- All Implemented Interfaces:
- Closeable,- AutoCloseable
- Direct Known Subclasses:
- SSLServerSocket
 The actual work of the server socket is performed by an instance
 of the SocketImpl class.
 
 The ServerSocket 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 ServerSocket supports the following options:
 
Additional (implementation specific) options may also be supported.
Option Name Description SO_RCVBUFThe size of the socket receive buffer SO_REUSEADDRRe-use address 
- Since:
- 1.0
- See Also:
- 
Constructor SummaryConstructorsModifierConstructorDescriptionCreates an unbound server socket.ServerSocket(int port) Creates a server socket, bound to the specified port.ServerSocket(int port, int backlog) Creates a server socket and binds it to the specified local port number, with the specified backlog.ServerSocket(int port, int backlog, InetAddress bindAddr) Create a server with the specified port, listen backlog, and local IP address to bind to.protectedServerSocket(SocketImpl impl) Creates a server socket with a user-specifiedSocketImpl.
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Method SummaryModifier and TypeMethodDescriptionaccept()Listens for a connection to be made to this socket and accepts it.voidbind(SocketAddress endpoint) Binds theServerSocketto a specific address (IP address and port number).voidbind(SocketAddress endpoint, int backlog) Binds theServerSocketto a specific address (IP address and port number).voidclose()Closes this socket.Returns the uniqueServerSocketChannelobject associated with this socket, if any.Returns the local address of this server socket.intReturns the port number on which this socket is listening.Returns the address of the endpoint this socket is bound to.<T> TgetOption(SocketOption<T> name) Returns the value of a socket option.intGets the value of theSO_RCVBUFoption for thisServerSocket, that is the proposed buffer size that will be used for Sockets accepted from thisServerSocket.booleanTests ifSO_REUSEADDRis enabled.intRetrieve setting forSO_TIMEOUT. 0 returns implies that the option is disabled (i.e., timeout of infinity).protected final voidimplAccept(Socket s) Subclasses of ServerSocket use this method to override accept() to return their own subclass of socket.booleanisBound()Returns the binding state of the ServerSocket.booleanisClosed()Returns the closed state of the ServerSocket.<T> ServerSocketsetOption(SocketOption<T> name, T value) Sets the value of a socket option.voidsetPerformancePreferences(int connectionTime, int latency, int bandwidth) Sets performance preferences for this ServerSocket.voidsetReceiveBufferSize(int size) Sets a default proposed value for theSO_RCVBUFoption for sockets accepted from thisServerSocket.voidsetReuseAddress(boolean on) Enable/disable theSO_REUSEADDRsocket option.static voidDeprecated.voidsetSoTimeout(int timeout) Enable/disableSO_TIMEOUTwith the specified timeout, in milliseconds.Set<SocketOption<?>> Returns a set of the socket options supported by this server socket.toString()Returns the implementation address and implementation port of this socket as aString.
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Constructor Details- 
ServerSocketCreates a server socket with a user-specifiedSocketImpl.- Parameters:
- impl- an instance of a SocketImpl to use on the ServerSocket.
- Throws:
- NullPointerException- if impl is- null.
- SecurityException- if a security manager is set and its- checkPermissionmethod doesn't allow- NetPermission("setSocketImpl").
- Since:
- 12
 
- 
ServerSocketCreates an unbound server socket.- Throws:
- IOException- IO error when opening the socket.
 
- 
ServerSocketCreates a server socket, bound to the specified port. A port number of0means 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 50. If a connection indication arrives when the queue is full, the connection is refused.If the application has specified a server socket implementation factory, that factory's createSocketImplmethod is called to create the actual socket implementation. Otherwise a system-default socket implementation is created.If there is a security manager, its checkListenmethod is called with theportargument as its argument to ensure the operation is allowed. This could result in a SecurityException.- Parameters:
- port- the port number, or- 0to 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 its- checkListenmethod 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:
 
- 
ServerSocketCreates a server socket and binds it to the specified local port number, with the specified backlog. A port number of0means 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 the backlogparameter. If a connection indication arrives when the queue is full, the connection is refused.If the application has specified a server socket implementation factory, that factory's createSocketImplmethod is called to create the actual socket implementation. Otherwise a system-default socket implementation is created.If there is a security manager, its checkListenmethod is called with theportargument as its argument to ensure the operation is allowed. This could result in a SecurityException. Thebacklogargument 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 altogether. 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, or- 0to 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 its- checkListenmethod 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:
 
