java.net
class ServerSocket

java.lang.Object java.net.ServerSocket

Direct Known Subclasses:

SSLServerSocket

Most common way to construct:

int port = …;

ServerSocket server = new ServerSocket(port);

Based on 166 examples

public class ServerSocket
extends Object

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.

See Also (auto-generated):

Thread

Socket

Integer

ServerSocket

public ServerSocket()
             throws IOException

Creates an unbound server socket.

Throws:

IOException - IO error when opening the socket.

ServerSocket

public ServerSocket(int port)
             throws IOException

Creates a server socket, bound to the specified port. A port of 0 creates a socket on any free port.

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 - the port number, or 0 to use any free port.

Throws:

IOException - if an I/O error occurs when opening the socket.

ServerSocket

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 creates a socket on any free port.

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 must be a positive value greater than 0. If the value passed if equal or less than 0, then the default value will be assumed.

Parameters:

port - the specified port, or 0 to use any free port.

backlog - the maximum length of the queue.

Throws:

IOException - if an I/O error occurs when opening the socket.

ServerSocket

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.

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 must be a positive value greater than 0. If the value passed if equal or less than 0, then the default value will be assumed.

Parameters:

port - the local TCP port

backlog - the listen backlog

bindAddr - the local InetAddress the server will bind to

Throws:

IOException - if an I/O error occurs when opening the socket.

accept

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.

Returns:

the new Socket

Throws:

IOException - if an I/O error occurs when waiting for a connection.

bind

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.

Parameters:

endpoint - The IP address & port number to bind to.

Throws:

IOException - if the bind operation fails, or if the socket is already bound.

bind

public 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 must be a positive value greater than 0. If the value passed if equal or less than 0, then the default value will be assumed.

Parameters:

endpoint - The IP address & port number to bind to.

backlog - The listen backlog length.

Throws:

IOException - if the bind operation fails, or if the socket is already bound.

close

public void close()
           throws IOException

Closes this socket. Any thread currently blocked in {@link #accept()} will throw a {@link 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 {@link 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 {@link java.nio.channels.ServerSocketChannel#open ServerSocketChannel.open} method.

Returns:

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.

Returns:

the address to which this socket is bound, or null if the socket is unbound.

getLocalPort

public int getLocalPort()

Returns the port on which this socket is listening.

Returns:

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, or null if it is not bound yet.

Returns:

a SocketAddress representing the local endpoint of this socket, or null if it is not bound yet.

getReceiveBufferSize

public synchronized 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 {@link Socket#getReceiveBufferSize()}.

Returns:

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.

getReuseAddress

public boolean getReuseAddress()
                        throws SocketException

Tests if SO_REUSEADDR is enabled.

Returns:

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.

getSoTimeout

public synchronized int getSoTimeout()
                              throws IOException

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

Returns:

the SO_TIMEOUT value

Throws:

IOException - if an I/O error occurs

implAccept

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.

Parameters:

s - the Socket

Throws:

IOException - if an I/O error occurs when waiting for a connection.

isBound

public boolean isBound()

Returns the binding state of the ServerSocket.

Returns:

true if the ServerSocket succesfuly bound to an address

isClosed

public boolean isClosed()

Returns the closed state of the ServerSocket.

Returns:

true if the socket has been closed

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 - An int expressing the relative importance of a short connection time

latency - An int expressing the relative importance of low latency

bandwidth - An int expressing the relative importance of high bandwidth

setReceiveBufferSize

public synchronized 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 {@link Socket#getReceiveBufferSize()} after the socket is returned by {@link #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 {@link 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 - 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.

setReuseAddress

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 {@link #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 {@link #getReuseAddress()} to determine the initial setting of SO_REUSEADDR.

The behaviour when SO_REUSEADDR is enabled or disabled after a socket is bound (See {@link #isBound()}) is not defined.

Parameters:

on - whether to enable or disable the socket option

Throws:

SocketException - if an error occurs enabling or disabling the SO_RESUEADDR socket option, or the socket is closed.

setSocketFactory

public static synchronized 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.

Parameters:

fac - the desired factory.

Throws:

IOException - if an I/O error occurs when setting the socket factory.

setSoTimeout

public synchronized 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.

Parameters:

timeout - the specified timeout, in milliseconds

Throws:

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

toString

public String toString()

Returns the implementation address and implementation port of this socket as a String.

Overrides:

toString in class Object

Returns:

a string representation of this socket.