ServerSocket
public
class
ServerSocket
extends Object
implements
Closeable
java.lang.Object | |
↳ | java.net.ServerSocket |
|
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 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.
Summary
Public constructors | |
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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. |
Public methods | |
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Socket
|
accept()
Listens for a connection to be made to this socket and accepts it. |
void
|
bind(SocketAddress endpoint, int backlog)
Binds the |
void
|
bind(SocketAddress endpoint)
Binds the |
void
|
close()
Closes this socket. |
ServerSocketChannel
|
getChannel()
Returns the unique |
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(SocketOption<T> name)
Returns the value of a socket option. |
int
|
getReceiveBufferSize()
Gets the value of the |
boolean
|
getReuseAddress()
Tests if |
int
|
getSoTimeout()
Retrieve setting for |
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 the
|
void
|
setReuseAddress(boolean on)
Enable/disable the |
void
|
setSoTimeout(int timeout)
Enable/disable |
static
void
|
setSocketFactory(SocketImplFactory fac)
Sets the server socket implementation factory for the application. |
Set<SocketOption<?>>
|
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 |
Protected methods | |
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final
void
|
implAccept(Socket s)
Subclasses of ServerSocket use this method to override accept() to return their own subclass of socket. |
Inherited methods | |||||||||||||||||||||||
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Public constructors
ServerSocket
public ServerSocket ()
Creates an unbound server socket.
Throws | |
---|---|
IOException |
IO error when opening the socket. |
ServerSocket
public ServerSocket (int port)
Creates a server socket, bound to the specified port. A port number
of 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.
Parameters | |
---|---|
port |
int : the port number, or 0 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 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. |
ServerSocket
public ServerSocket (int port, int backlog)
Creates a server socket and binds it to the specified local port
number, with the specified backlog.
A port number of 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.
Parameters | |
---|---|
port |
int : the port number, or 0 to use a port
number that is automatically allocated. |
backlog |
int : 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 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. |
ServerSocket
public ServerSocket (int port, int backlog, InetAddress bindAddr)
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 of 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.
Parameters | |
---|---|
port |
int : the port number, or 0 to use a port
number that is automatically allocated. |
backlog |
int : requested maximum length of the queue of incoming
connections. |
bindAddr |
InetAddress : the local InetAddress the server will bind to |
Throws | |
---|---|
SecurityException |
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 methods
accept
public Socket accept ()
Listens for a connection to be made to this socket and accepts it. The method blocks until a connection is made.
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.
Returns | |
---|---|
Socket |
the new Socket |
Throws | |
---|---|
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 accepted |
See also:
bind
public void bind (SocketAddress endpoint, int backlog)
Binds the 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.
Parameters | |
---|---|
endpoint |
SocketAddress : The IP address and port number to bind to. |
backlog |
int : 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 SecurityManager is present and
its checkListen method doesn't allow the operation. |
IllegalArgumentException |
if endpoint is a SocketAddress subclass not supported by this socket |
bind
public void bind (SocketAddress endpoint)
Binds the 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.
Parameters | |
---|---|
endpoint |
SocketAddress : 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 SecurityManager is present and
its checkListen method doesn't allow the operation. |
IllegalArgumentException |
if endpoint is a SocketAddress subclass not supported by this socket |
close
public void close ()
Closes this socket.
Any thread currently blocked in accept()
will throw
a SocketException
.
If this socket has an associated channel then the channel is closed as well.
Throws | |
---|---|
IOException |
if an I/O error occurs when closing the socket. |
getChannel
public ServerSocketChannel getChannel ()
Returns the unique 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.
Returns | |
---|---|
ServerSocketChannel |
the server-socket channel associated with this socket,
or null if this socket was not created
for a channel |
getInetAddress
public InetAddress 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.
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.
Returns | |
---|---|
InetAddress |
the address to which this socket is bound,
or the loopback address if denied by the security manager,
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 | |
---|---|
int |
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 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.
