SocketChannel (More New I/O APIs for the Java™ Platform)

java.lang.Object
- java.nio.channels.spi.AbstractInterruptibleChannel
- - java.nio.channels.SelectableChannel
  - - java.nio.channels.spi.AbstractSelectableChannel
    - - java.nio.channels.SocketChannel

All Implemented Interfaces:: Closeable, AutoCloseable, ByteChannel, Channel, GatheringByteChannel, InterruptibleChannel, NetworkChannel, ReadableByteChannel, ScatteringByteChannel, WritableByteChannel

public abstract class SocketChannel
extends AbstractSelectableChannel
implements ByteChannel, ScatteringByteChannel, GatheringByteChannel, NetworkChannel

A selectable channel for stream-oriented connecting sockets.

A socket channel is created by invoking one of the open methods of this class. It is not possible to create a channel for an arbitrary, pre-existing socket. 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 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 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 connect method for later completion by the finishConnect method. Whether or not a connection operation is in progress may be determined by invoking the isConnectionPending method.

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 options are configured using the setOption method. Socket channels support the following options:

Option Name Description

SO_SNDBUF The size of the socket send buffer

SO_RCVBUF The size of the socket receive buffer

SO_KEEPALIVE Keep connection alive

SO_REUSEADDR Re-use address

SO_LINGER Linger on close if data is present (when configured in blocking mode only)

TCP_NODELAY Disable the Nagle algorithm

Option Name	Description
`SO_SNDBUF`	The size of the socket send buffer
`SO_RCVBUF`	The size of the socket receive buffer
`SO_KEEPALIVE`	Keep connection alive
`SO_REUSEADDR`	Re-use address
`SO_LINGER`	Linger on close if data is present (when configured in blocking mode only)
`TCP_NODELAY`	Disable the Nagle algorithm

Additional (implementation specific) options may also be supported.

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 connect and 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.

Since:: 1.4

Constructor Summary

Constructors
Modifier Constructor and Description

protected SocketChannel(SelectorProvider provider)
Initializes a new instance of this class.

Constructors
Modifier	Constructor and Description
`protected`	`SocketChannel(SelectorProvider provider)` Initializes a new instance of this class.

Method Summary

Methods
Modifier and Type	Method and Description
`abstract SocketChannel`	`bind(SocketAddress local)` Binds the channel's socket to a local address.
`abstract boolean`	`connect(SocketAddress remote)` Connects this channel's socket.
`abstract boolean`	`finishConnect()` Finishes the process of connecting a socket channel.
`abstract SocketAddress`	`getRemoteAddress()` Returns the remote address to which this channel's socket is connected.
`abstract boolean`	`isConnected()` Tells whether or not this channel's network socket is connected.
`abstract boolean`	`isConnectionPending()` Tells whether or not a connection operation is in progress on this channel.
`static SocketChannel`	`open()` Opens a socket channel.
`static SocketChannel`	`open(SocketAddress remote)` Opens a socket channel and connects it to a remote address.
`abstract int`	`read(ByteBuffer dst)`
`long`	`read(ByteBuffer[] dsts)`
`abstract long`	`read(ByteBuffer[] dsts, int offset, int length)`
`abstract <T> SocketChannel`	`setOption(SocketOption<T> name, T value)` Sets the value of a socket option.
`abstract SocketChannel`	`shutdownInput()` Shutdown the connection for reading without closing the channel.
`abstract SocketChannel`	`shutdownOutput()` Shutdown the connection for writing without closing the channel.
`abstract Socket`	`socket()` Retrieves a socket associated with this channel.
`int`	`validOps()` Returns an operation set identifying this channel's supported operations.
`abstract int`	`write(ByteBuffer src)`
`long`	`write(ByteBuffer[] srcs)`
`abstract long`	`write(ByteBuffer[] srcs, int offset, int length)`

Methods inherited from class java.nio.channels.spi.AbstractSelectableChannel
blockingLock, configureBlocking, implCloseChannel, implCloseSelectableChannel, implConfigureBlocking, isBlocking, isRegistered, keyFor, provider, register

Methods inherited from class java.nio.channels.SelectableChannel
register

Methods inherited from class java.nio.channels.spi.AbstractInterruptibleChannel
begin, close, end, isOpen

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface java.nio.channels.Channel
close, isOpen

Methods inherited from interface java.nio.channels.NetworkChannel
getLocalAddress, getOption, supportedOptions

- Constructor Detail
  - SocketChannel
```
protected SocketChannel(SelectorProvider provider)
```
    Initializes a new instance of this class.
- Method Detail
  - open
```
public static SocketChannel open()
                          throws IOException
```
    Opens a socket channel.
    The new channel is created by invoking the openSocketChannel method of the system-wide default SelectorProvider object.
    
