java.lang.Object | |||
java.nio.channels.spi.AbstractInterruptibleChannel | Channel InterruptibleChannel | ||
java.nio.channels.FileChannel | ByteChannel GatheringByteChannel ScatteringByteChannel |
An abstract channel type for interaction with a platform file.
A FileChannel defines the methods for reading, writing, memory mapping, and
manipulating the logical state of a platform file. This type does not have a
method for opening files, since this behaviour has been delegated to the
FileInputStream
, FileOutputStream
, and
RandomAccessFile
types.
FileChannels created from a FileInputStream, or a RandomAccessFile created in mode "r", are read-only. FileChannels created from a FileOutputStream are write-only. FileChannels created from a RandomAccessFile created in mode "rw" are read/write. FileChannels created from a RandomAccessFile that was opened in append-mode will also be in append-mode -- meaning that each write will be proceeded by a seek to the end of file. Some platforms will seek and write atomically, others will not.
FileChannels has a virtual pointer into the file which is referred to as a file position. The position can be manipulated by repositioning it within the file, and its current position can be queried.
FileChannels also have an associated size. The size of the file is the number of bytes that it currently contains. The size can be manipulated by adding more bytes to the end of the file (which increases the size) or truncating the file (which decreases the size). The current size can also be queried.
FileChannels have operations beyond the simple read, write, and close. They can also:
FileChannels are thread-safe. Only one operation involving manipulation of the file position may be in-flight at once. Subsequent calls to such operations will block, and one of those blocked will be freed to continue when the first operation has completed. There is no ordered queue or fairness applied to the blocked threads.
It is undefined whether operations that do not manipulate the file position will also block when there are any other operations in-flight.
The logical view of the underlying file is consistent across all FileChannels and IO streams opened on the same file by the same JVM process. Therefore modifications performed via a channel will be visible to the stream, and vice versa; including modifications to the file position, content, size, etc.
FileChannel.MapMode | A type of file mapping modes. |
FileChannel() | ||||||
Protected default constructor. |
abstract | void | force(boolean metadata) | ||||
Request that all updates to the channel are committed to the storage device. | ||||||
abstract | FileLock | lock(long position, long size, boolean shared) | ||||
Obtain a lock on a specified region of the file. | ||||||
final | FileLock | lock() | ||||
Obtain an exclusive lock on this file. | ||||||
abstract | MappedByteBuffer | map(FileChannel.MapMode mode, long position, long size) | ||||
Maps the file into memory.There can be three modes:Read-only,Read/write and Private. | ||||||
abstract | long | position() | ||||
Returns the current value of the file position pointer. | ||||||
abstract | FileChannel | position(long offset) | ||||
Sets the file position pointer to a new value. | ||||||
abstract | long | read(ByteBuffer[] buffers, int start, int number) | ||||
Reads bytes from the file channel into a subset of the given byte buffers. | ||||||
abstract | int | read(ByteBuffer buffer) | ||||
Reads bytes from the channel into the given byte buffer. | ||||||
abstract | int | read(ByteBuffer buffer, long position) | ||||
Reads bytes from the file channel into the given buffer starting from the given file position. | ||||||
final | long | read(ByteBuffer[] buffers) | ||||
Reads bytes from the channel into all the given byte buffers. | ||||||
abstract | long | size() | ||||
Returns the size of the file underlying this channel, in bytes. | ||||||
abstract | long | transferFrom(ReadableByteChannel src, long position, long count) | ||||
Transfers bytes into this channel's file from the given readable byte channel. | ||||||
abstract | long | transferTo(long position, long count, WritableByteChannel target) | ||||
Transfers data from the file to the given channel. | ||||||
abstract | FileChannel | truncate(long size) | ||||
Truncates the file underlying this channel to a given size. | ||||||
final | FileLock | tryLock() | ||||
Attempts to acquire an exclusive lock on this file without blocking. | ||||||
abstract | FileLock | tryLock(long position, long size, boolean shared) | ||||
Attempts to acquire an exclusive lock on this file without blocking. | ||||||
abstract | long | write(ByteBuffer[] buffers, int offset, int length) | ||||
Writes a subset of the given bytes from the buffers to the channel. | ||||||
abstract | int | write(ByteBuffer buffer, long position) | ||||
Writes bytes from the given buffer to the file channel starting at the given file position. | ||||||
final | long | write(ByteBuffer[] buffers) | ||||
Writes bytes from all the given byte buffers into the file channel. | ||||||
abstract | int | write(ByteBuffer src) | ||||
Writes bytes from the given byte buffer into the file channel. |
When this method returns all modifications made to the platform file underlying this channel will be committed to a local storage device. If the file is not hosted locally, such as a networked file system, then applications cannot be certain that the modifications have been committed.
