Module java.base
Package java.net

Class ServerSocket

  • All Implemented Interfaces:
    Closeable,AutoCloseable
    Direct Known Subclasses:
    SSLServerSocket

    public classServerSocketextendsObjectimplementsCloseable
    This class implements server sockets. A server socket waits for requests to come in over the network. It performs some operation based on that request, and then possibly returns a result to the requester.

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

    Since:
    1.0
    See Also:
    SocketImpl,setSocketFactory(java.net.SocketImplFactory),ServerSocketChannel

    • Constructor Detail

      • ServerSocket

        public ServerSocket()             throwsIOException
        Creates an unbound server socket.
        Throws:
        IOException - IO error when opening the socket.

      • ServerSocket

        public ServerSocket(int port)             throwsIOException
        Creates a server socket, bound to the specified port. A port number of0 means that the port number is automatically allocated, typically from an ephemeral port range. This port number can then be retrieved by callinggetLocalPort.

        The maximum queue length for incoming connection indications (a request to connect) is set to50. If a connection indication arrives when the queue is full, the connection is refused.

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

        If there is a security manager, itscheckListen method is called with theport argument as its argument to ensure the operation is allowed. This could result in a SecurityException.

        Parameters:
        port - the port number, or0 to use a port number that is automatically allocated.
        Throws:
        IOException - if an I/O error occurs when opening the socket.
        SecurityException - if a security manager exists and itscheckListen 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:
        SocketImpl,SocketImplFactory.createSocketImpl(),setSocketFactory(java.net.SocketImplFactory),SecurityManager.checkListen(int)

      • ServerSocket

        public ServerSocket(int port,                    int backlog)             throwsIOException
        Creates a server socket and binds it to the specified local port number, with the specified backlog. A port number of0 means that the port number is automatically allocated, typically from an ephemeral port range. This port number can then be retrieved by callinggetLocalPort.

        The maximum queue length for incoming connection indications (a request to connect) is set to thebacklog parameter. If a connection indication arrives when the queue is full, the connection is refused.

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

        If there is a security manager, itscheckListen method is called with theport argument as its argument to ensure the operation is allowed. This could result in a SecurityException. Thebacklog argument is the requested maximum number of pending connections on the socket. Its exact semantics are implementation specific. In particular, an implementation may impose a maximum length or may choose to ignore the parameter altogther. The value provided should be greater than0. If it is less than or equal to0, then an implementation specific default will be used.

        Parameters:
        port - the port number, or0 to use a port number that is automatically allocated.
        backlog - requested maximum length of the queue of incoming connections.
        Throws:
        IOException - if an I/O error occurs when opening the socket.
        SecurityException - if a security manager exists and itscheckListen 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:
        SocketImpl,SocketImplFactory.createSocketImpl(),setSocketFactory(java.net.SocketImplFactory),SecurityManager.checkListen(int)

      • ServerSocket

        public ServerSocket(int port,                    int backlog,InetAddress bindAddr)             throwsIOException
        Create a server with the specified port, listen backlog, and local IP address to bind to. ThebindAddr argument can be used on a multi-homed host for a ServerSocket that will only accept connect requests to one of its addresses. IfbindAddr is null, it will default accepting connections on any/all local addresses. The port must be between 0 and 65535, inclusive. A port number of0 means that the port number is automatically allocated, typically from an ephemeral port range. This port number can then be retrieved by callinggetLocalPort.

        If there is a security manager, this method calls itscheckListen method with theport argument as its argument to ensure the operation is allowed. This could result in a SecurityException. Thebacklog argument is the requested maximum number of pending connections on the socket. Its exact semantics are implementation specific. In particular, an implementation may impose a maximum length or may choose to ignore the parameter altogther. The value provided should be greater than0. If it is less than or equal to0, then an implementation specific default will be used.

        Parameters:
        port - the port number, or0 to use a port number that is automatically allocated.
        backlog - requested maximum length of the queue of incoming connections.
        bindAddr - the local InetAddress the server will bind to
        Throws:
        SecurityException - if a security manager exists and itscheckListen method doesn't allow the operation.
        IOException - if an I/O error occurs when opening the socket.
        IllegalArgumentException - if the port parameter is outside the specified range of valid port values, which is between 0 and 65535, inclusive.
        Since:
        1.1
        See Also:
        SocketOptions,SocketImpl,SecurityManager.checkListen(int)

    • Method Detail

      • bind

        public void bind(SocketAddress endpoint)          throwsIOException
        Binds theServerSocket to a specific address (IP address and port number).

