public class ServerSocket extends Object implements Closeable
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.
SocketImpl
, setSocketFactory(java.net.SocketImplFactory)
, ServerSocketChannel
public ServerSocket() throws IOException
Creates an unbound server socket.
IOException
- IO error when opening the socket.public ServerSocket(int port) throws IOException
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.
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
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.
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
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.
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
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.
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
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.
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()
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.
null
if the socket is unbound.SecurityManager.checkConnect(java.lang.String, int)
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.
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.
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.getInetAddress()
, getLocalPort()
, bind(SocketAddress)
, SecurityManager.checkConnect(java.lang.String, int)
public Socket accept() throws IOException
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.
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
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.
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
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.
close
in interface Closeable
close
in interface AutoCloseable
IOException
- if an I/O error occurs when closing the socket.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.
null
if this socket was not created for a channelpublic boolean isBound()
Returns the binding state of the ServerSocket.
public boolean isClosed()
Returns the closed state of the ServerSocket.
public void setSoTimeout(int timeout) throws SocketException
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.
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
Retrieve setting for SO_TIMEOUT
. 0 returns implies that the option is disabled (i.e., timeout of infinity).
SO_TIMEOUT
valueIOException
- if an I/O error occurssetSoTimeout(int)
public void setReuseAddress(boolean on) throws SocketException
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(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.getReuseAddress()
, bind(SocketAddress)
, isBound()
, isClosed()
public boolean getReuseAddress() throws SocketException
Tests if 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.setReuseAddress(boolean)
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.
public static void setSocketFactory(SocketImplFactory fac) throws IOException
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.
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
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.
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
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()
.
SO_RCVBUF
option for this Socket
.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)
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.
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
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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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