Java Doc for SocketChannel.java in  » 6.0-JDK-Core » io-nio » java » nio » channels » Java Source Code / Java DocumentationJava Source Code and Java Documentation

Socket channels are not a complete abstraction of connecting network sockets. Binding, shutdown, and the manipulation of socket options must be done through an associated java.net.Socket object obtained by invoking the SocketChannel.socket() socket method. It is not possible to create a channel for an arbitrary, pre-existing socket, nor is it possible to specify the java.net.SocketImpl object to be used by a socket associated with a socket channel.

A socket channel is created by invoking one of the SocketChannel.open open methods of this class. A newly-created socket channel is open but not yet connected. An attempt to invoke an I/O operation upon an unconnected channel will cause a NotYetConnectedException to be thrown. A socket channel can be connected by invoking its SocketChannel.connect connect method; once connected, a socket channel remains connected until it is closed. Whether or not a socket channel is connected may be determined by invoking its SocketChannel.isConnected isConnected method.

Socket channels support non-blocking connection: A socket channel may be created and the process of establishing the link to the remote socket may be initiated via the SocketChannel.connect connect method for later completion by the SocketChannel.finishConnect finishConnect method. Whether or not a connection operation is in progress may be determined by invoking the SocketChannel.isConnectionPending isConnectionPending method.

The input and output sides of a socket channel may independently be shut down without actually closing the channel. Shutting down the input side of a channel by invoking the java.net.Socket.shutdownInputshutdownInput method of an associated socket object will cause further reads on the channel to return -1, the end-of-stream indication. Shutting down the output side of the channel by invoking the java.net.Socket.shutdownOutput shutdownOutput method of an associated socket object will cause further writes on the channel to throw a ClosedChannelException .

Socket channels support asynchronous shutdown, which is similar to the asynchronous close operation specified in the Channel class. If the input side of a socket is shut down by one thread while another thread is blocked in a read operation on the socket's channel, then the read operation in the blocked thread will complete without reading any bytes and will return -1. If the output side of a socket is shut down by one thread while another thread is blocked in a write operation on the socket's channel, then the blocked thread will receive an AsynchronousCloseException .

Socket channels are safe for use by multiple concurrent threads. They support concurrent reading and writing, though at most one thread may be reading and at most one thread may be writing at any given time. The SocketChannel.connect connect and SocketChannel.finishConnect finishConnect methods are mutually synchronized against each other, and an attempt to initiate a read or write operation while an invocation of one of these methods is in progress will block until that invocation is complete.

If this channel is in non-blocking mode then an invocation of this method initiates a non-blocking connection operation.

A non-blocking connection operation is initiated by placing a socket channel in non-blocking mode and then invoking its SocketChannel.connectconnect method.

The new channel is created by invoking the java.nio.channels.spi.SelectorProvider.openSocketChannelopenSocketChannel method of the system-wide default java.nio.channels.spi.SelectorProvider object.

This convenience method works as if by invoking the SocketChannel.open() method, invoking the SocketChannel.connect(SocketAddress) connect method upon the resulting socket channel, passing it remote, and then returning that channel.

The returned object will not declare any public methods that are not declared in the java.net.Socket class.

Socket channels support connecting, reading, and writing, so this method returns ( SelectionKey.OP_CONNECT |  SelectionKey.OP_READ |  SelectionKey.OP_WRITE ).

If this channel is in non-blocking mode then an invocation of this method initiates a non-blocking connection operation. If the connection is established immediately, as can happen with a local connection, then this method returns true. Otherwise this method returns false and the connection operation must later be completed by invoking the SocketChannel.finishConnect finishConnect method.

If this channel is in blocking mode then an invocation of this method will block until the connection is established or an I/O error occurs.

This method performs exactly the same security checks as the java.net.Socket class. That is, if a security manager has been installed then this method verifies that its java.lang.SecurityManager.checkConnect checkConnect method permits connecting to the address and port number of the given remote endpoint.

This method may be invoked at any time. If a read or write operation upon this channel is invoked while an invocation of this method is in progress then that operation will first block until this invocation is complete. If a connection attempt is initiated but fails, that is, if an invocation of this method throws a checked exception, then the channel will be closed.

A non-blocking connection operation is initiated by placing a socket channel in non-blocking mode and then invoking its SocketChannel.connectconnect method. Once the connection is established, or the attempt has failed, the socket channel will become connectable and this method may be invoked to complete the connection sequence. If the connection operation failed then invoking this method will cause an appropriate java.io.IOException to be thrown.

If this channel is already connected then this method will not block and will immediately return true. If this channel is in non-blocking mode then this method will return false if the connection process is not yet complete. If this channel is in blocking mode then this method will block until the connection either completes or fails, and will always either return true or throw a checked exception describing the failure.

This method may be invoked at any time. If a read or write operation upon this channel is invoked while an invocation of this method is in progress then that operation will first block until this invocation is complete. If a connection attempt fails, that is, if an invocation of this method throws a checked exception, then the channel will be closed.

The new channel is created by invoking the java.nio.channels.spi.SelectorProvider.openSocketChannelopenSocketChannel method of the system-wide default java.nio.channels.spi.SelectorProvider object.

This convenience method works as if by invoking the SocketChannel.open() method, invoking the SocketChannel.connect(SocketAddress) connect method upon the resulting socket channel, passing it remote, and then returning that channel.

The returned object will not declare any public methods that are not declared in the java.net.Socket class.

Socket channels support connecting, reading, and writing, so this method returns ( SelectionKey.OP_CONNECT |  SelectionKey.OP_READ |  SelectionKey.OP_WRITE ).