java.net
class Socket

java.lang.Object java.net.Socket

Direct Known Subclasses:

SSLSocket

Most common way to construct:

ServerSocket server = …;

Socket s = server.accept();

Based on 78 examples

public class Socket
extends Object

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

The actual work of the socket is performed by an instance of the SocketImpl class. An application, by changing the socket factory that creates the socket implementation, can configure itself to create sockets appropriate to the local firewall.

See Also (auto-generated):

Thread

ServerSocket

InputStream

Socket

public Socket()

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

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.

Socket

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

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.

Socket

public Socket(InetAddress address,
              int port,
              InetAddress localAddr,
              int localPort)
       throws IOException

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

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

Parameters:

address - the remote address

port - the remote port

localAddr - the local address the socket is bound to

localPort - the local port the socket is bound to

Throws:

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

Socket

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 {@link java.net.Proxy Proxy} object specifying what kind of proxying should be used.

Socket

protected Socket(SocketImpl impl)
          throws SocketException

Creates an unconnected Socket with a user-specified SocketImpl.

Parameters:

impl - an instance of a SocketImpl the subclass wishes to use on the Socket.

Throws:

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

Socket

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

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

If the specified host is null it is the equivalent of specifying the address as {@link java.net.InetAddress#getByName 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.

Socket

public Socket(String host,
              int port,
              boolean stream)
       throws 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 {@link java.net.InetAddress#getByName 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.

Socket

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

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

If the specified host is null it is the equivalent of specifying the address as {@link java.net.InetAddress#getByName 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.

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

localPort - the local port the socket is bound to

Throws:

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

bind

public void bind(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.

close

public synchronized void close()
                        throws IOException

Closes this socket.

Any thread currently blocked in an I/O operation upon this socket will throw a {@link 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 {@link java.io.InputStream InputStream} and {@link java.io.OutputStream 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.

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

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

getChannel

public SocketChannel getChannel()

Returns the unique {@link java.nio.channels.SocketChannel 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 {@link java.nio.channels.SocketChannel#open SocketChannel.open} or {@link java.nio.channels.ServerSocketChannel#accept ServerSocketChannel.accept} methods.

Returns:

the socket channel associated with this socket, or null if this socket was not created for a channel

getInetAddress

public InetAddress getInetAddress()

Returns the address to which the socket is connected.

Returns:

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

getInputStream

public InputStream getInputStream()
                           throws IOException

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 {@link 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 {@link java.io.InputStream#read read}.

• If there are no bytes buffered on the socket, or all buffered bytes have been consumed by {@link java.io.InputStream#read read}, then all subsequent calls to {@link java.io.InputStream#read read} will throw an {@link java.io.IOException IOException}.

• If there are no bytes buffered on the socket, and the socket has not been closed using {@link #close close}, then {@link java.io.InputStream#available available} will return 0.

Closing the returned {@link java.io.InputStream 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 {@link #shutdownInput()}

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.

getLocalAddress

public InetAddress getLocalAddress()

Gets the local address to which the socket is bound.

Returns:

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

getLocalPort

public int getLocalPort()

Returns the local port to which this socket is bound.

Returns:

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

getLocalSocketAddress

public SocketAddress getLocalSocketAddress()

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

Returns:

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

getOOBInline

public boolean getOOBInline()
                     throws SocketException

Tests if OOBINLINE is enabled.

Returns:

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.

getOutputStream

public OutputStream getOutputStream()
                             throws IOException

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 {@link java.nio.channels.IllegalBlockingModeException}.

Closing the returned {@link java.io.OutputStream 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.

getPort

public int getPort()

Returns the remote port to which this socket is connected.

Returns:

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

getReceiveBufferSize

public synchronized 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.

getRemoteSocketAddress

public SocketAddress getRemoteSocketAddress()

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

Returns:

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

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.

getSendBufferSize

public synchronized 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.

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.

getSoTimeout

public synchronized 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.

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.

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 {@link #setTrafficClass(int)} this method may return a different value than was previously set using the {@link #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.

isBound

public boolean isBound()

Returns the binding state of the socket.

Returns:

true if the socket successfuly bound to an address

isClosed

public boolean isClosed()

Returns the closed state of the socket.

Returns:

true if the socket has been closed

isConnected

public boolean isConnected()

Returns the connection state of the socket.

Returns:

true if the socket successfuly connected to a server

isInputShutdown

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

isOutputShutdown

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

sendUrgentData

public void sendUrgentData(int data)
                    throws IOException

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.

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.

setOOBInline

public void setOOBInline(boolean on)
                  throws SocketException

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.

Parameters:

on - true to enable OOBINLINE, false to disable.

Throws:

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

setPerformancePreferences

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

setReceiveBufferSize

public synchronized 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 {@link #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 {@link 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:

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

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 {@link #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 {@link #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_RESUEADDR socket option, or the socket is closed.

setSendBufferSize

public synchronized 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 {@link #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.

setSocketImplFactory

public static synchronized void setSocketImplFactory(SocketImplFactory fac)
                                              throws IOException

Sets the client socket implementation factory for the application. The factory can be specified only once.

When an application creates a new client socket, the socket implementation factory's createSocketImpl method is called to create the actual socket implementation.

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.

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.

setSoTimeout

public synchronized 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.

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.

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 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.

Parameters:

tc - an int value for the bitset.

Throws:

SocketException - if there is an error setting the traffic class or type-of-service

shutdownInput

public void shutdownInput()
                   throws IOException

Places the input stream for this socket at "end of stream". Any data sent to the input stream side of the socket is acknowledged and then silently discarded.

If you read from a socket input stream after invoking shutdownInput() on the socket, the stream will return EOF.

Throws:

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

shutdownOutput

public void shutdownOutput()
                    throws IOException

Disables the output stream for this socket. For a TCP socket, any previously written data will be sent followed by TCP's normal connection termination sequence. If you write to a socket output stream after invoking shutdownOutput() on the socket, the stream will throw an IOException.

Throws:

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

toString

public String toString()

Converts this socket to a String.

Overrides:

toString in class Object

Returns:

a string representation of this socket.