    Returns:
    A new socket channel
    
    Throws:
    
    IOException - If an I/O error occurs
  - open
```
public static SocketChannel open(SocketAddress remote)
                          throws IOException
```
    Opens a socket channel and connects it to a remote address.
    This convenience method works as if by invoking the open() method, invoking the connect method upon the resulting socket channel, passing it remote, and then returning that channel.
    
    Parameters:
    remote - The remote address to which the new channel is to be connected
    
    Throws:
    
    AsynchronousCloseException - If another thread closes this channel while the connect operation is in progress
    
    ClosedByInterruptException - If another thread interrupts the current thread while the connect operation is in progress, thereby closing the channel and setting the current thread's interrupt status
    
    UnresolvedAddressException - If the given remote address is not fully resolved
    
    UnsupportedAddressTypeException - If the type of the given remote address is not supported
    
    SecurityException - If a security manager has been installed and it does not permit access to the given remote endpoint
    
    IOException - If some other I/O error occurs
  - validOps
```
public final int validOps()
```
    Returns an operation set identifying this channel's supported operations.
    Socket channels support connecting, reading, and writing, so this method returns (SelectionKey.OP_CONNECT | SelectionKey.OP_READ | SelectionKey.OP_WRITE).
    
    Specified by:
    
    validOps in class SelectableChannel
    
    Returns:
    The valid-operation set
  - bind
```
public abstract SocketChannel bind(SocketAddress local)
                            throws IOException
```
    Description copied from interface: NetworkChannel
    
    Binds the channel's socket to a local address.
    This method is used to establish an association between the socket and a local address. Once an association is established then the socket remains bound until the channel is closed. If the local parameter has the value null then the socket will be bound to an address that is assigned automatically.
    
    Specified by:
    
    bind in interface NetworkChannel
    
    Parameters:
    local - The address to bind the socket, or null to bind the socket to an automatically assigned socket address
    
    Returns:
    This channel
    
    Throws:
    
    ConnectionPendingException - If a non-blocking connect operation is already in progress on this channel
    
    AlreadyBoundException - If the socket is already bound
    
    UnsupportedAddressTypeException - If the type of the given address is not supported
    
    ClosedChannelException - If the channel is closed
    
    IOException - If some other I/O error occurs
    Since:
    
    1.7
    
    See Also:
    NetworkChannel.getLocalAddress()
  - setOption
```
public abstract <T> SocketChannel setOption(SocketOption<T> name,
                          T value)
                                 throws IOException
```
    Description copied from interface: NetworkChannel
    
    Sets the value of a socket option.
    
    Specified by:
    
    setOption in interface NetworkChannel
    
    Parameters:
    name - The socket option
    value - The value of the socket option. A value of null may be a valid value for some socket options.
    
    Returns:
    This channel
    
    Throws:
    
    UnsupportedOperationException - If the socket option is not supported by this channel
    
    IllegalArgumentException - If the value is not a valid value for this socket option
    
    ClosedChannelException - If this channel is closed
    
    IOException - If an I/O error occurs
    Since:
    
    1.7
    
    See Also:
    StandardSocketOption
  - shutdownInput
```
public abstract SocketChannel shutdownInput()
                                     throws IOException
```
    Shutdown the connection for reading without closing the channel.
    Once shutdown for reading then further reads on the channel will return -1, the end-of-stream indication. If the input side of the connection is already shutdown then invoking this method has no effect.
    
    Returns:
    The channel
    
    Throws:
    
    NotYetConnectedException - If this channel is not yet connected
    
    ClosedChannelException - If this channel is closed
    
    IOException - If some other I/O error occurs
    Since:
    
    1.7
  - shutdownOutput
```
public abstract SocketChannel shutdownOutput()
                                      throws IOException
```
    Shutdown the connection for writing without closing the channel.
    Once shutdown for writing then further attempts to write to the channel will throw ClosedChannelException. If the output side of the connection is already shutdown then invoking this method has no effect.
    
    Returns:
    The channel
    
    Throws:
    
    NotYetConnectedException - If this channel is not yet connected
    
    ClosedChannelException - If this channel is closed
    
    IOException - If some other I/O error occurs
    Since:
    
    1.7
  - socket
```
public abstract Socket socket()
```
    Retrieves a socket associated with this channel.
    The returned object will not declare any public methods that are not declared in the Socket class.
    
    Returns:
    A socket associated with this channel
  - isConnected
```
public abstract boolean isConnected()
```
    Tells whether or not this channel's network socket is connected.
    
    Returns:
    true if, and only if, this channel's network socket is open and connected
  - isConnectionPending
```
public abstract boolean isConnectionPending()
```
    Tells whether or not a connection operation is in progress on this channel.
    
