Closeable
, AutoCloseable
SSLServerSocket
public class ServerSocket extends Object implements Closeable
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
Modifier | Constructor | Description |
---|---|---|
Creates an unbound server socket. |
||
Creates a server socket, bound to the specified port. |
||
Creates a server socket and binds it to the specified local port number, with the specified backlog. |
||
Create a server with the specified port, listen backlog, and local IP address to bind to. |
||
protected |
Creates a server socket with a user-specified SocketImpl . |
Modifier and Type | Method | Description |
---|---|---|
Socket |
accept() |
Listens for a connection to be made to this socket and accepts it. |
void |
bind |
Binds the ServerSocket to a specific address (IP address and port number). |
void |
bind |
Binds the ServerSocket to a specific address (IP address and port number). |
void |
close() |
Closes this socket. |
ServerSocketChannel |
getChannel() |
Returns the unique ServerSocketChannel object associated with this socket, if any. |
InetAddress |
getInetAddress() |
Returns the local address of this server socket. |
int |
getLocalPort() |
Returns the port number on which this socket is listening. |
SocketAddress |
getLocalSocketAddress() |
Returns the address of the endpoint this socket is bound to. |
<T> T |
getOption |
Returns the value of a socket option. |
int |
getReceiveBufferSize() |
Gets the value of the SO_RCVBUF option for this ServerSocket , that is the proposed buffer size that will be used for Sockets accepted from this ServerSocket . |
boolean |
getReuseAddress() |
Tests if SO_REUSEADDR is enabled. |
int |
getSoTimeout() |
Retrieve setting for SO_TIMEOUT . 0 returns implies that the option is disabled (i.e., timeout of infinity). |
protected final void |
implAccept |
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 |
Sets the value of a socket option. |
void |
setPerformancePreferences |
Sets performance preferences for this ServerSocket. |
void |
setReceiveBufferSize |
Sets a default proposed value for the SO_RCVBUF option for sockets accepted from this ServerSocket . |
void |
setReuseAddress |
Enable/disable the SO_REUSEADDR socket option. |
static void |
setSocketFactory |
Deprecated. |
void |
setSoTimeout |
Enable/disable SO_TIMEOUT with the specified timeout, in milliseconds. |
Set |
supportedOptions() |
Returns a set of the socket options supported by this server socket. |
String |
toString() |
Returns the implementation address and implementation port of this socket as a String . |
protected ServerSocket(SocketImpl impl)
SocketImpl
.impl
- an instance of a SocketImpl to use on the ServerSocket.NullPointerException
- if impl is null
.SecurityException
- if a security manager is set and its checkPermission
method doesn't allow NetPermission("setSocketImpl")
.public ServerSocket() throws IOException
IOException
- IO error when opening the socket.public ServerSocket(int port) throws IOException
0
means that the port number is automatically allocated, typically from an ephemeral port range. This port number can then be retrieved by calling getLocalPort
. 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.
If there is a security manager, its checkListen
method is called with the port
argument as its argument to ensure the operation is allowed. This could result in a SecurityException.
port
- the port number, or 0
to use a port number that is automatically allocated.IOException
- if an I/O error occurs when opening the socket.SecurityException
- if a security manager exists and its checkListen
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.public ServerSocket(int port, int backlog) throws IOException
0
means that the port number is automatically allocated, typically from an ephemeral port range. This port number can then be retrieved by calling getLocalPort
. 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.
If there is a security manager, its checkListen
method is called with the port
argument as its argument to ensure the operation is allowed. This could result in a SecurityException. 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 than 0
. If it is less than or equal to 0
, then an implementation specific default will be used.
port
- the port number, or 0
to use a port number that is automatically allocated.backlog
- requested maximum length of the queue of incoming connections.IOException
- if an I/O error occurs when opening the socket.SecurityException
- if a security manager exists and its checkListen
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.public ServerSocket(int port, int backlog, InetAddress bindAddr) throws IOException
0
means that the port number is automatically allocated, typically from an ephemeral port range. This port number can then be retrieved by calling getLocalPort
. If there is a security manager, this method calls its checkListen
method with the port
argument as its argument to ensure the operation is allowed. This could result in a SecurityException. 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 than 0
. If it is less than or equal to 0
, then an implementation specific default will be used.
port
- the port number, or 0
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 toSecurityException
- if a security manager exists and its checkListen
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.public void bind(SocketAddress endpoint) throws IOException
ServerSocket
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.
endpoint
- The IP address and port number to bind to.IOException
- if the bind operation fails, or if the socket is already bound.SecurityException
- if a SecurityManager
is present and its checkListen
method doesn't allow the operation.IllegalArgumentException
- if endpoint is a SocketAddress subclass not supported by this socketpublic void bind(SocketAddress endpoint, int backlog) throws IOException
ServerSocket
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 than 0
. If it is less than or equal to 0
, then an implementation specific default will be used.
endpoint
- The IP address and port number to bind to.backlog
- requested maximum length of the queue of incoming connections.IOException
- if the bind operation fails, or if the socket is already bound.SecurityException
- if a SecurityManager
is present and its checkListen
method doesn't allow the operation.IllegalArgumentException
- if endpoint is a SocketAddress subclass not supported by this socketpublic InetAddress getInetAddress()
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 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.
null
if the socket is unbound.public int getLocalPort()
If the socket was bound prior to being closed
, then this method will continue to return the port number after the socket is closed.
public SocketAddress getLocalSocketAddress()
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 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 the socket is bound is returned.