- 
ServerSocketCreate a server with the specified port, listen backlog, and local IP address to bind to. The bindAddr argument can be used on a multi-homed host for a ServerSocket that will only accept connect requests to one of its addresses. If bindAddr is null, it will default accepting connections on any/all local addresses. The port must be between 0 and 65535, inclusive. A port number of0means 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 its checkListenmethod with theportargument as its argument to ensure the operation is allowed. This could result in a SecurityException. Thebacklogargument 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 altogether. 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, or- 0to 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 its- checkListenmethod 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:
 
 
- 
- 
Method Details- 
bindBinds theServerSocketto a specific address (IP address and port number).If the address is null, 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 a- SecurityManageris present and its- checkListenmethod doesn't allow the operation.
- IllegalArgumentException- if endpoint is a SocketAddress subclass not supported by this socket
- Since:
- 1.4
 
- 
bindBinds theServerSocketto a specific address (IP address and port number).If the address is null, then the system will pick up an ephemeral port and a valid local address to bind the socket.The backlogargument 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 altogether. 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 a- SecurityManageris present and its- checkListenmethod doesn't allow the operation.
- IllegalArgumentException- if endpoint is a SocketAddress subclass not supported by this socket
- Since:
- 1.4
 
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getInetAddressReturns the local address of this server socket.If the socket was bound prior to being closed, then this method will continue to return the local address after the socket is closed.If there is a security manager set, its checkConnectmethod is called with the local address and-1as its arguments to see if the operation is allowed. If the operation is not allowed, theloopbackaddress is returned.- Returns:
- the address to which this socket is bound,
          or the loopback address if denied by the security manager,
          or nullif the socket is unbound.
- See Also:
 
- 
getLocalPortpublic int getLocalPort()Returns the port number on which this socket is listening.If the socket was bound prior to being closed, 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.
 
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getLocalSocketAddressReturns the address of the endpoint this socket is bound to.If the socket was bound prior to being closed, then this method will continue to return the address of the endpoint after the socket is closed.If there is a security manager set, its checkConnectmethod is called with the local address and-1as its arguments to see if the operation is allowed. If the operation is not allowed, aSocketAddressrepresenting theloopbackaddress and the local port to which the socket is bound is returned.- Returns:
- a SocketAddressrepresenting the local endpoint of this socket, or aSocketAddressrepresenting the loopback address if denied by the security manager, ornullif the socket is not bound yet.
- Since:
- 1.4
- See Also:
 
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acceptListens for a connection to be made to this socket and accepts it. The method blocks until a connection is made.This method is interruptible in the following circumstances: -  The socket is associated
        with a ServerSocketChannel. In that case, interrupting a thread accepting a connection will close the underlying channel and cause this method to throwClosedByInterruptExceptionwith the interrupt status set.
-  The socket uses the system-default socket implementation and a
        virtual thread is accepting a
        connection. In that case, interrupting the virtual thread will
        cause it to wakeup and close the socket. This method will then throw
        SocketExceptionwith the interrupt status set.
 A new Socket sis created and, if there is a security manager, the security manager'scheckAcceptmethod is called withs.getInetAddress().getHostAddress()ands.getPort()as its arguments to ensure the operation is allowed. This could result in a SecurityException.- Implementation Note:
- An instance of this class using a system-default SocketImplaccepts sockets with aSocketImplof the same type, regardless of the client socket implementation factory, if one has been set.
- Returns:
- the new Socket
- Throws:
- IOException- if an I/O error occurs when waiting for a connection.
- SecurityException- if a security manager exists and its- checkAcceptmethod 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:
 
-  The socket is associated
        with a 
- 
implAcceptSubclasses of ServerSocket use this method to override accept() to return their own subclass of socket. So a FooServerSocket will typically hand this method a newly created, unbound, FooSocket. On return from implAccept the FooSocket will be connected to a client.The behavior of this method is unspecified when invoked with a socket that is not newly created and unbound. Any socket options set on the given socket prior to invoking this method may or may not be preserved when the connection is accepted. It may not be possible to accept a connection when this socket has a SocketImplof one type and the given socket has aSocketImplof a completely different type.- Implementation Note:
- An instance of this class using a system-default SocketImplcan accept a connection with a Socket using aSocketImplof the same type:IOExceptionis thrown if the Socket is using a customSocketImpl. An instance of this class using a customSocketImplcannot accept a connection with a Socket using a system-defaultSocketImpl.
- 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, or if it is not possible for this socket to accept a connection with the given socket
- Since:
- 1.1
 
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closeCloses this socket. Any thread currently blocked inaccept()will throw aSocketException.If this socket has an associated channel then the channel is closed as well. - Specified by:
- closein interface- AutoCloseable
- Specified by:
- closein interface- Closeable
- Throws:
- IOException- if an I/O error occurs when closing the socket.
 
