AsynchronousServerSocketChannel (Java SE 23 & JDK 23)
Description: declaration: module: java.base, package: java.nio.channels, class: AsynchronousServerSocketChannel
Keywords: java.nio.channels.AsynchronousServerSocketChannel class

# Class AsynchronousServerSocketChannel

java.lang.Object
java.nio.channels.AsynchronousServerSocketChannel

All Implemented Interfaces:
  `Closeable`, `AutoCloseable`, `AsynchronousChannel`, `Channel`, `NetworkChannel`

public abstract class AsynchronousServerSocketChannel extends Object implements AsynchronousChannel, NetworkChannel
An asynchronous channel for stream-oriented listening sockets.

An asynchronous server-socket channel is created by invoking the `open` method of this class. A newly-created asynchronous server-socket channel is open but not yet bound. It can be bound to a local address and configured to listen for connections by invoking the `bind` method. Once bound, the `accept` method is used to initiate the accepting of connections to the channel's socket. An attempt to invoke the `accept` method on an unbound channel will cause a `NotYetBoundException` to be thrown.

Channels of this type are safe for use by multiple concurrent threads though at most one accept operation can be outstanding at any time. If a thread initiates an accept operation before a previous accept operation has completed then an `AcceptPendingException` will be thrown.

Socket options are configured using the `setOption` method. Channels of this type support the following options:

> Socket options
> Option Name | Description
> --- | ---
> `SO_RCVBUF` | The size of the socket receive buffer
> `SO_REUSEADDR` | Re-use address

Additional (implementation specific) options may also be supported.

Usage Example:

     final AsynchronousServerSocketChannel listener =
         AsynchronousServerSocketChannel.open().bind(new InetSocketAddress(5000));

     listener.accept(null, new CompletionHandler<AsynchronousSocketChannel,Void>() {
         public void completed(AsynchronousSocketChannel ch, Void att) {
             // accept the next connection
             listener.accept(null, this);

             // handle this connection
             handle(ch);
         }
         public void failed(Throwable exc, Void att) {
             ...
         }
     });

Since:
  1.7

- ## Constructor Summary

  Constructors
  Modifier
  Constructor
  Description
  `protected`
  `AsynchronousServerSocketChannel(AsynchronousChannelProvider provider)`
  Initializes a new instance of this class.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `abstract Future<AsynchronousSocketChannel>`
  `accept()`
  Accepts a connection.
  `abstract <A> void`
  `accept(A attachment, CompletionHandler<AsynchronousSocketChannel,? super A> handler)`
  Accepts a connection.
  `final AsynchronousServerSocketChannel`
  `bind(SocketAddress local)`
  Binds the channel's socket to a local address and configures the socket to listen for connections.
  `abstract AsynchronousServerSocketChannel`
  `bind(SocketAddress local, int backlog)`
  Binds the channel's socket to a local address and configures the socket to listen for connections.
  `abstract SocketAddress`
  `getLocalAddress()`
  Returns the socket address that this channel's socket is bound to.
  `static AsynchronousServerSocketChannel`
  `open()`
  Opens an asynchronous server-socket channel.
  `static AsynchronousServerSocketChannel`
  `open(AsynchronousChannelGroup group)`
  Opens an asynchronous server-socket channel.
  `final AsynchronousChannelProvider`
  `provider()`
  Returns the provider that created this channel.
  `abstract <T> AsynchronousServerSocketChannel`
  `setOption(SocketOption<T> name, T value)`
  Sets the value of a socket option.

  ### Methods declared in class java.lang.Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

  ### Methods declared in interface java.nio.channels.AsynchronousChannel

  `close`

  ### Methods declared in interface java.nio.channels.Channel

  `isOpen`

  ### Methods declared in interface java.nio.channels.NetworkChannel

  `getOption, supportedOptions`

- ## Constructor Details

  - ### AsynchronousServerSocketChannel

    protected AsynchronousServerSocketChannel(AsynchronousChannelProvider provider)
    Initializes a new instance of this class.
    Parameters:
      `provider` - The provider that created this channel

- ## Method Details

  - ### provider

    public final AsynchronousChannelProvider provider()
    Returns the provider that created this channel.
    Returns:
      The provider that created this channel

  - ### open

    public static AsynchronousServerSocketChannel open(AsynchronousChannelGroup group) throws IOException
    Opens an asynchronous server-socket channel.

    The new channel is created by invoking the `openAsynchronousServerSocketChannel` method on the `AsynchronousChannelProvider` object that created the given group. If the group parameter is `null` then the resulting channel is created by the system-wide default provider, and bound to the default group.

    Parameters:
      `group` - The group to which the newly constructed channel should be bound, or `null` for the default group
    Returns:
      A new asynchronous server socket channel
    Throws:
      `ShutdownChannelGroupException` - If the channel group is shutdown
      `IOException` - If an I/O error occurs

  - ### open

    public static AsynchronousServerSocketChannel open() throws IOException
    Opens an asynchronous server-socket channel.

