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.

The actual work of the socket is performed by an instance of the SocketImpl class.

The Socket class defines convenience methods to set and get several socket options. This class also defines the setOption and getOption methods to set and query socket options. A Socket support the following options:

Socket options
Option Name Description
SO_SNDBUF The size of the socket send buffer
SO_RCVBUF The size of the socket receive buffer
SO_KEEPALIVE Keep connection alive
SO_REUSEADDR Re-use address
SO_LINGER Linger on close if data is present (when configured in blocking mode only)
TCP_NODELAY Disable the Nagle algorithm
Additional (implementation specific) options may also be supported.
Since:
1.0
See Also:

  • Constructor Details

    • Socket

      public Socket()
      Creates an unconnected Socket.

      If the application has specified a client socket implementation factory, that factory's createSocketImpl method is called to create the actual socket implementation. Otherwise a system-default socket implementation is created.

      Since:
      1.1

    • 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 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.
      Since:
      1.5
      See Also:

    • 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.
      SecurityException - if impl is non-null and a security manager is set and its checkPermission method doesn't allow NetPermission("setSocketImpl").
      Since:
      1.1

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

      If the application has specified a client socket implementation factory, that factory's createSocketImpl method is called to create the actual socket implementation. Otherwise a system-default socket implementation 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:

    • 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 client socket implementation factory, that factory's createSocketImpl method is called to create the actual socket implementation. Otherwise a system-default socket implementation 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:

    • 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 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:
      1.1
      See Also:

    • 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 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:
      1.1
      See Also:

    • Socket

      @Deprecated(forRemoval=true, since="1.1") public Socket(String host, int port, boolean stream) throws IOException
      Deprecated, for removal: This API element is subject to removal in a future version.
      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 client socket implementation factory, that factory's createSocketImpl method is called to create the actual socket implementation. Otherwise a system-default socket implementation 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:

    • Socket

      @Deprecated(forRemoval=true, since="1.1") public Socket(InetAddress host, int port, boolean stream) throws IOException
      Deprecated, for removal: This API element is subject to removal in a future version.
      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 client socket implementation factory, that factory's createSocketImpl method is called to create the actual socket implementation. Otherwise a system-default socket implementation 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:

  • Method Details

    • connect

      public void connect(SocketAddress endpoint) throws IOException
      Connects this socket to the server.

      This method is interruptible in the following circumstances:

      1. The socket is associated with a SocketChannel. In that case, interrupting a thread establishing a connection will close the underlying channel and cause this method to throw ClosedByInterruptException with the interrupt status set.
      2. The socket uses the system-default socket implementation and a virtual thread is establishing a connection. In that case, interrupting the virtual thread will cause it to wakeup and close the socket. This method will then throw SocketException with the interrupt status set.
      Parameters:
      endpoint - the SocketAddress
      Throws:
      IOException - if an error occurs during the connection, the socket is already connected or the socket is closed
      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
      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.

      This method is interruptible in the following circumstances:

      1. The socket is associated with a SocketChannel. In that case, interrupting a thread establishing a connection will close the underlying channel and cause this method to throw ClosedByInterruptException with the interrupt status set.
      2. The socket uses the system-default socket implementation and a virtual thread is establishing a connection. In that case, interrupting the virtual thread will cause it to wakeup and close the socket. This method will then throw SocketException with the interrupt status set.
      Parameters:
      endpoint - the SocketAddress
      timeout - the timeout value to be used in milliseconds.
      Throws:
      IOException - if an error occurs during the connection, the socket is already connected or the socket is closed
      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, or if timeout is negative
      Since:
      1.4

    • 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, the socket is already bound or the socket is closed.
      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(int)

    • getInetAddress

      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. 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.
      Since:
      1.1
      See Also:

    • 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

      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:

    • getLocalSocketAddress

      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.
      Since:
      1.4
      See Also:

    • getChannel

      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
      Since:
      1.4

    • 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 IllegalBlockingModeException.

      Reading from the input stream is interruptible in the following circumstances:

      1. The socket is associated with a SocketChannel. In that case, interrupting a thread reading from the input stream will close the underlying channel and cause the read method to throw ClosedByInterruptException with the interrupt status set.
      2. The socket uses the system-default socket implementation and a virtual thread is reading from the input stream. In that case, interrupting the virtual thread will cause it to wakeup and close the socket. The read method will then throw SocketException with the interrupt status set.

      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()

    • 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 IllegalBlockingModeException.

      Writing to the output stream is interruptible in the following circumstances:

      1. The socket is associated with a SocketChannel. In that case, interrupting a thread writing to the output stream will close the underlying channel and cause the write method to throw ClosedByInterruptException with the interrupt status set.
      2. The socket uses the system-default socket implementation and a virtual thread is writing to the output stream. In that case, interrupting the virtual thread will cause it to wakeup and close the socket. The write method will then throw SocketException with the interrupt status set.

      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, the socket is not connected or the socket is closed.