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getChannelReturns the uniqueServerSocketChannelobject associated with this socket, if any.A server socket will have a channel if, and only if, the channel itself was created via the ServerSocketChannel.openmethod.- Returns:
- the server-socket channel associated with this socket,
          or nullif this socket was not created for a channel
- Since:
- 1.4
 
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isBoundpublic boolean isBound()Returns the binding state of the ServerSocket.If the socket was bound prior to being closed, then this method will continue to return trueafter the socket is closed.- Returns:
- true if the ServerSocket successfully bound to an address
- Since:
- 1.4
 
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isClosedpublic boolean isClosed()Returns the closed state of the ServerSocket.- Returns:
- true if the socket has been closed
- Since:
- 1.4
 
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setSoTimeoutEnable/disableSO_TIMEOUTwith the specified timeout, in milliseconds. With this option set to a positive timeout value, a call to accept() for this ServerSocket will block for only this amount of time. If the timeout expires, a java.net.SocketTimeoutException is raised, though the ServerSocket 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
- IllegalArgumentException- if- timeoutis negative
- Since:
- 1.1
- See Also:
 
- 
getSoTimeoutRetrieve setting forSO_TIMEOUT. 0 returns implies that the option is disabled (i.e., timeout of infinity).- Returns:
- the SO_TIMEOUTvalue
- Throws:
- IOException- if an I/O error occurs
- Since:
- 1.1
- See Also:
 
- 
setReuseAddressEnable/disable theSO_REUSEADDRsocket 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_WAITstate or2MSLwait state). For applications using a well known socket address or port it may not be possible to bind a socket to the requiredSocketAddressif there is a connection in the timeout state involving the socket address or port.Enabling SO_REUSEADDRprior to binding the socket usingbind(SocketAddress)allows the socket to be bound even though a previous connection is in a timeout state.When a ServerSocketis created the initial setting ofSO_REUSEADDRis not defined. Applications can usegetReuseAddress()to determine the initial setting ofSO_REUSEADDR.The behaviour when SO_REUSEADDRis 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 the- SO_REUSEADDRsocket option, or the socket is closed.
- Since:
- 1.4
- See Also:
 
- 
getReuseAddressTests ifSO_REUSEADDRis enabled.- Returns:
- a booleanindicating whether or notSO_REUSEADDRis enabled.
- Throws:
- SocketException- if there is an error in the underlying protocol, such as a TCP error.
- Since:
- 1.4
- See Also:
 
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toStringReturns the implementation address and implementation port of this socket as aString.If there is a security manager set, and this socket is bound, its checkConnectmethod is called with the local address and-1as its arguments to see if the operation is allowed. If the operation is not allowed, anInetAddressrepresenting theloopbackaddress is returned as the implementation address.
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setSocketFactory@Deprecated(since="17") public static void setSocketFactory(SocketImplFactory fac) throws IOException Deprecated.Use aServerSocketFactoryand subclassServerSocketdirectly.
 This method provided a way in early JDK releases to replace the system wide implementation ofServerSocket. It has been mostly obsolete since Java 1.4. If required, aServerSocketcan be created to use a custom implementation by extendingServerSocketand using the protected constructor that takes an implementation as a parameter.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's createSocketImplmethod is called to create the actual socket implementation.Passing nullto 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 checkSetFactorymethod 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 its- checkSetFactorymethod doesn't allow the operation.
- See Also:
 
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setReceiveBufferSizeSets a default proposed value for theSO_RCVBUFoption 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 of SO_RCVBUFis used both to set the size of the internal socket receive buffer, and to set the size of the TCP receive window that is advertised to the remote peer.It is possible to change the value subsequently, by calling Socket.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 ServerSocket before 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:
 
- 
getReceiveBufferSizeGets the value of theSO_RCVBUFoption 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 calling Socket.getReceiveBufferSize().- Returns:
- the value of the SO_RCVBUFoption for thisSocket.
- Throws:
- SocketException- if there is an error in the underlying protocol, such as a TCP error.
- Since:
- 1.4
- See Also:
 
- 
setPerformancePreferencespublic 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- An- intexpressing the relative importance of a short connection time
- latency- An- intexpressing the relative importance of low latency
- bandwidth- An- intexpressing the relative importance of high bandwidth
- Since:
- 1.5
 
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setOptionSets 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- nullmay 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 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.- StandardSocketOptionsdo not require any security permission.
- Since:
- 9
 
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getOptionReturns 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 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.- StandardSocketOptionsdo not require any security permission.
- Since:
- 9
 
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supportedOptionsReturns 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
 
 
- 
ServerSocketFactoryand subclassServerSocketdirectly.