Package software.amazon.nio.spi.s3

Class S3FileChannel

java.lang.Object

java.nio.channels.spi.AbstractInterruptibleChannel

java.nio.channels.FileChannel

software.amazon.nio.spi.s3.S3FileChannel

All Implemented Interfaces:

java.io.Closeable, java.lang.AutoCloseable, java.nio.channels.ByteChannel, java.nio.channels.Channel, java.nio.channels.GatheringByteChannel, java.nio.channels.InterruptibleChannel, java.nio.channels.ReadableByteChannel, java.nio.channels.ScatteringByteChannel, java.nio.channels.SeekableByteChannel, java.nio.channels.WritableByteChannel

public class S3FileChannel
extends java.nio.channels.FileChannel

Nested Class Summary

Nested classes/interfaces inherited from class java.nio.channels.FileChannel

java.nio.channels.FileChannel.MapMode

Method Summary

Modifier and Type	Method	Description
void	force(boolean metaData)	Forces any updates to this channel's file to be written to the storage device that contains it.
protected void	implCloseChannel()	Closes this channel.
java.nio.channels.FileLock	lock(long position, long size, boolean shared)	Acquires a lock on the given region of this channel's file.
java.nio.MappedByteBuffer	map(java.nio.channels.FileChannel.MapMode mode, long position, long size)	This method is not supported by this implementation, and the IOException thrown always includes the message "This library current doesn't support MappedByteBuffers".
long	position()	Returns this channel's file position.
java.nio.channels.FileChannel	position(long newPosition)	Sets this channel's file position.
int	read(java.nio.ByteBuffer dst)	Reads a sequence of bytes from this channel into the given buffer.
long	read(java.nio.ByteBuffer[] dsts, int offset, int length)	Reads a sequence of bytes from this channel into a subsequence of the given buffers.
int	read(java.nio.ByteBuffer dst, long position)	Reads a sequence of bytes from this channel into the given buffer, starting at the given file position.
long	size()	Returns the current size of this channel's file.
long	transferFrom(java.nio.channels.ReadableByteChannel src, long position, long count)	Transfers bytes into this channel's file from the given readable byte channel.
long	transferTo(long position, long count, java.nio.channels.WritableByteChannel target)	Transfers bytes from this channel's file to the given writable byte channel.
java.nio.channels.FileChannel	truncate(long size)	Truncates this channel's file to the given size.
java.nio.channels.FileLock	tryLock(long position, long size, boolean shared)	Attempts to acquire a lock on the given region of this channel's file.
int	write(java.nio.ByteBuffer src)	Writes a sequence of bytes to this channel from the given buffer.
long	write(java.nio.ByteBuffer[] srcs, int offset, int length)	Writes a sequence of bytes to this channel from a subsequence of the given buffers.
int	write(java.nio.ByteBuffer src, long position)	Writes a sequence of bytes to this channel from the given buffer, starting at the given file position.

Methods inherited from class java.nio.channels.FileChannel

lock, open, open, read, tryLock, write

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

isOpen

Method Detail

read

public int read(java.nio.ByteBuffer dst)
         throws java.io.IOException

Reads a sequence of bytes from this channel into the given buffer.

Bytes are read starting at this channel's current file position, and then the file position is updated with the number of bytes actually read. Otherwise this method behaves exactly as specified in the ReadableByteChannel interface.

Specified by:

read in interface java.nio.channels.ReadableByteChannel

Specified by:

read in interface java.nio.channels.SeekableByteChannel

Specified by:

read in class java.nio.channels.FileChannel

Parameters:

dst - the destination to read bytes into.

Throws:

java.io.IOException

read

public long read(java.nio.ByteBuffer[] dsts,
                 int offset,
                 int length)
          throws java.io.IOException

Reads a sequence of bytes from this channel into a subsequence of the given buffers.

Bytes are read starting at this channel's current file position, and then the file position is updated with the number of bytes actually read. Otherwise this method behaves exactly as specified in the ScatteringByteChannel interface.

