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ServerSocket.javaAPI DocJava SE 6 API28979Tue Jun 10 00:25:42 BST 2008java.net

ServerSocket

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.

author
unascribed
version
1.91, 03/08/07
see
java.net.SocketImpl
see
java.net.ServerSocket#setSocketFactory(java.net.SocketImplFactory)
see
java.nio.channels.ServerSocketChannel
since
JDK1.0

Fields Summary
private boolean
created
Various states of this socket.
private boolean
bound
private boolean
closed
private Object
closeLock
private SocketImpl
impl
The implementation of this Socket.
private boolean
oldImpl
Are we using an older SocketImpl?
private static SocketImplFactory
factory
The factory for all server sockets.
Constructors Summary
public ServerSocket()
Creates an unbound server socket.

exception
IOException IO error when opening the socket.
revised
1.4


                        
        
	setImpl();
    
public ServerSocket(int port)
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.

param
port the port number, or 0 to use any free port.
exception
IOException if an I/O error occurs when opening the socket.
exception
SecurityException if a security manager exists and its checkListen method doesn't allow the operation.
see
java.net.SocketImpl
see
java.net.SocketImplFactory#createSocketImpl()
see
java.net.ServerSocket#setSocketFactory(java.net.SocketImplFactory)
see
SecurityManager#checkListen

	this(port, 50, null);
    
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 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.

param
port the specified port, or 0 to use any free port.
param
backlog the maximum length of the queue.
exception
IOException if an I/O error occurs when opening the socket.
exception
SecurityException if a security manager exists and its checkListen method doesn't allow the operation.
see
java.net.SocketImpl
see
java.net.SocketImplFactory#createSocketImpl()
see
java.net.ServerSocket#setSocketFactory(java.net.SocketImplFactory)
see
SecurityManager#checkListen

	this(port, backlog, null);
    
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.

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.

param
port the local TCP port
param
backlog the listen backlog
param
bindAddr the local InetAddress the server will bind to
throws
SecurityException if a security manager exists and its checkListen method doesn't allow the operation.
throws
IOException if an I/O error occurs when opening the socket.
see
SocketOptions
see
SocketImpl
see
SecurityManager#checkListen
since
JDK1.1

	setImpl();
	if (port < 0 || port > 0xFFFF)
	    throw new IllegalArgumentException(
		       "Port value out of range: " + port);
	if (backlog < 1)
	  backlog = 50;
	try {
	    bind(new InetSocketAddress(bindAddr, port), backlog);
	} catch(SecurityException e) {
	    close();
	    throw e;
	} catch(IOException e) {
	    close();
	    throw e;
	}
    
Methods Summary
public java.net.Socketaccept()
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.

exception
IOException if an I/O error occurs when waiting for a connection.
exception
SecurityException if a security manager exists and its checkAccept method doesn't allow the operation.
exception
SocketTimeoutException if a timeout was previously set with setSoTimeout and the timeout has been reached.
exception
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
return
the new Socket
see
SecurityManager#checkAccept
revised
1.4
spec
JSR-51

	if (isClosed())
	    throw new SocketException("Socket is closed");
	if (!isBound())
	    throw new SocketException("Socket is not bound yet");
	Socket s = new Socket((SocketImpl) null);
	implAccept(s);
	return s;
    
public voidbind(java.net.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 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.

param
endpoint The IP address & port number to bind to.
param
backlog The listen backlog length.
throws
IOException if the bind operation fails, or if the socket is already bound.
throws
SecurityException if a SecurityManager is present and its checkListen method doesn't allow the operation.
throws
IllegalArgumentException if endpoint is a SocketAddress subclass not supported by this socket
since
1.4

	if (isClosed())
	    throw new SocketException("Socket is closed");
	if (!oldImpl && isBound())
	    throw new SocketException("Already bound");
	if (endpoint == null)
	    endpoint = new InetSocketAddress(0);
	if (!(endpoint instanceof InetSocketAddress))
	    throw new IllegalArgumentException("Unsupported address type");
	InetSocketAddress epoint = (InetSocketAddress) endpoint;
	if (epoint.isUnresolved())
	    throw new SocketException("Unresolved address");
	if (backlog < 1)
	  backlog = 50;
	try {
	    SecurityManager security = System.getSecurityManager();
	    if (security != null)
		security.checkListen(epoint.getPort());
	    getImpl().bind(epoint.getAddress(), epoint.getPort());
	    getImpl().listen(backlog);
	    bound = true;
	} catch(SecurityException e) {
	    bound = false;
	    throw e;
	} catch(IOException e) {
	    bound = false;
	    throw e;
	}
    
public voidbind(java.net.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.