    Returns:
    true if, and only if, a connection operation has been initiated on this channel but not yet completed by invoking the finishConnect method
  - connect
```
public abstract boolean connect(SocketAddress remote)
                         throws IOException
```
    Connects this channel's socket.
    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 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 Socket class. That is, if a security manager has been installed then this method verifies that its 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.
    
    Parameters:
    remote - The remote address to which this channel is to be connected
    
    Returns:
    true if a connection was established, false if this channel is in non-blocking mode and the connection operation is in progress
    
    Throws:
    
    AlreadyConnectedException - If this channel is already connected
    
    ConnectionPendingException - If a non-blocking connection operation is already in progress on this channel
    
    ClosedChannelException - If this channel is closed
    
    AsynchronousCloseException - If another thread closes this channel while the connect operation is in progress
    
    ClosedByInterruptException - If another thread interrupts the current thread while the connect operation is in progress, thereby closing the channel and setting the current thread's interrupt status
    
    UnresolvedAddressException - If the given remote address is not fully resolved
    
    UnsupportedAddressTypeException - If the type of the given remote address is not supported
    
    SecurityException - If a security manager has been installed and it does not permit access to the given remote endpoint
    
    IOException - If some other I/O error occurs
  - finishConnect
```
public abstract boolean finishConnect()
                               throws IOException
```
    Finishes the process of connecting a socket channel.
    A non-blocking connection operation is initiated by placing a socket channel in non-blocking mode and then invoking its connect 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 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.
    
    Returns:
    true if, and only if, this channel's socket is now connected
    
    Throws:
    
    NoConnectionPendingException - If this channel is not connected and a connection operation has not been initiated
    
    ClosedChannelException - If this channel is closed
    
    AsynchronousCloseException - If another thread closes this channel while the connect operation is in progress
    
    ClosedByInterruptException - If another thread interrupts the current thread while the connect operation is in progress, thereby closing the channel and setting the current thread's interrupt status
    
    IOException - If some other I/O error occurs
  - getRemoteAddress
```
public abstract SocketAddress getRemoteAddress()
                                        throws IOException
```
    Returns the remote address to which this channel's socket is connected.
    Where the channel is bound and connected to an Internet Protocol socket address then the return value from this method is of type InetSocketAddress.
    
    Returns:
    The remote address; null if the channel's socket is not connected
    
    Throws:
    
    ClosedChannelException - If the channel is closed
    
    IOException - If an I/O error occurs
    Since:
    
    1.7
  - read
```
public abstract int read(ByteBuffer dst)
                  throws IOException
```
    Specified by:
    
    read in interface ReadableByteChannel
    
    Throws:
    
    NotYetConnectedException - If this channel is not yet connected
    
    IOException
  - read
```
public abstract long read(ByteBuffer[] dsts,
        int offset,
        int length)
                   throws IOException
```
    Specified by:
    
    read in interface ScatteringByteChannel
    
    Throws:
    
    NotYetConnectedException - If this channel is not yet connected
    
    IOException
  - read
```
public final long read(ByteBuffer[] dsts)
                throws IOException
```
    Specified by:
    
    read in interface ScatteringByteChannel
    
    Throws:
    
    NotYetConnectedException - If this channel is not yet connected
    
    IOException
  - write
```
public abstract int write(ByteBuffer src)
                   throws IOException
```
    Specified by:
    
    write in interface WritableByteChannel
    
    Throws:
    
    NotYetConnectedException - If this channel is not yet connected
    
    IOException
  - write
```
public abstract long write(ByteBuffer[] srcs,
         int offset,
         int length)
                    throws IOException
```
    Specified by:
    
    write in interface GatheringByteChannel
    
    Throws:
    
    NotYetConnectedException - If this channel is not yet connected
    
    IOException
  - write
```
public final long write(ByteBuffer[] srcs)
                 throws IOException
```
    Specified by:
    
    write in interface GatheringByteChannel
    
    Throws:
    
    NotYetConnectedException - If this channel is not yet connected
    
    IOException

Class SocketChannel

Constructor Summary

Method Summary

Methods inherited from class java.nio.channels.spi.AbstractSelectableChannel

Methods inherited from class java.nio.channels.SelectableChannel

Methods inherited from class java.nio.channels.spi.AbstractInterruptibleChannel

Methods inherited from class java.lang.Object

Methods inherited from interface java.nio.channels.Channel

Methods inherited from interface java.nio.channels.NetworkChannel

Constructor Detail

SocketChannel

Method Detail

open

open

validOps

bind

setOption

shutdownInput

shutdownOutput

socket

isConnected

isConnectionPending

connect

finishConnect

getRemoteAddress

read

read

read

write

write

write