public class ServerSocket extends Object implements Closeable
The actual work of the server socket is performed by an instance
of the SocketImpl
class. An application can
change the socket factory that creates the socket
implementation to configure itself to create sockets
appropriate to the local firewall.
SocketImpl
,
setSocketFactory(java.net.SocketImplFactory)
,
ServerSocketChannel
Constructor and Description |
---|
ServerSocket()
Creates 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.
|
Modifier and Type | Method and Description |
---|---|
Socket |
accept()
Listens for a connection to be made to this socket and accepts
it.
|
void |
bind(SocketAddress endpoint)
Binds the
ServerSocket to a specific address
(IP address and port number). |
void |
bind(SocketAddress endpoint,
int backlog)
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, or
null if it is not bound yet. |
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.
|
protected 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.
|
void |
setPerformancePreferences(int connectionTime,
int latency,
int bandwidth)
Sets performance preferences for this ServerSocket.
|
void |
setReceiveBufferSize(int size)
Sets a default proposed value for the SO_RCVBUF option for sockets
accepted from this ServerSocket.
|
void |
setReuseAddress(boolean on)
Enable/disable the SO_REUSEADDR socket option.
|
static void |
setSocketFactory(SocketImplFactory fac)
Sets the server socket implementation factory for the
application.
|
void |
setSoTimeout(int timeout)
Enable/disable SO_TIMEOUT with the specified timeout, in
milliseconds.
|
String |
toString()
Returns the implementation address and implementation port of
this socket as a
String . |
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 factory, that
factory's createSocketImpl
method is called to create
the actual socket implementation. Otherwise a "plain" socket 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.SocketImpl
,
SocketImplFactory.createSocketImpl()
,
setSocketFactory(java.net.SocketImplFactory)
,
SecurityManager.checkListen(int)
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 factory, that
factory's createSocketImpl
method is called to create
the actual socket implementation. Otherwise a "plain" socket 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 altogther. 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.SocketImpl
,
SocketImplFactory.createSocketImpl()
,
setSocketFactory(java.net.SocketImplFactory)
,
SecurityManager.checkListen(int)
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 altogther. 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.SocketOptions
,
SocketImpl
,
SecurityManager.checkListen(int)
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 & 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 altogther. 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 & 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.
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()
null
if it is not bound yet.
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.
SocketAddress
representing the local endpoint of this
socket, or null
if it is not bound yet.getInetAddress()
,
getLocalPort()
,
bind(SocketAddress)
public Socket accept() throws IOException
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.
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
acceptedSecurityManager.checkAccept(java.lang.String, int)
protected final void implAccept(Socket s) throws IOException
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.public 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 Closeable
close
in interface AutoCloseable
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.
public boolean isBound()
public boolean isClosed()
public void setSoTimeout(int timeout) throws SocketException
timeout
- the specified timeout, in millisecondsSocketException
- if there is an error in
the underlying protocol, such as a TCP error.getSoTimeout()
public int getSoTimeout() throws IOException
IOException
- if an I/O error occurssetSoTimeout(int)
public void setReuseAddress(boolean on) throws SocketException
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_RESUEADDR socket option,
or the socket is closed.getReuseAddress()
,
bind(SocketAddress)
,
isBound()
,
isClosed()
public boolean getReuseAddress() throws SocketException
boolean
indicating whether or not SO_REUSEADDR is enabled.SocketException
- if there is an error
in the underlying protocol, such as a TCP error.setReuseAddress(boolean)
public String toString()
String
.public static void setSocketFactory(SocketImplFactory fac) throws IOException
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.SocketImplFactory.createSocketImpl()
,
SecurityManager.checkSetFactory()
public void setReceiveBufferSize(int size) throws SocketException
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 advertized 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.getReceiveBufferSize()
public int getReceiveBufferSize() throws SocketException
Note, the value actually set in the accepted socket is determined by
calling Socket.getReceiveBufferSize()
.
SocketException
- if there is an error
in the underlying protocol, such as a TCP error.setReceiveBufferSize(int)
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
bandwidth Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
Copyright © 1993, 2020, Oracle and/or its affiliates. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.
Scripting on this page tracks web page traffic, but does not change the content in any way.