param
endpoint The IP address & port number to bind to.
throws
IOException if the bind operation fails, or if the socket is already bound.
throws
SecurityException if a SecurityManager is present and its checkListen method doesn't allow the operation.
throws
IllegalArgumentException if endpoint is a SocketAddress subclass not supported by this socket
since
1.4

	bind(endpoint, 50);
    
private voidcheckOldImpl()

	if (impl == null)
	    return;
	// SocketImpl.connect() is a protected method, therefore we need to use
	// getDeclaredMethod, therefore we need permission to access the member
	try {
	    AccessController.doPrivileged(new PrivilegedExceptionAction() {
		    public Object run() throws NoSuchMethodException {
			Class[] cl = new Class[2];
			cl[0] = SocketAddress.class;
			cl[1] = Integer.TYPE;
			impl.getClass().getDeclaredMethod("connect", cl);
			return null;
		    }
		});
	} catch (java.security.PrivilegedActionException e) {
	    oldImpl = true;
	}
    
public voidclose()
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.

exception
IOException if an I/O error occurs when closing the socket.
revised
1.4
spec
JSR-51

	synchronized(closeLock) {
	    if (isClosed())
		return;
	    if (created)
		impl.close();
	    closed = true;
	}
    
voidcreateImpl()
Creates the socket implementation.

throws
IOException if creation fails
since
1.4

	if (impl == null)
	    setImpl();
	try {
	    impl.create(true);
	    created = true;
	} catch (IOException e) {
	    throw new SocketException(e.getMessage());
	}
    
public java.nio.channels.ServerSocketChannelgetChannel()
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.

return
the server-socket channel associated with this socket, or null if this socket was not created for a channel
since
1.4
spec
JSR-51

	return null;
    
java.net.SocketImplgetImpl()
Get the SocketImpl attached to this socket, creating it if necessary.

return
the SocketImpl attached to that ServerSocket.
throws
SocketException if creation fails.
since
1.4

	if (!created)
	    createImpl();
	return impl;
    
public java.net.InetAddressgetInetAddress()
Returns the local address of this server socket.

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

	if (!isBound())
	    return null;
	try {
	    return getImpl().getInetAddress();
	} catch (SocketException e) {
	    // nothing
	    // If we're bound, the impl has been created
	    // so we shouldn't get here
	}
	return null;
    
public intgetLocalPort()
Returns the port on which this socket is listening.

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

	if (!isBound())
	    return -1;
	try {
	    return getImpl().getLocalPort();
	} catch (SocketException e) {
	    // nothing
	    // If we're bound, the impl has been created
	    // so we shouldn't get here
	}
	return -1;
    
public java.net.SocketAddressgetLocalSocketAddress()
Returns the address of the endpoint this socket is bound to, or null if it is not bound yet.

return
a SocketAddress representing the local endpoint of this socket, or null if it is not bound yet.
see
#getInetAddress()
see
#getLocalPort()
see
#bind(SocketAddress)
since
1.4

	if (!isBound())
	    return null;
	return new InetSocketAddress(getInetAddress(), getLocalPort());
    
public synchronized intgetReceiveBufferSize()
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()}.

return
the value of the SO_RCVBUF option for this Socket.
exception
SocketException if there is an error in the underlying protocol, such as a TCP error.
see
#setReceiveBufferSize(int)
since
1.4

	if (isClosed())
	    throw new SocketException("Socket is closed");
	int result = 0;
	Object o = getImpl().getOption(SocketOptions.SO_RCVBUF);
	if (o instanceof Integer) {
	    result = ((Integer)o).intValue();
	}
	return result;
    
public booleangetReuseAddress()
Tests if SO_REUSEADDR is enabled.

return
a boolean indicating whether or not SO_REUSEADDR is enabled.
exception
SocketException if there is an error in the underlying protocol, such as a TCP error.
since
1.4
see
#setReuseAddress(boolean)

	if (isClosed())
	    throw new SocketException("Socket is closed");
	return ((Boolean) (getImpl().getOption(SocketOptions.SO_REUSEADDR))).booleanValue();
    
public synchronized intgetSoTimeout()
Retrieve setting for SO_TIMEOUT. 0 returns implies that the option is disabled (i.e., timeout of infinity).

return
the SO_TIMEOUT value
exception
IOException if an I/O error occurs
since
JDK1.1
see
#setSoTimeout(int)

	if (isClosed())
	    throw new SocketException("Socket is closed");
	Object o = getImpl().getOption(SocketOptions.SO_TIMEOUT);
	/* extra type safety */
	if (o instanceof Integer) {
	    return ((Integer) o).intValue();
	} else {
	    return 0;
	}
    
protected final voidimplAccept(java.net.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.

