Java compact1, compact2, compact3 java.nio.channels Class AsynchronousFileChannel（JDK8）

Constructor Detail

• AsynchronousFileChannel

  protected AsynchronousFileChannel()

  Initializes a new instance of this class.

Method Detail

• open

  public static AsynchronousFileChannel open(Path file,
                                             Set<? extends OpenOption> options,
                                             ExecutorService executor,
                                             FileAttribute<?>... attrs)
                                      throws IOException

  Opens or creates a file for reading and/or writing, returning an asynchronous file channel to access the file.

  The options parameter determines how the file is opened. The READ and WRITE options determines if the file should be opened for reading and/or writing. If neither option is contained in the array then an existing file is opened for reading.

  In addition to READ and WRITE, the following options may be present:

  Option	Description
  TRUNCATE_EXISTING	When opening an existing file, the file is first truncated to a size of 0 bytes. This option is ignored when the file is opened only for reading.
  CREATE_NEW	If this option is present then a new file is created, failing if the file already exists. When creating a file the check for the existence of the file and the creation of the file if it does not exist is atomic with respect to other file system operations. This option is ignored when the file is opened only for reading.
  CREATE	If this option is present then an existing file is opened if it exists, otherwise a new file is created. When creating a file the check for the existence of the file and the creation of the file if it does not exist is atomic with respect to other file system operations. This option is ignored if the CREATE_NEW option is also present or the file is opened only for reading.
  DELETE_ON_CLOSE	When this option is present then the implementation makes a best effort attempt to delete the file when closed by the the close method. If the close method is not invoked then a best effort attempt is made to delete the file when the Java virtual machine terminates.
  SPARSE	When creating a new file this option is a hint that the new file will be sparse. This option is ignored when not creating a new file.
  SYNC	Requires that every update to the file's content or metadata be written synchronously to the underlying storage device. (see Synchronized I/O file integrity).
  DSYNC	Requires that every update to the file's content be written synchronously to the underlying storage device. (see Synchronized I/O file integrity).

  An implementation may also support additional options.

  The executor parameter is the ExecutorService to which tasks are submitted to handle I/O events and dispatch completion results for operations initiated on resulting channel. The nature of these tasks is highly implementation specific and so care should be taken when configuring the Executor. Minimally it should support an unbounded work queue and should not run tasks on the caller thread of the execute method. Shutting down the executor service while the channel is open results in unspecified behavior.

  The attrs parameter is an optional array of file file-attributes to set atomically when creating the file.

  The new channel is created by invoking the newFileChannel method on the provider that created the Path.

  Parameters:

  file - The path of the file to open or create

  options - Options specifying how the file is opened

  executor - The thread pool or null to associate the channel with the default thread pool

  attrs - An optional list of file attributes to set atomically when creating the file

  Returns:

  A new asynchronous file channel

  Throws:

  IllegalArgumentException - If the set contains an invalid combination of options

  UnsupportedOperationException - If the file is associated with a provider that does not support creating asynchronous file channels, or an unsupported open option is specified, or the array contains an attribute that cannot be set atomically when creating the file

  IOException - If an I/O error occurs

  SecurityException - If a security manager is installed and it denies an unspecified permission required by the implementation. In the case of the default provider, the SecurityManager.checkRead(String) method is invoked to check read access if the file is opened for reading. The SecurityManager.checkWrite(String) method is invoked to check write access if the file is opened for writing

• open

  public static AsynchronousFileChannel open(Path file,
                                             OpenOption... options)
                                      throws IOException

  Opens or creates a file for reading and/or writing, returning an asynchronous file channel to access the file.

  An invocation of this method behaves in exactly the same way as the invocation

       ch.open(file, opts, null, new FileAttribute<?>[0]);
   

  where opts is a Set containing the options specified to this method.

  The resulting channel is associated with default thread pool to which tasks are submitted to handle I/O events and dispatch to completion handlers that consume the result of asynchronous operations performed on the resulting channel.

  Parameters:

  file - The path of the file to open or create

  options - Options specifying how the file is opened

  Returns:

  A new asynchronous file channel

  Throws:

  IllegalArgumentException - If the set contains an invalid combination of options

  UnsupportedOperationException - If the file is associated with a provider that does not support creating file channels, or an unsupported open option is specified

  IOException - If an I/O error occurs

  SecurityException - If a security manager is installed and it denies an unspecified permission required by the implementation. In the case of the default provider, the SecurityManager.checkRead(String) method is invoked to check read access if the file is opened for reading. The SecurityManager.checkWrite(String) method is invoked to check write access if the file is opened for writing

• size

  public abstract long size()
                     throws IOException

  Returns the current size of this channel's file.