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

        Parameters:
        endpoint - The IP address and port number to bind to.
        Throws:
        IOException - if the bind operation fails, or if the socket is already bound.
        SecurityException - if aSecurityManager is present and itscheckListen method doesn't allow the operation.
        IllegalArgumentException - if endpoint is a SocketAddress subclass not supported by this socket
        Since:
        1.4

      • bind

        public void bind(SocketAddress endpoint,                 int backlog)          throwsIOException
        Binds theServerSocket to a specific address (IP address and port number).

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

        Thebacklog argument is the requested maximum number of pending connections on the socket. Its exact semantics are implementation specific. In particular, an implementation may impose a maximum length or may choose to ignore the parameter altogther. The value provided should be greater than0. If it is less than or equal to0, then an implementation specific default will be used.

        Parameters:
        endpoint - The IP address and port number to bind to.
        backlog - requested maximum length of the queue of incoming connections.
        Throws:
        IOException - if the bind operation fails, or if the socket is already bound.
        SecurityException - if aSecurityManager is present and itscheckListen method doesn't allow the operation.
        IllegalArgumentException - if endpoint is a SocketAddress subclass not supported by this socket
        Since:
        1.4

      • getInetAddress

        public InetAddress getInetAddress()
        Returns the local address of this server socket.

        If the socket was bound prior to beingclosed, then this method will continue to return the local address after the socket is closed.

        If there is a security manager set, itscheckConnect 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, theloopback address is returned.

        Returns:
        the address to which this socket is bound, or the loopback address if denied by the security manager, ornull if the socket is unbound.
        See Also:
        SecurityManager.checkConnect(java.lang.String, int)

      • getLocalPort

        public int getLocalPort()
        Returns the port number on which this socket is listening.

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

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

      • getLocalSocketAddress

        public SocketAddress getLocalSocketAddress()
        Returns the address of the endpoint this socket is bound to.

        If the socket was bound prior to beingclosed, then this method will continue to return the address of the endpoint after the socket is closed.

        If there is a security manager set, itscheckConnect 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, aSocketAddress representing theloopback address and the local port to which the socket is bound is returned.

        Returns:
        aSocketAddress representing the local endpoint of this socket, or aSocketAddress representing the loopback address if denied by the security manager, ornull if the socket is not bound yet.
        Since:
        1.4
        See Also:
        getInetAddress(),getLocalPort(),bind(SocketAddress),SecurityManager.checkConnect(java.lang.String, int)

      • accept

        public Socket accept()              throwsIOException
        Listens for a connection to be made to this socket and accepts it. The method blocks until a connection is made.

        A new Sockets is created and, if there is a security manager, the security manager'scheckAccept method is called withs.getInetAddress().getHostAddress() ands.getPort() as its arguments to ensure the operation is allowed. This could result in a SecurityException.

        Returns:
        the new Socket
        Throws:
        IOException - if an I/O error occurs when waiting for a connection.
        SecurityException - if a security manager exists and itscheckAccept method doesn't allow the operation.
        SocketTimeoutException - if a timeout was previously set with setSoTimeout and the timeout has been reached.
        IllegalBlockingModeException - if this socket has an associated channel, the channel is in non-blocking mode, and there is no connection ready to be accepted
        See Also:
        SecurityManager.checkAccept(java.lang.String, int)

      • implAccept

        protected final void implAccept(Socket s)                         throwsIOException
        Subclasses of ServerSocket use this method to override accept() to return their own subclass of socket. So a FooServerSocket will typically hand this method anempty FooSocket. On return from implAccept the FooSocket will be connected to a client.
        Parameters:
        s - the Socket
        Throws:
        IllegalBlockingModeException - if this socket has an associated channel, and the channel is in non-blocking mode
        IOException - if an I/O error occurs when waiting for a connection.
        Since:
        1.1

      • getChannel

        public ServerSocketChannel getChannel()
        Returns the uniqueServerSocketChannel object associated with this socket, if any.

        A server socket will have a channel if, and only if, the channel itself was created via theServerSocketChannel.open method.

        Returns:
        the server-socket channel associated with this socket, ornull if this socket was not created for a channel
        Since:
        1.4

      • isBound

        public boolean isBound()
        Returns the binding state of the ServerSocket.
        Returns:
        true if the ServerSocket successfully bound to an address
        Since:
        1.4

      • isClosed

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

      • setSoTimeout

        public void setSoTimeout(int timeout)                  throwsSocketException
        Enable/disableSO_TIMEOUT with the specified timeout, in milliseconds. With this option set to a non-zero timeout, a call to accept() for this ServerSocket will block for only this amount of time. If the timeout expires, ajava.net.SocketTimeoutException is raised, though the ServerSocket is still valid. The optionmust 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:
        1.1
        See Also:
        getSoTimeout()

      • setReuseAddress

        public void setReuseAddress(boolean on)                     throwsSocketException
        Enable/disable theSO_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 theTIME_WAIT state or2MSL wait state). For applications using a well known socket address or port it may not be possible to bind a socket to the requiredSocketAddress if there is a connection in the timeout state involving the socket address or port.

