Class ServerSocket
- 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_RCVBUF
The size of the socket receive buffer SO_REUSEADDR
Re-use address
- Since:
- 1.0
- See Also:
-
Constructor Summary
ModifierConstructorDescriptionCreates 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.protected
ServerSocket
(SocketImpl impl) Creates a server socket with a user-specifiedSocketImpl
. -
Method Summary
Modifier and TypeMethodDescriptionaccept()
Listens for a connection to be made to this socket and accepts it.void
bind
(SocketAddress endpoint) Binds theServerSocket
to a specific address (IP address and port number).void
bind
(SocketAddress endpoint, int backlog) Binds theServerSocket
to a specific address (IP address and port number).void
close()
Closes this socket.Returns the uniqueServerSocketChannel
object associated with this socket, if any.Returns the local address of this server socket.int
Returns the port number on which this socket is listening.Returns the address of the endpoint this socket is bound to.<T> T
getOption
(SocketOption<T> name) Returns the value of a socket option.int
Gets the value of theSO_RCVBUF
option for thisServerSocket
, that is the proposed buffer size that will be used for Sockets accepted from thisServerSocket
.boolean
Tests ifSO_REUSEADDR
is enabled.int
Retrieve setting forSO_TIMEOUT
. 0 returns implies that the option is disabled (i.e., timeout of infinity).protected final void
implAccept
(Socket s) Subclasses of ServerSocket use this method to override accept() to return their own subclass of socket.boolean
isBound()
Returns the binding state of the ServerSocket.boolean
isClosed()
Returns the closed state of the ServerSocket.<T> ServerSocket
setOption
(SocketOption<T> name, T value) Sets the value of a socket option.void
setPerformancePreferences
(int connectionTime, int latency, int bandwidth) Sets performance preferences for this ServerSocket.void
setReceiveBufferSize
(int size) Sets a default proposed value for theSO_RCVBUF
option for sockets accepted from thisServerSocket
.void
setReuseAddress
(boolean on) Enable/disable theSO_REUSEADDR
socket option.static void
Deprecated.void
setSoTimeout
(int timeout) Enable/disableSO_TIMEOUT
with 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
.
-
Constructor Details
-
ServerSocket
Creates a server socket with a user-specifiedSocketImpl
.- Parameters:
impl
- an instance of a SocketImpl to use on the ServerSocket.- Throws:
NullPointerException
- if impl isnull
.- Since:
- 12
-
ServerSocket
Creates an unbound server socket.- Throws:
IOException
- IO error when opening the socket.
-
ServerSocket
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 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 createSocketImpl method is called to create the actual socket implementation. Otherwise a system-default socket implementation is created.
- 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.IllegalArgumentException
- if the port parameter is outside the specified range of valid port values, which is between 0 and 65535, inclusive.
-
ServerSocket
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 the
backlog
parameter. 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 createSocketImpl method is called to create the actual socket implementation. Otherwise a system-default socket implementation is created. The
backlog
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 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, 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.IllegalArgumentException
- if the port parameter is outside the specified range of valid port values, which is between 0 and 65535, inclusive.
-
ServerSocket
Create 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 of0
means that the port number is automatically allocated, typically from an ephemeral port range. This port number can then be retrieved by callinggetLocalPort
. 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 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, 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:
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
-
-
Method Details
-
bind
Binds theServerSocket
to 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, the socket is already bound or the socket is closed.IllegalArgumentException
- if endpoint is a SocketAddress subclass not supported by this socket- Since:
- 1.4
-
bind
Binds theServerSocket
to 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
backlog
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 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, the socket is already bound or the socket is closed.IllegalArgumentException
- if endpoint is a SocketAddress subclass not supported by this socket- Since:
- 1.4
-
getInetAddress
Returns 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.- Returns:
- the address to which this socket is bound,
or
null
if the socket is unbound.
-
getLocalPort
public 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.
-
getLocalSocketAddress
Returns 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.- Returns:
- a
SocketAddress
representing the local endpoint of this socket, ornull
if the socket is not bound yet. - Since:
- 1.4
- See Also:
-
accept
Listens 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 throwClosedByInterruptException
with 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
SocketException
with the interrupt status set.
- Implementation Note:
- An instance of this class using a system-default
SocketImpl
accepts sockets with aSocketImpl
of 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, the socket is not bound or the socket is closed.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
- The socket is associated
with a
-
implAccept
Subclasses 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
SocketImpl
of one type and the given socket has aSocketImpl
of a completely different type.- Implementation Note:
- An instance of this class using a system-default
SocketImpl
can accept a connection with a Socket using aSocketImpl
of the same type:IOException
is thrown if the Socket is using a customSocketImpl
. An instance of this class using a customSocketImpl
cannot 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 modeIOException
- 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
-
close
Closes this socket. Any thread currently blocked inaccept()
will throw aSocketException
.If this socket has an associated channel then the channel is closed as well.
Once closed, several of the methods defined by this class will throw an exception if invoked on the closed socket.
- Specified by:
close
in interfaceAutoCloseable
- Specified by:
close
in interfaceCloseable
- Throws:
IOException
- if an I/O error occurs when closing the socket.
-
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 the
ServerSocketChannel.open
method.- Returns:
- the server-socket channel associated with this socket,
or
null
if this socket was not created for a channel - Since:
- 1.4
-
isBound
public 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
true
after the socket is closed.- 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
Enable/disableSO_TIMEOUT
with 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, aSocketTimeoutException
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, or the socket is closed.IllegalArgumentException
- iftimeout
is negative- Since:
- 1.1
- See Also:
-
getSoTimeout
Retrieve setting forSO_TIMEOUT
. 0 returns implies that the option is disabled (i.e., timeout of infinity).- Returns:
- the
SO_TIMEOUT
value - Throws:
IOException
- if an I/O error occurs or the socket is closed.- Since:
- 1.1
- See Also:
-
setReuseAddress
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 the
TIME_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.Enabling
SO_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 a
ServerSocket
is created the initial setting ofSO_REUSEADDR
is not defined. Applications can usegetReuseAddress()
to determine the initial setting ofSO_REUSEADDR
.The behaviour when
SO_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
Tests ifSO_REUSEADDR
is enabled.- Returns:
- a
boolean
indicating whether or notSO_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:
-
toString
-
setSocketFactory
@Deprecated(since="17") public static void setSocketFactory(SocketImplFactory fac) throws IOException Deprecated.Use aServerSocketFactory
and subclassServerSocket
directly.
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, aServerSocket
can be created to use a custom implementation by extendingServerSocket
and 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
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.- 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.- See Also:
-
setReceiveBufferSize
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 of
SO_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 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, or the socket is closed.IllegalArgumentException
- if the value is 0 or is negative.- Since:
- 1.4
- See Also:
-
getReceiveBufferSize
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 calling
Socket.getReceiveBufferSize()
.- Returns:
- the value of the
SO_RCVBUF
option for thisSocket
. - 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:
-
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 timelatency
- Anint
expressing the relative importance of low latencybandwidth
- Anint
expressing the relative importance of high bandwidth- Since:
- 1.5
-
setOption
Sets the value of a socket option.- Type Parameters:
T
- The type of the socket option value- Parameters:
name
- The socket optionvalue
- 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
- Since:
- 9
-
getOption
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
- Since:
- 9
-
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
-
ServerSocketFactory
and subclassServerSocket
directly.