBInline(boolean)

setSoTimeout

public void setSoTimeout(int timeout)
                  throws SocketException

Enable/disable SO_TIMEOUT with the specified timeout, in milliseconds. With this option set to a non-zero timeout, a read() call on the InputStream associated with this Socket will block for only this amount of time. If the timeout expires, a java.net.SocketTimeoutException is raised, though the Socket is still valid. The option must be enabled prior to entering the blocking operation to have effect. The timeout must be > 0. A timeout of zero is interpreted as an infinite timeout.

Parameters:

timeout - the specified timeout, in milliseconds.

Throws:

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

Since:

JDK 1.1

See Also:

getSoTimeout()

getSoTimeout

public int getSoTimeout()
                 throws SocketException

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

Returns:

the setting for SO_TIMEOUT

Throws:

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

Since:

JDK1.1

See Also:

setSoTimeout(int)

setSendBufferSize

public void setSendBufferSize(int size)
                       throws SocketException

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

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

Parameters:

size - the size to which to set the send buffer size. This value must be greater than 0.

Throws:

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

IllegalArgumentException - if the value is 0 or is negative.

Since:

1.2

See Also:

getSendBufferSize()

getSendBufferSize

public int getSendBufferSize()
                      throws SocketException

Get value of the SO_SNDBUF option for this Socket, that is the buffer size used by the platform for output on this Socket.

Returns:

the value of the SO_SNDBUF option for this Socket.

Throws:

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

Since:

1.2

See Also:

setSendBufferSize(int)

setReceiveBufferSize

public void setReceiveBufferSize(int size)
                          throws SocketException

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

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

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

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

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

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

Parameters:

size - the size to which to set the receive buffer size. This value must be greater than 0.

Throws:

IllegalArgumentException - if the value is 0 or is negative.

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

Since:

1.2

See Also:

getReceiveBufferSize(), ServerSocket.setReceiveBufferSize(int)

getReceiveBufferSize

public int getReceiveBufferSize()
                         throws SocketException

Gets the value of the SO_RCVBUF option for this Socket, that is the buffer size used by the platform for input on this Socket.

Returns:

the value of the SO_RCVBUF option for this Socket.

Throws:

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

Since:

1.2

See Also:

setReceiveBufferSize(int)

setKeepAlive

public void setKeepAlive(boolean on)
                  throws SocketException

Enable/disable SO_KEEPALIVE.

Parameters:

on - whether or not to have socket keep alive turned on.

Throws:

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

Since:

1.3

See Also:

getKeepAlive()

getKeepAlive

public boolean getKeepAlive()
                     throws SocketException

Tests if SO_KEEPALIVE is enabled.

Returns:

a boolean indicating whether or not SO_KEEPALIVE is enabled.

Throws:

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

Since:

1.3

See Also:

setKeepAlive(boolean)

setTrafficClass

public void setTrafficClass(int tc)
                     throws SocketException

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

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

Notes:

For Internet Protocol v4 the value consists of an 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

Since:

1.4

See Also:

getTrafficClass(), SocketOptions.IP_TOS

getTrafficClass

public int getTrafficClass()
                    throws SocketException

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

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

Returns:

the traffic class or type-of-service already set

Throws:

SocketException - if there is an error obtaining the traffic class or type-of-service value.

Since:

1.4

See Also:

setTrafficClass(int), SocketOptions.IP_TOS

setReuseAddress

public void setReuseAddress(boolean on)
                     throws SocketException

Enable/disable the SO_REUSEADDR socket option.

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

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

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

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

Parameters:

on - whether to enable or disable the socket option

Throws:

SocketException - if an error occurs enabling or disabling the SO_REUSEADDR socket option, or the socket is closed.

Since:

1.4

See Also:

getReuseAddress(), bind(SocketAddress), isClosed(), isBound()

getReuseAddress

public boolean getReuseAddress()
                        throws SocketException

Tests if SO_REUSEADDR is enabled.

Returns:

a boolean indicating whether or not SO_REUSEADDR is enabled.

Throws:

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

Since:

1.4

See Also:

setReuseAddress(boolean)

close

public void close()
           throws IOException

Closes this socket.

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

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

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

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

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

Throws:

IOException - if an I/O error occurs when closing this socket.

See Also:

isClosed()

toString

public String toString()

Converts this socket to a String.

Overrides:

toString in class Object

Returns:

a string representation of this socket.

isConnected

public boolean isConnected()

Returns the connection state of the socket.

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

Since:

1.4

isBound

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

Since:

1.4

See Also:

bind(java.net.SocketAddress)

isClosed

public boolean isClosed()

Returns the closed state of the socket.

Returns:

true if the socket has been closed

Since:

1.4

See Also:

close()