Specified by:

read in interface java.nio.channels.ScatteringByteChannel

Specified by:

read in class java.nio.channels.FileChannel

Parameters:

dsts - the buffer array

offset - the index of the destination buffer in the buffer array to start reading into

length - the number of buffers in the array to read bytes into

Returns:

the number of bytes read into the buffer

Throws:

java.io.IOException

write

public int write(java.nio.ByteBuffer src)
          throws java.io.IOException

Writes a sequence of bytes to this channel from the given buffer.

Bytes are written starting at this channel's current file position unless the channel is in append mode, in which case the position is first advanced to the end of the file. The file is grown, if necessary, to accommodate the written bytes, and then the file position is updated with the number of bytes actually written. Otherwise this method behaves exactly as specified by the WritableByteChannel interface.

Specified by:

write in interface java.nio.channels.SeekableByteChannel

Specified by:

write in interface java.nio.channels.WritableByteChannel

Specified by:

write in class java.nio.channels.FileChannel

Parameters:

src - the source of the bytes to write into this channel

Returns:

the number of bytes actually written

Throws:

java.io.IOException

write

public long write(java.nio.ByteBuffer[] srcs,
                  int offset,
                  int length)
           throws java.io.IOException

Writes a sequence of bytes to this channel from a subsequence of the given buffers.

Bytes are written starting at this channel's current file position unless the channel is in append mode, in which case the position is first advanced to the end of the file. The file is grown, if necessary, to accommodate the written bytes, and then the file position is updated with the number of bytes actually written. Otherwise this method behaves exactly as specified in the GatheringByteChannel interface.

Specified by:

write in interface java.nio.channels.GatheringByteChannel

Specified by:

write in class java.nio.channels.FileChannel

Parameters:

srcs - the source of the bytes to write into this channel

offset - the index of the first buffer in the buffer array to write bytes from

length - the maximum number of buffers to write bytes from

Returns:

the number of bytes actually written

Throws:

java.io.IOException

position

public long position()
              throws java.io.IOException

Returns this channel's file position.

Specified by:

position in interface java.nio.channels.SeekableByteChannel

Specified by:

position in class java.nio.channels.FileChannel

Returns:

This channel's file position, a non-negative integer counting the number of bytes from the beginning of the file to the current position

Throws:

java.nio.channels.ClosedChannelException - If this channel is closed

java.io.IOException - If some other I/O error occurs

position

public java.nio.channels.FileChannel position(long newPosition)
                                       throws java.io.IOException

Sets this channel's file position.

Setting the position to a value that is greater than the file's current size is legal but does not change the size of the file. A later attempt to read bytes at such a position will immediately return an end-of-file indication. A later attempt to write bytes at such a position will cause the file to 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.

Specified by:

position in interface java.nio.channels.SeekableByteChannel

Specified by:

position in class java.nio.channels.FileChannel

Parameters:

newPosition - The new position, a non-negative integer counting the number of bytes from the beginning of the file

Returns:

This file channel

Throws:

java.nio.channels.ClosedChannelException - If this channel is closed

java.lang.IllegalArgumentException - If the new position is negative

java.io.IOException - If some other I/O error occurs

size

public long size()
          throws java.io.IOException

Returns the current size of this channel's file.

Specified by:

size in interface java.nio.channels.SeekableByteChannel

Specified by:

size in class java.nio.channels.FileChannel

Returns:

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

Throws:

java.nio.channels.ClosedChannelException - If this channel is closed

java.io.IOException - If some other I/O error occurs

truncate

public java.nio.channels.FileChannel truncate(long size)
                                       throws java.io.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. In either case, if this channel's file position is greater than the given size then it is set to that size.

