Added in API level 1

ServerSocket

open class ServerSocket : Closeable

kotlin.Any
↳	java.net.ServerSocket

Known Direct Subclasses SSLServerSocket SSLServerSocket This class extends ServerSockets and provides secure server sockets using protocols such as the Secure Sockets Layer (SSL) or Transport Layer Security (TLS) protocols.

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
ServerSocket() Creates an unbound server socket.
ServerSocket(port: Int) Creates a server socket, bound to the specified port.
ServerSocket(port: Int, backlog: Int) Creates a server socket and binds it to the specified local port number, with the specified backlog.
ServerSocket(port: Int, backlog: Int, bindAddr: InetAddress!) Create a server with the specified port, listen backlog, and local IP address to bind to.

Public methods
open Socket!	accept() Listens for a connection to be made to this socket and accepts it.
open Unit	bind(endpoint: SocketAddress!) Binds the ServerSocket to a specific address (IP address and port number).
open Unit	bind(endpoint: SocketAddress!, backlog: Int) Binds the ServerSocket to a specific address (IP address and port number).
open Unit	close() Closes this socket.
open ServerSocketChannel!	getChannel() Returns the unique java.nio.channels.ServerSocketChannel object associated with this socket, if any.
open InetAddress!	getInetAddress() Returns the local address of this server socket.
open Int	getLocalPort() Returns the port number on which this socket is listening.
open SocketAddress!	getLocalSocketAddress() Returns the address of the endpoint this socket is bound to.
open T	getOption(name: SocketOption<T>!) Returns the value of a socket option.
open 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.
open Boolean	getReuseAddress() Tests if SO_REUSEADDR is enabled.
open Int	getSoTimeout() Retrieve setting for SO_TIMEOUT.
open Boolean	isBound() Returns the binding state of the ServerSocket.
open Boolean	isClosed() Returns the closed state of the ServerSocket.
open ServerSocket!	setOption(name: SocketOption<T>!, value: T) Sets the value of a socket option.
open Unit	setPerformancePreferences(connectionTime: Int, latency: Int, bandwidth: Int) Sets performance preferences for this ServerSocket.
open Unit	setReceiveBufferSize(size: Int) Sets a default proposed value for the SO_RCVBUF option for sockets accepted from this ServerSocket.
open Unit	setReuseAddress(on: Boolean) Enable/disable the SO_REUSEADDR socket option.
open Unit	setSoTimeout(timeout: Int) Enable/disable SO_TIMEOUT with the specified timeout, in milliseconds.
open static Unit	setSocketFactory(fac: SocketImplFactory!) Sets the server socket implementation factory for the application.
open MutableSet<SocketOption<*>!>!	supportedOptions() Returns a set of the socket options supported by this server socket.
open String	toString() Returns the implementation address and implementation port of this socket as a String.

Protected methods
Unit	implAccept(s: Socket!) Subclasses of ServerSocket use this method to override accept() to return their own subclass of socket.

Public constructors

ServerSocket

Added in API level 1

ServerSocket()

Creates an unbound server socket.

Exceptions
java.io.IOException	IO error when opening the socket.

ServerSocket

Added in API level 1

ServerSocket(port: Int)

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.

Exceptions
java.io.IOException	if an I/O error occurs when opening the socket.
java.lang.SecurityException	if a security manager exists and its checkListen method doesn't allow the operation.
java.lang.IllegalArgumentException	if the port parameter is outside the specified range of valid port values, which is between 0 and 65535, inclusive.

See Also

• java.net.SocketImpl
• java.net.SocketImplFactory#createSocketImpl()
• java.net.ServerSocket#setSocketFactory(java.net.SocketImplFactory)
• java.lang.SecurityManager#checkListen

ServerSocket

Added in API level 1

ServerSocket(
    port: Int, 
    backlog: Int)

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.