    This method returns an asynchronous server socket channel that is bound to the default group. This method is equivalent to evaluating the expression:

            open((AsynchronousChannelGroup)null);

    Returns:
      A new asynchronous server socket channel
    Throws:
      `IOException` - If an I/O error occurs

  - ### bind

    public final AsynchronousServerSocketChannel bind(SocketAddress local) throws IOException
    Binds the channel's socket to a local address and configures the socket to listen for connections.

    An invocation of this method is equivalent to the following:

            bind(local, 0);

    Specified by:
      `bind` in interface `NetworkChannel`
    Parameters:
      `local` - The local address to bind the socket, or `null` to bind to an automatically assigned socket address
    Returns:
      This channel
    Throws:
      `AlreadyBoundException` - If the socket is already bound
      `UnsupportedAddressTypeException` - If the type of the given address is not supported
      `SecurityException` - If a security manager is installed and it denies an unspecified permission. An implementation of this interface should specify any required permissions.
      `ClosedChannelException` - If the channel is closed
      `IOException` - If some other I/O error occurs
    See Also:
      - `NetworkChannel.getLocalAddress()`

  - ### bind

    public abstract AsynchronousServerSocketChannel bind(SocketAddress local, int backlog) throws IOException
    Binds the channel's socket to a local address and configures the socket to listen for connections.

    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 associated channel is closed.

    The `backlog` parameter is the 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. If the `backlog` parameter has the value `0`, or a negative value, then an implementation specific default is used.

    Parameters:
      `local` - The local address to bind the socket, or `null` to bind to an automatically assigned socket address
      `backlog` - The maximum number of pending connections
    Returns:
      This channel
    Throws:
      `AlreadyBoundException` - If the socket is already bound
      `UnsupportedAddressTypeException` - If the type of the given address is not supported
      `SecurityException` - If a security manager has been installed and its `checkListen` method denies the operation
      `ClosedChannelException` - If the channel is closed
      `IOException` - If some other I/O error occurs

  - ### setOption

    public abstract <T> AsynchronousServerSocketChannel 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`
    Type Parameters:
      `T` - The type of the socket option value
    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:
      `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
    See Also:
      - `StandardSocketOptions`

  - ### accept

    public abstract <A> void accept(A attachment, CompletionHandler<AsynchronousSocketChannel,? super A> handler)
    Accepts a connection.

    This method initiates an asynchronous operation to accept a connection made to this channel's socket. The `handler` parameter is a completion handler that is invoked when a connection is accepted (or the operation fails). The result passed to the completion handler is the `AsynchronousSocketChannel` to the new connection.

    When a new connection is accepted then the resulting `AsynchronousSocketChannel` will be bound to the same `AsynchronousChannelGroup` as this channel. If the group is `shutdown` and a connection is accepted, then the connection is closed, and the operation completes with an `IOException` and cause `ShutdownChannelGroupException`.

    To allow for concurrent handling of new connections, the completion handler is not invoked directly by the initiating thread when a new connection is accepted immediately (see Threading).

    If a security manager has been installed then it verifies that the address and port number of the connection's remote endpoint are permitted by the security manager's `checkAccept` method. The permission check is performed with privileges that are restricted by the calling context of this method. If the permission check fails then the connection is closed and the operation completes with a `SecurityException`.

    Type Parameters:
      `A` - The type of the attachment
    Parameters:
      `attachment` - The object to attach to the I/O operation; can be `null`
      `handler` - The handler for consuming the result
    Throws:
      `AcceptPendingException` - If an accept operation is already in progress on this channel
      `NotYetBoundException` - If this channel's socket has not yet been bound
      `ShutdownChannelGroupException` - If the channel group has terminated

  - ### accept

    public abstract Future<AsynchronousSocketChannel> accept()
    Accepts a connection.

    This method initiates an asynchronous operation to accept a connection made to this channel's socket. The method behaves in exactly the same manner as the `accept(Object, CompletionHandler)` method except that instead of specifying a completion handler, this method returns a `Future` representing the pending result. The `Future`'s `get` method returns the `AsynchronousSocketChannel` to the new connection on successful completion.

    Returns:
      a `Future` object representing the pending result
    Throws:
      `AcceptPendingException` - If an accept operation is already in progress on this channel
      `NotYetBoundException` - If this channel's socket has not yet been bound

  - ### getLocalAddress

    public abstract SocketAddress getLocalAddress() throws IOException
    Returns the socket address that this channel's socket is bound to.

    Where the channel is `bound` to an Internet Protocol socket address then the return value from this method is of type `InetSocketAddress`.

    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 of the channel's socket is returned.

    Specified by:
      `getLocalAddress` in interface `NetworkChannel`
    Returns:
      The `SocketAddress` that the socket is bound to, or the `SocketAddress` representing the loopback address if denied by the security manager, or `null` if the channel's socket is not bound
    Throws:
      `ClosedChannelException` - If the channel is closed
      `IOException` - If an I/O error occurs