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.public Socket accept() throws IOException
This method is interruptible in the following circumstances:
ServerSocketChannel
. In that case, interrupting a thread accepting a connection will close the underlying channel and cause this method to throw ClosedByInterruptException
with the interrupt status set. SocketException
with the interrupt status set. A new Socket s
is created and, if there is a security manager, the security manager's checkAccept
method is called with s.getInetAddress().getHostAddress()
and s.getPort()
as its arguments to ensure the operation is allowed. This could result in a SecurityException.
SocketImpl
accepts sockets with a SocketImpl
of the same type, regardless of the client socket implementation factory, if one has been set.IOException
- if an I/O error occurs when waiting for a connection.SecurityException
- if a security manager exists and its checkAccept
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 acceptedprotected final void implAccept(Socket s) throws IOException
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 a SocketImpl
of a completely different type.
SocketImpl
can accept a connection with a Socket using a SocketImpl
of the same type: IOException
is thrown if the Socket is using a custom SocketImpl
. An instance of this class using a custom SocketImpl
cannot accept a connection with a Socket using a system-default SocketImpl
.s
- the SocketIllegalBlockingModeException
- 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 socketpublic void close() throws IOException
accept()
will throw a SocketException
. If this socket has an associated channel then the channel is closed as well.
close
in interface AutoCloseable
close
in interface Closeable
IOException
- if an I/O error occurs when closing the socket.public ServerSocketChannel getChannel()
ServerSocketChannel
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.
null
if this socket was not created for a channelpublic boolean isBound()
If the socket was bound prior to being closed, then this method will continue to return true
after the socket is closed.
public boolean isClosed()
public void setSoTimeout(int timeout) throws SocketException
SO_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, 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.timeout
- the specified timeout, in millisecondsSocketException
- if there is an error in the underlying protocol, such as a TCP errorIllegalArgumentException
- if timeout
is negativepublic int getSoTimeout() throws IOException
SO_TIMEOUT
. 0 returns implies that the option is disabled (i.e., timeout of infinity).SO_TIMEOUT
valueIOException
- if an I/O error occurspublic void setReuseAddress(boolean on) throws SocketException
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 ServerSocket
is created the initial setting of SO_REUSEADDR
is not defined. Applications can use getReuseAddress()
to determine the initial setting of SO_REUSEADDR
.
The behaviour when SO_REUSEADDR
is enabled or disabled after a socket is bound (See isBound()
) is not defined.
on
- whether to enable or disable the socket optionSocketException
- if an error occurs enabling or disabling the SO_REUSEADDR
socket option, or the socket is closed.public boolean getReuseAddress() throws SocketException
SO_REUSEADDR
is enabled.boolean
indicating whether or not SO_REUSEADDR
is enabled.SocketException
- if there is an error in the underlying protocol, such as a TCP error.public String toString()
String
. If there is a security manager set, and this socket is bound, 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, an InetAddress
representing the loopback
address is returned as the implementation address.
@Deprecated(since="17") public static void setSocketFactory(SocketImplFactory fac) throws IOException
ServerSocketFactory
and subclass ServerSocket
directly. ServerSocket
. It has been mostly obsolete since Java 1.4. If required, a ServerSocket
can be created to use a custom implementation by extending ServerSocket
and using the protected constructor that takes an implementation as a parameter. 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.
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.
fac
- the desired factory.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 checkSetFactory
method doesn't allow the operation.public void setReceiveBufferSize(int size) throws SocketException
SO_RCVBUF
option for sockets accepted from this ServerSocket
. The value actually set in the accepted socket must be determined by calling Socket.getReceiveBufferSize()
after the socket is returned by accept()
. 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.
size
- the size to which to set the receive buffer size. This value must be greater than 0.SocketException
- if there is an error in the underlying protocol, such as a TCP error.IllegalArgumentException
- if the value is 0 or is negative.public int getReceiveBufferSize() throws SocketException
SO_RCVBUF
option for this ServerSocket
, that is the proposed buffer size that will be used for Sockets accepted from this ServerSocket
. Note, the value actually set in the accepted socket is determined by calling Socket.getReceiveBufferSize()
.
SO_RCVBUF
option for this Socket
.SocketException
- if there is an error in the underlying protocol, such as a TCP error.public void setPerformancePreferences(int connectionTime, int latency, int bandwidth)
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.
connectionTime
- An int
expressing the relative importance of a short connection timelatency
- An int
expressing the relative importance of low latencybandwidth
- An int
expressing the relative importance of high bandwidthpublic <T> ServerSocket setOption(SocketOption<T> name, T value) throws IOException
T
- The type of the socket option valuename
- The socket optionvalue
- The value of the socket option. A value of null
may be valid for some options.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. StandardSocketOptions
do not require any security permission.public <T> T getOption(SocketOption<T> name) throws IOException
T
- The type of the socket option valuename
- The socket optionUnsupportedOperationException
- 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. StandardSocketOptions
do not require any security permission.public Set<SocketOption<?>> supportedOptions()
© 1993, 2023, Oracle and/or its affiliates. All rights reserved.
Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.
https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/net/ServerSocket.html
ServerSocketFactory
and subclassServerSocket
directly.