Returns | |
---|---|
SocketAddress |
a 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. |
getOption
public T getOption (SocketOption<T> name)
Returns the value of a socket option.
Parameters | |
---|---|
name |
SocketOption : The socket option |
Returns | |
---|---|
T |
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.
StandardSocketOptions
do not require any security permission. |
getReceiveBufferSize
public 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
.
Note, the value actually set in the accepted socket is determined by
calling Socket#getReceiveBufferSize()
.
Returns | |
---|---|
int |
the value of the SO_RCVBUF
option for this Socket . |
Throws | |
---|---|
SocketException |
if there is an error in the underlying protocol, such as a TCP error. |
See also:
getReuseAddress
public boolean getReuseAddress ()
Tests if SO_REUSEADDR
is enabled.
Returns | |
---|---|
boolean |
a boolean indicating whether or not
SO_REUSEADDR is enabled. |
Throws | |
---|---|
SocketException |
if there is an error in the underlying protocol, such as a TCP error. |
See also:
getSoTimeout
public int getSoTimeout ()
Retrieve setting for SO_TIMEOUT
.
0 returns implies that the option is disabled (i.e., timeout of infinity).
Returns | |
---|---|
int |
the SO_TIMEOUT value |
Throws | |
---|---|
IOException |
if an I/O error occurs |
See also:
isBound
public boolean isBound ()
Returns the binding state of the ServerSocket.
Returns | |
---|---|
boolean |
true if the ServerSocket successfully bound to an address |
isClosed
public boolean isClosed ()
Returns the closed state of the ServerSocket.
Returns | |
---|---|
boolean |
true if the socket has been closed |
setOption
public ServerSocket setOption (SocketOption<T> name, T value)
Sets the value of a socket option.
Parameters | |
---|---|
name |
SocketOption : The socket option |
value |
T : The value of the socket option. A value of null
may be valid for some options. |
Returns | |
---|---|
ServerSocket |
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.
StandardSocketOptions
do not require any security permission. |
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 |
int : An int expressing the relative importance of a short
connection time |
latency |
int : An int expressing the relative importance of low
latency |
bandwidth |
int : An int expressing the relative importance of high
bandwidth |
setReceiveBufferSize
public void setReceiveBufferSize (int size)
Sets a default proposed value for the
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 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.
Parameters | |
---|---|
size |
int : 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. |
See also:
setReuseAddress
public void setReuseAddress (boolean on)
Enable/disable the 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(java.net.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.
Parameters | |
---|---|
on |
boolean : whether to enable or disable the socket option |
Throws | |
---|---|
SocketException |
if an error occurs enabling or
disabling the SO_REUSEADDR
socket option, or the socket is closed. |
setSoTimeout
public void setSoTimeout (int timeout)
Enable/disable SO_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,
a java.net.SocketTimeoutException is raised, though the
ServerSocket is still valid. The option must 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 |
int : the specified timeout, in milliseconds |
Throws | |
---|---|
SocketException |
if there is an error in the underlying protocol, such as a TCP error. |
See also:
setSocketFactory
public static void setSocketFactory (SocketImplFactory fac)
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.
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.
Parameters | |
---|---|
fac |
SocketImplFactory : 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
checkSetFactory method doesn't allow the operation. |
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 | |
---|---|
Set<SocketOption<?>> |
A set of the socket options supported by this socket. This set may be empty if the socket's SocketImpl cannot be created. |
toString
public String toString ()
Returns the implementation address and implementation port of
this socket as a String
.
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,
an InetAddress
representing the
loopback
address is returned as
the implementation address.
Returns | |
---|---|
String |
a string representation of this socket. |
Protected methods
implAccept
protected final void implAccept (Socket s)
Subclasses of ServerSocket use this method to override accept() to return their own subclass of socket. So a FooServerSocket will typically hand this method an empty FooSocket. On return from implAccept the FooSocket will be connected to a client.
Parameters | |
---|---|
s |
Socket : 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. |