Exceptions
java.io.IOException	if an I/O error occurs when opening the socket.
java.lang.SecurityException	if a security manager exists and its checkListen method doesn't allow the operation.
java.lang.IllegalArgumentException	if the port parameter is outside the specified range of valid port values, which is between 0 and 65535, inclusive.

See Also

• java.net.SocketImpl
• java.net.SocketImplFactory#createSocketImpl()
• java.net.ServerSocket#setSocketFactory(java.net.SocketImplFactory)
• java.lang.SecurityManager#checkListen

ServerSocket

Added in API level 1

ServerSocket(
    port: Int, 
    backlog: Int, 
    bindAddr: InetAddress!)

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

Exceptions
java.lang.SecurityException	if a security manager exists and its checkListen method doesn't allow the operation.
java.io.IOException	if an I/O error occurs when opening the socket.
java.lang.IllegalArgumentException	if the port parameter is outside the specified range of valid port values, which is between 0 and 65535, inclusive.

See Also

• java.net.SocketOptions
• java.net.SocketImpl
• java.lang.SecurityManager#checkListen

Public methods

accept

Added in API level 1

open fun accept(): Socket!

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.

Return
Socket!	the new Socket

Exceptions
java.io.IOException	if an I/O error occurs when waiting for a connection.
java.lang.SecurityException	if a security manager exists and its checkAccept method doesn't allow the operation.
java.net.SocketTimeoutException	if a timeout was previously set with setSoTimeout and the timeout has been reached.
java.nio.channels.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

• java.lang.SecurityManager#checkAccept

bind

Added in API level 1

open fun bind(endpoint: SocketAddress!): Unit

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.

Exceptions
java.io.IOException	if the bind operation fails, or if the socket is already bound.
java.lang.SecurityException	if a SecurityManager is present and its checkListen method doesn't allow the operation.
java.lang.IllegalArgumentException	if endpoint is a SocketAddress subclass not supported by this socket

bind

Added in API level 1

open fun bind(
    endpoint: SocketAddress!, 
    backlog: Int
): Unit

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.

Exceptions
java.io.IOException	if the bind operation fails, or if the socket is already bound.
java.lang.SecurityException	if a SecurityManager is present and its checkListen method doesn't allow the operation.
java.lang.IllegalArgumentException	if endpoint is a SocketAddress subclass not supported by this socket

close

Added in API level 1

open fun close(): Unit

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.

Exceptions
java.lang.Exception	if this resource cannot be closed
java.io.IOException	if an I/O error occurs
java.io.IOException	if an I/O error occurs when closing the socket.

getChannel

Added in API level 1

open fun getChannel(): ServerSocketChannel!

Returns the unique java.nio.channels.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.

Return
ServerSocketChannel!	the server-socket channel associated with this socket, or null if this socket was not created for a channel

getInetAddress

Added in API level 1

open fun getInetAddress(): InetAddress!

Returns the local address of this server socket.

If the socket was bound prior to being #close, 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.

Return
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.

See Also

getLocalPort

Added in API level 1

open fun getLocalPort(): Int

Returns the port number on which this socket is listening.

If the socket was bound prior to being #close, then this method will continue to return the port number after the socket is closed.

Return
Int	the port number to which this socket is listening or -1 if the socket is not bound yet.

getLocalSocketAddress

Added in API level 1

open fun getLocalSocketAddress(): SocketAddress!

Returns the address of the endpoint this socket is bound to.

If the socket was bound prior to being #close, 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.

Return
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.

See Also

• #getInetAddress()
• #getLocalPort()
• #bind(SocketAddress)

getOption

Added in API level 33

open fun <T : Any!> getOption(name: SocketOption<T>!): T

Returns the value of a socket option.

Parameters
<T>	The type of the socket option value
name	SocketOption<T>!: The socket option

Return
T	The value of the socket option.

Exceptions
java.lang.UnsupportedOperationException	if the server socket does not support the option.
java.io.IOException	if an I/O error occurs, or if the socket is closed.
java.lang.NullPointerException	if name is null
java.lang.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

Added in API level 1

open fun getReceiveBufferSize(): Int

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().