    • 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, or the socket is closed.
      Since:
      1.1
      See Also:

    • 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, or the socket is closed.
      Since:
      1.1
      See Also:

    • 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, or the socket is closed.
      IllegalArgumentException - if the linger value is negative.
      Since:
      1.1
      See Also:

    • 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, or the socket is closed.
      Since:
      1.1
      See Also:

    • 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.
      Since:
      1.4

    • 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, or the socket is closed.
      Since:
      1.4
      See Also:

    • getOOBInline

      public boolean getOOBInline() throws SocketException
      Tests if SO_OOBINLINE is enabled.
      Returns:
      a boolean indicating whether or not SO_OOBINLINE is enabled.
      Throws:
      SocketException - if there is an error in the underlying protocol, such as a TCP error, or the socket is closed.
      Since:
      1.4
      See Also:

    • setSoTimeout

      public void setSoTimeout(int timeout) throws SocketException
      Enable/disable SO_TIMEOUT with the specified timeout, in milliseconds. With this option set to a positive timeout value, 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. A timeout of zero is interpreted as an infinite timeout. The option must be enabled prior to entering the blocking operation to have effect.
      Parameters:
      timeout - the specified timeout, in milliseconds.
      Throws:
      SocketException - if there is an error in the underlying protocol, such as a TCP error, or the socket is closed.
      IllegalArgumentException - if timeout is negative
      Since:
      1.1
      See Also:

    • 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, or the socket is closed.
      Since:
      1.1
      See Also:

    • 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, or the socket is closed.
      IllegalArgumentException - if the value is 0 or is negative.
      Since:
      1.2
      See Also:

    • 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, or the socket is closed.
      Since:
      1.2
      See Also:

    • 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 advertised 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, or the socket is closed.
      Since:
      1.2
      See Also:

    • 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, or the socket is closed.
      Since:
      1.2
      See Also:

    • 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, or the socket is closed.
      Since:
      1.3
      See Also:

    • 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, or the socket is closed.
      Since:
      1.3
      See Also:

    • 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, or the socket is closed.
      Since:
      1.4
      See Also:

    • 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, or the socket is closed.
      Since:
      1.4
      See Also:

    • 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

      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, or the socket is closed.
      Since:
      1.4
      See Also:

    • 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) and several of the methods defined by this class will throw an exception if invoked on the closed socket. 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 AutoCloseable
      Specified by:
      close in interface Closeable
      Throws:
      IOException - if an I/O error occurs when closing this socket.
      See Also:
      • isClosed(int)

    • 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 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, the socket is not connected or the socket is closed.
      Since:
      1.3
      See Also:

    • 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, the socket is not connected or the socket is closed.
      Since:
      1.3
      See Also:

    • 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 successfully connected prior to being closed.

      Returns:
      true if the socket was successfully 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 successfully bound prior to being closed.

      Returns:
      true if the socket was successfully bound to an address
      Since:
      1.4
      See Also:

    • isClosed

      public boolean isClosed()
      Returns the closed state of the socket.
      Returns:
      true if the socket has been closed
      Since:
      1.4
      See Also:

    • 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
      Since:
      1.4
      See Also:

    • 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
      Since:
      1.4
      See Also:

    • setSocketImplFactory

      @Deprecated(since="17") public static void setSocketImplFactory(SocketImplFactory fac) throws IOException
      Deprecated.
      Use a SocketFactory and subclass Socket directly.
      This method provided a way in early JDK releases to replace the system wide implementation of Socket. It has been mostly obsolete since Java 1.4. If required, a Socket can be created to use a custom implementation by extending Socket and using the protected constructor that takes an implementation as a parameter.
      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:

    • 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
      Since:
      1.5

    • setOption

      public <T> Socket setOption(SocketOption<T> name, T value) throws IOException
      Sets the value of a socket option.
      Type Parameters:
      T - The type of the socket option value
      Parameters:
      name - The socket option
      value - The value of the socket option. A value of null may be valid for some options.
      Returns:
      this Socket
      Throws:
      UnsupportedOperationException - if the socket does not support the option.
      IllegalArgumentException - if the value is not valid for the option.
      IOException - if an I/O error occurs, or if the socket is closed.
      NullPointerException - if name is null
      SecurityException - if a security manager is set and if the socket option requires a security permission and if the caller does not have the required permission. StandardSocketOptions do not require any security permission.
      Since:
      9

    • getOption

      public <T> T getOption(SocketOption<T> name) throws IOException
      Returns the value of a socket option.
      Type Parameters:
      T - The type of the socket option value
      Parameters:
      name - The socket option
      Returns:
      The value of the socket option.
      Throws:
      UnsupportedOperationException - if the socket does not support the option.
      IOException - if an I/O error occurs, or if the socket is closed.
      NullPointerException - if name is null
      SecurityException - if a security manager is set and if the socket option requires a security permission and if the caller does not have the required permission. StandardSocketOptions do not require any security permission.
      Since:
      9

    • supportedOptions

      public Set<SocketOption<?>> supportedOptions()
      Returns a set of the socket options supported by this socket. This method will continue to return the set of options even after the socket has been closed.
      Returns:
      A set of the socket options supported by this socket. This set may be empty if the socket's SocketImpl cannot be created.
      Since:
      9