  Returns:

  The current size of this channel's file, measured in bytes

  Throws:

  ClosedChannelException - If this channel is closed

  IOException - If some other I/O error occurs

• truncate

  public abstract AsynchronousFileChannel truncate(long size)
                                            throws IOException

  Truncates this channel's file to the given size.

  If the given size is less than the file's current size then the file is truncated, discarding any bytes beyond the new end of the file. If the given size is greater than or equal to the file's current size then the file is not modified.

  Parameters:

  size - The new size, a non-negative byte count

  Returns:

  This file channel

  Throws:

  NonWritableChannelException - If this channel was not opened for writing

  ClosedChannelException - If this channel is closed

  IllegalArgumentException - If the new size is negative

  IOException - If some other I/O error occurs

• force

  public abstract void force(boolean metaData)
                      throws IOException

  Forces any updates to this channel's file to be written to the storage device that contains it.

  If this channel's file resides on a local storage device then when this method returns it is guaranteed that all changes made to the file since this channel was created, or since this method was last invoked, will have been written to that device. This is useful for ensuring that critical information is not lost in the event of a system crash.

  If the file does not reside on a local device then no such guarantee is made.

  The metaData parameter can be used to limit the number of I/O operations that this method is required to perform. Passing false for this parameter indicates that only updates to the file's content need be written to storage; passing true indicates that updates to both the file's content and metadata must be written, which generally requires at least one more I/O operation. Whether this parameter actually has any effect is dependent upon the underlying operating system and is therefore unspecified.

  Invoking this method may cause an I/O operation to occur even if the channel was only opened for reading. Some operating systems, for example, maintain a last-access time as part of a file's metadata, and this time is updated whenever the file is read. Whether or not this is actually done is system-dependent and is therefore unspecified.

  This method is only guaranteed to force changes that were made to this channel's file via the methods defined in this class.

  Parameters:

  metaData - If true then this method is required to force changes to both the file's content and metadata to be written to storage; otherwise, it need only force content changes to be written

  Throws:

  ClosedChannelException - If this channel is closed

  IOException - If some other I/O error occurs

• lock

  public abstract <A> void lock(long position,
                                long size,
                                boolean shared,
                                A attachment,
                                CompletionHandler<FileLock,? super A> handler)

  Acquires a lock on the given region of this channel's file.

  This method initiates an operation to acquire a lock on the given region of this channel's file. The handler parameter is a completion handler that is invoked when the lock is acquired (or the operation fails). The result passed to the completion handler is the resulting FileLock.

  The region specified by the position and size parameters need not be contained within, or even overlap, the actual underlying file. Lock regions are fixed in size; if a locked region initially contains the end of the file and the file grows beyond the region then the new portion of the file will not be covered by the lock. If a file is expected to grow in size and a lock on the entire file is required then a region starting at zero, and no smaller than the expected maximum size of the file, should be locked. The two-argument lock(Object,CompletionHandler) method simply locks a region of size Long.MAX_VALUE. If a lock that overlaps the requested region is already held by this Java virtual machine, or this method has been invoked to lock an overlapping region and that operation has not completed, then this method throws OverlappingFileLockException.

  Some operating systems do not support a mechanism to acquire a file lock in an asynchronous manner. Consequently an implementation may acquire the file lock in a background thread or from a task executed by a thread in the associated thread pool. If there are many lock operations outstanding then it may consume threads in the Java virtual machine for indefinite periods.

  Some operating systems do not support shared locks, in which case a request for a shared lock is automatically converted into a request for an exclusive lock. Whether the newly-acquired lock is shared or exclusive may be tested by invoking the resulting lock object's isShared method.

  File locks are held on behalf of the entire Java virtual machine. They are not suitable for controlling access to a file by multiple threads within the same virtual machine.