There are no assurances given that changes made to the file using methods defined elsewhere will be committed. For example, changes made via a mapped byte buffer may not be committed.
The metadata
parameter indicated whether the update should
include the file's metadata such as last modification time, last access
time, etc. Note that passing true
may invoke an underlying
write to the operating system (if the platform is maintaining metadata
such as last access time), even if the channel is opened read-only.
metadata | true if the file metadata should be flushed in addition to the file content, and false otherwise. |
---|
ClosedChannelException | if the channel is already closed. |
---|---|
IOException | some other problem occurred. |
This is the blocking version of lock acquisition, see also the
tryLock()
methods.
Attempts to acquire an overlapping lock region will fail. The attempt will fail if the overlapping lock has already been obtained, or if another thread is currently waiting to acquire the overlapping lock.
If the request is not for an overlapping lock, the thread calling this method will block until the lock is obtained (likely by no contention or another process releasing a lock), or this thread being interrupted or the channel closed.
If the lock is obtained successfully then the FileLock object returned represents the lock for subsequent operations on the locked region.
If the thread is interrupted while waiting for the lock, the thread is
set to the interrupted state, and throws a
FileLockInterruptionException
. If the channel is closed
while the thread is waiting to obtain the lock then the thread throws a
AsynchronousCloseException
.
There is no requirement for the position and size to be within the current start and length of the file.
Some platforms do not support shared locks, and if a request is made for a shared lock on such a platform this method will attempt to acquire an exclusive lock instead. It is undefined whether the lock obtained is advisory or mandatory.
position | the starting position for the lock region |
---|---|
size | the length of the lock, in bytes |
shared | a flag indicating whether an attempt should be made to acquire a shared lock. |
IllegalArgumentException | if the parameters are invalid. |
---|---|
ClosedChannelException | if the channel is already closed. |
OverlappingFileLockException | if the requested region overlaps an existing lock or pending lock request. |
NonReadableChannelException | if the channel is not open in read-mode and shared is true. |
NonWritableChannelException | if the channel is not open in write mode and shared is false. |
AsynchronousCloseException | if the channel is closed by another thread while this method is in operation. |
FileLockInterruptionException | if the thread is interrupted while in the state of waiting on the desired file lock. |
IOException | if some other IO problem occurs. |
This is a convenience method for acquiring a maximum length lock on a file. It is equivalent to:
fileChannel.lock(0L, Long.MAX_VALUE, false)
ClosedChannelException | the file channel is closed. |
---|---|
NonWritableChannelException | this channel was not opened for writing. |
OverlappingFileLockException | Either a lock is already held that overlaps this lock request, or another thread is waiting to acquire a lock that will overlap with this request. |
FileLockInterruptionException | The calling thread was interrupted while waiting to acquire the lock. |
AsynchronousCloseException | The channel was closed while the calling thread was waiting to acquire the lock. |
IOException | some other problem occurred obtaining the requested lock. |
mode | one of three modes to map |
---|---|
position | the starting position of the file |
size | the size to map |
NonReadableChannelException | If the file is not opened for reading but the given mode is "READ_ONLY" |
---|---|
NonWritableChannelException | If the file is not opened for writing but the mode is not "READ_ONLY" |
IllegalArgumentException | If the given parameters of position and size are not correct |
IOException | If any I/O error occurs |
ClosedChannelException | if the channel is already closed. |
---|---|
IOException | if some other IO problem occurs. |
The argument is the number of bytes counted from the start of the file. The position cannot be set to a value that is negative. The new position can be set beyond the current file size. If set beyond the current file size, attempts to read will return end of file, and writes will succeed, but fill-in the bytes between the current end of file and the position with the required number of (unspecified) byte values.
offset | the new file position, in bytes. |
---|
IllegalArgumentException | if the new position is negative. |
---|---|
ClosedChannelException | if the channel is already closed. |
IOException | if some other IO problem occurs. |
IOException |
---|
The bytes are read starting at the current file position, and after some number of bytes are read (up to the remaining number of bytes in the buffer) the file position is increased by the number of bytes actually read.
IOException |
---|
The bytes are read starting at the given file position (up to the remaining number of bytes in the buffer). The number of bytes actually read is returned.
If the position is beyond the current end of file, then no bytes are read.
Note that file position is unmodified by this method.
buffer | the buffer to receive the bytes |
---|---|
position | the (non-negative) position at which to read the bytes. |
IllegalArgumentException | if position is less than -1 . |
---|---|
ClosedChannelException | if the channel is already closed. |
NonReadableChannelException | if the channel was not opened in read-mode. |
AsynchronousCloseException | if the channel is closed by another thread while this method is in operation. |
ClosedByInterruptException | if another thread interrupts the calling thread while the operation is in progress. The calling thread will have the interrupt state set, and the channel will be closed. |
IOException | some other IO error occurred. |
The bytes are read starting at the current file position, and after some number of bytes are read (up to the remaining number of bytes in all the buffers) the file position is increased by the number of bytes actually read.