param
s the Socket
throws
java.nio.channels.IllegalBlockingModeException if this socket has an associated channel, and the channel is in non-blocking mode
throws
IOException if an I/O error occurs when waiting for a connection.
since
JDK1.1
revised
1.4
spec
JSR-51

	SocketImpl si = null;
	try {
	    if (s.impl == null)
	      s.setImpl();
            else {
                s.impl.reset();
            }
	    si = s.impl;	    
	    s.impl = null;
	    si.address = new InetAddress();
	    si.fd = new FileDescriptor();
	    getImpl().accept(si);
 	    
	    SecurityManager security = System.getSecurityManager();
	    if (security != null) {
		security.checkAccept(si.getInetAddress().getHostAddress(),
				     si.getPort());
	    }
	} catch (IOException e) {
	    if (si != null)
		si.reset();
            s.impl = si;
	    throw e;
	} catch (SecurityException e) {
	    if (si != null)
		si.reset();
	    s.impl = si;
	    throw e;
	}
	s.impl = si;
	s.postAccept();
    
public booleanisBound()
Returns the binding state of the ServerSocket.

return
true if the ServerSocket succesfuly bound to an address
since
1.4

	// Before 1.3 ServerSockets were always bound during creation
	return bound || oldImpl;
    
public booleanisClosed()
Returns the closed state of the ServerSocket.

return
true if the socket has been closed
since
1.4

	synchronized(closeLock) {
	    return closed;
	}
    
voidsetBound()

	bound = true;
    
voidsetCreated()

	created = true;
    
private voidsetImpl()

	if (factory != null) {
	    impl = factory.createSocketImpl();
	    checkOldImpl();
	} else {
	    // No need to do a checkOldImpl() here, we know it's an up to date
	    // SocketImpl!
	    impl = new SocksSocketImpl();
	}
	if (impl != null)
	    impl.setServerSocket(this);
    
public voidsetPerformancePreferences(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.

param
connectionTime An int expressing the relative importance of a short connection time
param
latency An int expressing the relative importance of low latency
param
bandwidth An int expressing the relative importance of high bandwidth
since
1.5

	/* Not implemented yet */
    
public synchronized voidsetReceiveBufferSize(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 {@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.

exception
SocketException if there is an error in the underlying protocol, such as a TCP error.
param
size the size to which to set the receive buffer size. This value must be greater than 0.
exception
IllegalArgumentException if the value is 0 or is negative.
since
1.4
see
#getReceiveBufferSize

	if (!(size > 0)) {
	    throw new IllegalArgumentException("negative receive size");
	}
	if (isClosed())
	    throw new SocketException("Socket is closed");
	getImpl().setOption(SocketOptions.SO_RCVBUF, new Integer(size));
    
public voidsetReuseAddress(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 {@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.

param
on whether to enable or disable the socket option
exception
SocketException if an error occurs enabling or disabling the SO_RESUEADDR socket option, or the socket is closed.
since
1.4
see
#getReuseAddress()
see
#bind(SocketAddress)
see
#isBound()
see
#isClosed()

	if (isClosed())
	    throw new SocketException("Socket is closed");
        getImpl().setOption(SocketOptions.SO_REUSEADDR, Boolean.valueOf(on));
    
public synchronized voidsetSoTimeout(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.

param
timeout the specified timeout, in milliseconds
exception
SocketException if there is an error in the underlying protocol, such as a TCP error.
since
JDK1.1
see
#getSoTimeout()

	if (isClosed())
	    throw new SocketException("Socket is closed");
	getImpl().setOption(SocketOptions.SO_TIMEOUT, new Integer(timeout));
    
public static synchronized voidsetSocketFactory(java.net.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.

param
fac the desired factory.
exception
IOException if an I/O error occurs when setting the socket factory.
exception
SocketException if the factory has already been defined.
exception
SecurityException if a security manager exists and its checkSetFactory method doesn't allow the operation.
see
java.net.SocketImplFactory#createSocketImpl()
see
SecurityManager#checkSetFactory


                                                                                                                                                                                                      
            
	if (factory != null) {
	    throw new SocketException("factory already defined");
	}
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    security.checkSetFactory();
	}
	factory = fac;
    
public java.lang.StringtoString()
Returns the implementation address and implementation port of this socket as a String.

return
a string representation of this socket.

	if (!isBound())
	    return "ServerSocket[unbound]";
	return "ServerSocket[addr=" + impl.getInetAddress() + 
		",port=" + impl.getPort() + 
		",localport=" + impl.getLocalPort()  + "]";