  Type Parameters:

  A - The type of the attachment

  Parameters:

  position - The position at which the locked region is to start; must be non-negative

  size - The size of the locked region; must be non-negative, and the sum position + size must be non-negative

  shared - true to request a shared lock, in which case this channel must be open for reading (and possibly writing); false to request an exclusive lock, in which case this channel must be open for writing (and possibly reading)

  attachment - The object to attach to the I/O operation; can be null

  handler - The handler for consuming the result

  Throws:

  OverlappingFileLockException - If a lock that overlaps the requested region is already held by this Java virtual machine, or there is already a pending attempt to lock an overlapping region

  IllegalArgumentException - If the preconditions on the parameters do not hold

  NonReadableChannelException - If shared is true but this channel was not opened for reading

  NonWritableChannelException - If shared is false but this channel was not opened for writing

• lock

  public final <A> void lock(A attachment,
                             CompletionHandler<FileLock,? super A> handler)

  Acquires an exclusive lock on this channel's file.

  This method initiates an operation to acquire a lock on the given region of this channel's file. The handler parameter is a completion handler that is invoked when the lock is acquired (or the operation fails). The result passed to the completion handler is the resulting FileLock.

  An invocation of this method of the form ch.lock(att,handler) behaves in exactly the same way as the invocation

       ch.lock(0L, Long.MAX_VALUE, false, att, handler)
   

  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:

  OverlappingFileLockException - If a lock is already held by this Java virtual machine, or there is already a pending attempt to lock a region

  NonWritableChannelException - If this channel was not opened for writing

• lock

  public abstract Future<FileLock> lock(long position,
                                        long size,
                                        boolean shared)

  Acquires a lock on the given region of this channel's file.

  This method initiates an operation to acquire a lock on the given region of this channel's file. The method behaves in exactly the same manner as the lock(long, long, boolean, 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 FileLock on successful completion.

  Parameters:

  position - The position at which the locked region is to start; must be non-negative

  size - The size of the locked region; must be non-negative, and the sum position + size must be non-negative

  shared - true to request a shared lock, in which case this channel must be open for reading (and possibly writing); false to request an exclusive lock, in which case this channel must be open for writing (and possibly reading)

  Returns:

  a Future object representing the pending result

  Throws:

  OverlappingFileLockException - If a lock is already held by this Java virtual machine, or there is already a pending attempt to lock a region

  IllegalArgumentException - If the preconditions on the parameters do not hold

  NonReadableChannelException - If shared is true but this channel was not opened for reading

  NonWritableChannelException - If shared is false but this channel was not opened for writing

• lock

  public final Future<FileLock> lock()

  Acquires an exclusive lock on this channel's file.

  This method initiates an operation to acquire an exclusive lock on this channel's file. The method returns a Future representing the pending result of the operation. The Future's get method returns the FileLock on successful completion.

  An invocation of this method behaves in exactly the same way as the invocation

       ch.lock(0L, Long.MAX_VALUE, false)
   

  Returns:

  a Future object representing the pending result

  Throws:

  OverlappingFileLockException - If a lock is already held by this Java virtual machine, or there is already a pending attempt to lock a region

  NonWritableChannelException - If this channel was not opened for writing

• tryLock

  public abstract FileLock tryLock(long position,
                                   long size,
                                   boolean shared)
                            throws IOException

  Attempts to acquire a lock on the given region of this channel's file.

  This method does not block. An invocation always returns immediately, either having acquired a lock on the requested region or having failed to do so. If it fails to acquire a lock because an overlapping lock is held by another program then it returns null. If it fails to acquire a lock for any other reason then an appropriate exception is thrown.

  Parameters:

  position - The position at which the locked region is to start; must be non-negative

  size - The size of the locked region; must be non-negative, and the sum position + size must be non-negative

  shared - true to request a shared lock, false to request an exclusive lock

  Returns:

  A lock object representing the newly-acquired lock, or null if the lock could not be acquired because another program holds an overlapping lock

  Throws:

  IllegalArgumentException - If the preconditions on the parameters do not hold

  ClosedChannelException - If this channel is closed

  OverlappingFileLockException - If a lock that overlaps the requested region is already held by this Java virtual machine, or if another thread is already blocked in this method and is attempting to lock an overlapping region of the same file

  NonReadableChannelException - If shared is true but this channel was not opened for reading

  NonWritableChannelException - If shared is false but this channel was not opened for writing

  IOException - If some other I/O error occurs

  See Also:

  lock(Object,CompletionHandler), lock(long,long,boolean,Object,CompletionHandler), tryLock()

• tryLock

  public final FileLock tryLock()
                         throws IOException

  Attempts to acquire an exclusive lock on this channel's file.