This method behaves exactly like:
read(buffers, 0, buffers.length);
IOException |
---|
ClosedChannelException | if the channel is closed. |
---|---|
IOException | if a problem occurs getting the size of the file. |
src | the source channel to read |
---|---|
position | the non-negative position to begin |
count | the non-negative bytes to be transferred |
IllegalArgumentException | If the parameters are not correct |
---|---|
NonReadableChannelException | If the source channel is not readable |
NonWritableChannelException | If this channel is not writable |
ClosedChannelException | If either channel has already been closed |
AsynchronousCloseException | If either channel is closed by other threads during this operation |
ClosedByInterruptException | If the thread is interrupted during this operation |
IOException | If any I/O error occurs |
position | the non-negative position to begin |
---|---|
count | the non-negative bytes to be transferred |
target | the target channel to write into |
IllegalArgumentException | If the parameters are not correct |
---|---|
NonReadableChannelException | If this channel is not readable |
NonWritableChannelException | If the target channel is not writable |
ClosedChannelException | If either channel has already been closed |
AsynchronousCloseException | If either channel is closed by other threads during this operation |
ClosedByInterruptException | If the thread is interrupted during this operation |
IOException | If any I/O error occurs |
Any bytes beyond the given size are removed from the file. If there are no bytes beyond the given size then the file contents are unmodified.
If the file position is currently greater than the given size, then it is set to be the given size.
size | the maximum size of the underlying file |
---|
IllegalArgumentException | the requested size is negative. |
---|---|
ClosedChannelException | the channel is closed. |
NonWritableChannelException | the channel cannot be written. |
IOException | some other IO problem occurred. |
This is a convenience method for attempting to acquire a maximum length lock on the file. It is equivalent to:
fileChannel.tryLock(0L, Long.MAX_VALUE, false)
The method returns null
if the acquisition would result in
an overlapped lock with another OS process.
null
if the lock would
overlap an existing exclusive lock in another OS process.ClosedChannelException | the file channel is closed. |
---|---|
OverlappingFileLockException | Either a lock is already held that overlaps this lock request, or another thread is waiting to acquire a lock that will overlap with this request. |
IOException | if any I/O error occurs |
The method returns null
if the acquisition would result in
an overlapped lock with another OS process.
position | the starting position |
---|---|
size | the size of file to lock |
shared | true if share |
null
if the lock would
overlap an existing exclusive lock in another OS process.IllegalArgumentException | If any parameters are bad |
---|---|
ClosedChannelException | the file channel is closed. |
OverlappingFileLockException | Either a lock is already held that overlaps this lock request, or another thread is waiting to acquire a lock that will overlap with this request. |
IOException | if any I/O error occurs |
This method attempts to write all of the remaining()
bytes
from length
byte buffers, in order, starting at
buffers[offset]
. The number of bytes actually written is
returned.
If a write operation is in progress, subsequent threads will block until the write is completed, and will then contend for the ability to write.
IOException |
---|
The bytes are written starting at the given file position (up to the remaining number of bytes in the buffer). The number of bytes actually written is returned.
If the position is beyond the current end of file, then the file is first extended up to the given position by the required number of unspecified byte values.
Note that file position is unmodified by this method.
buffer | the buffer containing the bytes to be written. |
---|---|
position | the (non-negative) position at which to write the bytes. |
IllegalArgumentException | if position is less than -1 . |
---|---|
ClosedChannelException | if the channel is already closed. |
NonWritableChannelException | if the channel was not opened in write-mode. |
AsynchronousCloseException | if the channel is closed by another thread while this method is in operation. |
ClosedByInterruptException | if another thread interrupts the calling thread while the operation is in progress. The calling thread will have the interrupt state set, and the channel will be closed. |
IOException | some other IO error occurred. |
The bytes are written starting at the current file position, and after some number of bytes are written (up to the remaining number of bytes in all the buffers) the file position is increased by the number of bytes actually written.
This method behaves exactly like:
write(buffers, 0, buffers.length);
IOException |
---|
The bytes are written starting at the current file position, and after some number of bytes are written (up to the remaining number of bytes in the buffer) the file position is increased by the number of bytes actually written.
src | the source buffer to write |
---|
IOException |
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Copyright 2007 Google Inc. | Build 0.9_r1-98467 - 14 Aug 2008 18:56 |