Return
Int	the value of the SO_RCVBUF option for this Socket.

Exceptions
java.net.SocketException	if there is an error in the underlying protocol, such as a TCP error.

See Also

• #setReceiveBufferSize(int)

getReuseAddress

Added in API level 1

open fun getReuseAddress(): Boolean

Tests if SO_REUSEADDR is enabled.

Return
Boolean	a boolean indicating whether or not SO_REUSEADDR is enabled.

Exceptions
java.net.SocketException	if there is an error in the underlying protocol, such as a TCP error.

See Also

• #setReuseAddress(boolean)

getSoTimeout

Added in API level 1

open fun getSoTimeout(): Int

Retrieve setting for SO_TIMEOUT. 0 returns implies that the option is disabled (i.e., timeout of infinity).

Return
Int	the SO_TIMEOUT value

Exceptions
java.io.IOException	if an I/O error occurs

See Also

• #setSoTimeout(int)

isBound

Added in API level 1

open fun isBound(): Boolean

Returns the binding state of the ServerSocket.

Return
Boolean	true if the ServerSocket successfully bound to an address

isClosed

Added in API level 1

open fun isClosed(): Boolean

Returns the closed state of the ServerSocket.

Return
Boolean	true if the socket has been closed

setOption

Added in API level 33

open fun <T : Any!> setOption(
    name: SocketOption<T>!, 
    value: T
): ServerSocket!

Sets the value of a socket option.

Parameters
<T>	The type of the socket option value
name	SocketOption<T>!: The socket option
value	T: The value of the socket option. A value of null may be valid for some options.

Return
ServerSocket!	this ServerSocket

Exceptions
java.lang.UnsupportedOperationException	if the server socket does not support the option.
java.lang.IllegalArgumentException	if the value is not valid for the option.
java.io.IOException	if an I/O error occurs, or if the socket is closed.
java.lang.NullPointerException	if name is null
java.lang.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

Added in API level 1

open fun setPerformancePreferences(
    connectionTime: Int, 
    latency: Int, 
    bandwidth: Int
): Unit

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

Added in API level 1

open fun setReceiveBufferSize(size: Int): Unit

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.

Exceptions
java.net.SocketException	if there is an error in the underlying protocol, such as a TCP error.
java.lang.IllegalArgumentException	if the value is 0 or is negative.

See Also

• #getReceiveBufferSize

setReuseAddress

Added in API level 1

open fun setReuseAddress(on: Boolean): Unit

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

Exceptions
java.net.SocketException	if an error occurs enabling or disabling the SO_REUSEADDR socket option, or the socket is closed.

See Also

• #getReuseAddress()
• #bind(SocketAddress)
• #isBound()
• #isClosed()

setSoTimeout

Added in API level 1

open fun setSoTimeout(timeout: Int): Unit

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

Exceptions
java.net.SocketException	if there is an error in the underlying protocol, such as a TCP error.

See Also

• #getSoTimeout()

setSocketFactory

Added in API level 1

open static fun setSocketFactory(fac: SocketImplFactory!): Unit

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.

Exceptions
java.io.IOException	if an I/O error occurs when setting the socket factory.
java.net.SocketException	if the factory has already been defined.
java.lang.SecurityException	if a security manager exists and its checkSetFactory method doesn't allow the operation.

See Also

• java.net.SocketImplFactory#createSocketImpl()
• java.lang.SecurityManager#checkSetFactory

supportedOptions

Added in API level 33

open fun supportedOptions(): MutableSet<SocketOption<*>!>!

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.

Return
MutableSet<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

Added in API level 1

open fun toString(): String

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.

Return
String	a string representation of this socket.

Protected methods

implAccept

Added in API level 1

protected fun implAccept(s: Socket!): Unit

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

Exceptions
java.nio.channels.IllegalBlockingModeException	if this socket has an associated channel, and the channel is in non-blocking mode
java.io.IOException	if an I/O error occurs when waiting for a connection.