  An invocation of this method of the form ch.tryLock() behaves in exactly the same way as the invocation

       ch.tryLock(0L, Long.MAX_VALUE, false) 

  Returns:

  A lock object representing the newly-acquired lock, or null if the lock could not be acquired because another program holds an overlapping lock

  Throws:

  ClosedChannelException - If this channel is closed

  OverlappingFileLockException - If a lock that overlaps the requested region is already held by this Java virtual machine, or if another thread is already blocked in this method and is attempting to lock an overlapping region

  NonWritableChannelException - If shared is false but this channel was not opened for writing

  IOException - If some other I/O error occurs

  See Also:

  lock(Object,CompletionHandler), lock(long,long,boolean,Object,CompletionHandler), tryLock(long,long,boolean)

• read

  public abstract <A> void read(ByteBuffer dst,
                                long position,
                                A attachment,
                                CompletionHandler<Integer,? super A> handler)

  Reads a sequence of bytes from this channel into the given buffer, starting at the given file position.

  This method initiates the reading of a sequence of bytes from this channel into the given buffer, starting at the given file position. The result of the read is the number of bytes read or -1 if the given position is greater than or equal to the file's size at the time that the read is attempted.

  This method works in the same manner as the AsynchronousByteChannel.read(ByteBuffer,Object,CompletionHandler) method, except that bytes are read starting at the given file position. If the given file position is greater than the file's size at the time that the read is attempted then no bytes are read.

  Type Parameters:

  A - The type of the attachment

  Parameters:

  dst - The buffer into which bytes are to be transferred

  position - The file position at which the transfer is to begin; must be non-negative

  attachment - The object to attach to the I/O operation; can be null

  handler - The handler for consuming the result

  Throws:

  IllegalArgumentException - If the position is negative or the buffer is read-only

  NonReadableChannelException - If this channel was not opened for reading

• read

  public abstract Future<Integer> read(ByteBuffer dst,
                                       long position)

  Reads a sequence of bytes from this channel into the given buffer, starting at the given file position.

  This method initiates the reading of a sequence of bytes from this channel into the given buffer, starting at the given file position. This method returns a Future representing the pending result of the operation. The Future's get method returns the number of bytes read or -1 if the given position is greater than or equal to the file's size at the time that the read is attempted.

  This method works in the same manner as the AsynchronousByteChannel.read(ByteBuffer) method, except that bytes are read starting at the given file position. If the given file position is greater than the file's size at the time that the read is attempted then no bytes are read.

  Parameters:

  dst - The buffer into which bytes are to be transferred

  position - The file position at which the transfer is to begin; must be non-negative

  Returns:

  A Future object representing the pending result

  Throws:

  IllegalArgumentException - If the position is negative or the buffer is read-only

  NonReadableChannelException - If this channel was not opened for reading

• write

  public abstract <A> void write(ByteBuffer src,
                                 long position,
                                 A attachment,
                                 CompletionHandler<Integer,? super A> handler)

  Writes a sequence of bytes to this channel from the given buffer, starting at the given file position.

  This method works in the same manner as the AsynchronousByteChannel.write(ByteBuffer,Object,CompletionHandler) method, except that bytes are written starting at the given file position. If the given position is greater than the file's size, at the time that the write is attempted, then the file will be grown to accommodate the new bytes; the values of any bytes between the previous end-of-file and the newly-written bytes are unspecified.

  Type Parameters:

  A - The type of the attachment

  Parameters:

  src - The buffer from which bytes are to be transferred

  position - The file position at which the transfer is to begin; must be non-negative

  attachment - The object to attach to the I/O operation; can be null

  handler - The handler for consuming the result

  Throws:

  IllegalArgumentException - If the position is negative

  NonWritableChannelException - If this channel was not opened for writing

• write

  public abstract Future<Integer> write(ByteBuffer src,
                                        long position)

  Writes a sequence of bytes to this channel from the given buffer, starting at the given file position.

  This method initiates the writing of a sequence of bytes to this channel from the given buffer, starting at the given file position. The method returns a Future representing the pending result of the write operation. The Future's get method returns the number of bytes written.

  This method works in the same manner as the AsynchronousByteChannel.write(ByteBuffer) method, except that bytes are written starting at the given file position. If the given position is greater than the file's size, at the time that the write is attempted, then the file will be grown to accommodate the new bytes; the values of any bytes between the previous end-of-file and the newly-written bytes are unspecified.

  Parameters:

  src - The buffer from which bytes are to be transferred

  position - The file position at which the transfer is to begin; must be non-negative

  Returns:

  A Future object representing the pending result

  Throws:

  IllegalArgumentException - If the position is negative

  NonWritableChannelException - If this channel was not opened for writing