        EnablingSO_REUSEADDR prior to binding the socket usingbind(SocketAddress) allows the socket to be bound even though a previous connection is in a timeout state.

        When aServerSocket is created the initial setting ofSO_REUSEADDR is not defined. Applications can usegetReuseAddress() to determine the initial setting ofSO_REUSEADDR.

        The behaviour whenSO_REUSEADDR is enabled or disabled after a socket is bound (SeeisBound()) is not defined.

        Parameters:
        on - whether to enable or disable the socket option
        Throws:
        SocketException - if an error occurs enabling or disabling theSO_REUSEADDR socket option, or the socket is closed.
        Since:
        1.4
        See Also:
        getReuseAddress(),bind(SocketAddress),isBound(),isClosed()

      • toString

        public String toString()
        Returns the implementation address and implementation port of this socket as aString.

        If there is a security manager set, itscheckConnect 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, anInetAddress representing theloopback address is returned as the implementation address.

        Overrides:
        toString in class Object
        Returns:
        a string representation of this socket.

      • setSocketFactory

        public static void setSocketFactory(SocketImplFactory fac)                             throwsIOException
        Sets the server socket implementation factory for the application. The factory can be specified only once.

        When an application creates a new server socket, the socket implementation factory'screateSocketImpl method is called to create the actual socket implementation.

        Passingnull 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'scheckSetFactory 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 has already been defined.
        SecurityException - if a security manager exists and itscheckSetFactory method doesn't allow the operation.
        See Also:
        SocketImplFactory.createSocketImpl(),SecurityManager.checkSetFactory()

      • setReceiveBufferSize

        public void setReceiveBufferSize(int size)                          throwsSocketException
        Sets a default proposed value for theSO_RCVBUF option for sockets accepted from thisServerSocket. The value actually set in the accepted socket must be determined by callingSocket.getReceiveBufferSize() after the socket is returned byaccept().

        The value ofSO_RCVBUF is used both to set the size of the internal socket receive buffer, and to set the size of the TCP receive window that is advertized to the remote peer.

        It is possible to change the value subsequently, by callingSocket.setReceiveBufferSize(int). However, if the application wishes to allow a receive window larger than 64K bytes, as defined by RFC1323 then the proposed value must be set in the ServerSocketbefore it is bound to a local address. This implies, that the ServerSocket must be created with the no-argument constructor, then setReceiveBufferSize() must be called and lastly the ServerSocket is bound to an address by calling bind().

        Failure to do this will not cause an error, and the buffer size may be set to the requested value but the TCP receive window in sockets accepted from this ServerSocket will be no larger than 64K bytes.

        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.
        IllegalArgumentException - if the value is 0 or is negative.
        Since:
        1.4
        See Also:
        getReceiveBufferSize()

      • getReceiveBufferSize

        public int getReceiveBufferSize()                         throwsSocketException
        Gets the value of theSO_RCVBUF option for thisServerSocket, that is the proposed buffer size that will be used for Sockets accepted from thisServerSocket.

        Note, the value actually set in the accepted socket is determined by callingSocket.getReceiveBufferSize().

        Returns:
        the value of theSO_RCVBUF option for thisSocket.
        Throws:
        SocketException - if there is an error in the underlying protocol, such as a TCP error.
        Since:
        1.4
        See Also:
        setReceiveBufferSize(int)

      • setPerformancePreferences

        public void setPerformancePreferences(int connectionTime,                                      int latency,                                      int bandwidth)
        Sets performance preferences for this ServerSocket.

        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. 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 bound will have no effect. This implies that in order to use this capability requires the socket to be created with the no-argument constructor.

        Parameters:
        connectionTime - Anint expressing the relative importance of a short connection time
        latency - Anint expressing the relative importance of low latency
        bandwidth - Anint expressing the relative importance of high bandwidth
        Since:
        1.5

      • setOption

        public <T> ServerSocket setOption(SocketOption<T> name,                                  T value)                           throwsIOException
        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 ofnull may be valid for some options.
        Returns:
        this ServerSocket
        Throws:
        UnsupportedOperationException - if the server 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 isnull
        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)                throwsIOException
        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 server socket does not support the option.
        IOException - if an I/O error occurs, or if the socket is closed.
        NullPointerException - if name isnull
        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 server 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