Specified by:

truncate in interface java.nio.channels.SeekableByteChannel

Specified by:

truncate in class java.nio.channels.FileChannel

Parameters:

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

Returns:

This file channel

Throws:

java.nio.channels.NonWritableChannelException - If this channel was not opened for writing

java.nio.channels.ClosedChannelException - If this channel is closed

java.lang.IllegalArgumentException - If the new size is negative

java.io.IOException - If some other I/O error occurs

force

public void force(boolean metaData)
           throws java.io.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. It may or may not force changes that were made by modifying the content of a mapped byte buffer obtained by invoking the map method. Invoking the force method of the mapped byte buffer will force changes made to the buffer's content to be written.

Specified by:

force in class java.nio.channels.FileChannel

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:

java.nio.channels.ClosedChannelException - If this channel is closed

java.io.IOException - If some other I/O error occurs

transferTo

public long transferTo(long position,
                       long count,
                       java.nio.channels.WritableByteChannel target)
                throws java.io.IOException

Transfers bytes from this channel's file to the given writable byte channel.

An attempt is made to read up to count bytes starting at the given position in this channel's file and write them to the target channel. An invocation of this method may or may not transfer all of the requested bytes; whether or not it does so depends upon the natures and states of the channels. Fewer than the requested number of bytes are transferred if this channel's file contains fewer than count bytes starting at the given position, or if the target channel is non-blocking and it has fewer than count bytes free in its output buffer.

This method does not modify this channel's position. If the given position is greater than the file's current size then no bytes are transferred. If the target channel has a position then bytes are written starting at that position and then the position is incremented by the number of bytes written.

This method is potentially much more efficient than a simple loop that reads from this channel and writes to the target channel. Many operating systems can transfer bytes directly from the filesystem cache to the target channel without actually copying them.

Specified by:

transferTo in class java.nio.channels.FileChannel

Parameters:

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

count - The maximum number of bytes to be transferred; must be non-negative

target - The target channel

Returns:

The number of bytes, possibly zero, that were actually transferred

Throws:

java.lang.IllegalArgumentException - If the preconditions on the parameters do not hold

java.nio.channels.NonReadableChannelException - If this channel was not opened for reading

java.nio.channels.NonWritableChannelException - If the target channel was not opened for writing

java.nio.channels.ClosedChannelException - If either this channel or the target channel is closed

java.nio.channels.AsynchronousCloseException - If another thread closes either channel while the transfer is in progress

java.nio.channels.ClosedByInterruptException - If another thread interrupts the current thread while the transfer is in progress, thereby closing both channels and setting the current thread's interrupt status

java.io.IOException - If some other I/O error occurs

transferFrom

public long transferFrom(java.nio.channels.ReadableByteChannel src,
                         long position,
                         long count)
                  throws java.io.IOException

Transfers bytes into this channel's file from the given readable byte channel.

An attempt is made to read up to count bytes from the source channel and write them to this channel's file starting at the given position. An invocation of this method may or may not transfer all of the requested bytes; whether or not it does so depends upon the natures and states of the channels. Fewer than the requested number of bytes will be transferred if the source channel has fewer than count bytes remaining, or if the source channel is non-blocking and has fewer than count bytes immediately available in its input buffer.

This method does not modify this channel's position. If the given position is greater than the file's current size then no bytes are transferred. If the source channel has a position then bytes are read starting at that position and then the position is incremented by the number of bytes read.

This method is potentially much more efficient than a simple loop that reads from the source channel and writes to this channel. Many operating systems can transfer bytes directly from the source channel into the filesystem cache without actually copying them.

Specified by:

transferFrom in class java.nio.channels.FileChannel

Parameters:

src - The source channel

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

count - The maximum number of bytes to be transferred; must be non-negative

Returns:

The number of bytes, possibly zero, that were actually transferred

Throws:

java.lang.IllegalArgumentException - If the preconditions on the parameters do not hold

java.nio.channels.NonReadableChannelException - If the source channel was not opened for reading

java.nio.channels.NonWritableChannelException - If this channel was not opened for writing

java.nio.channels.ClosedChannelException - If either this channel or the source channel is closed

java.nio.channels.AsynchronousCloseException - If another thread closes either channel while the transfer is in progress

java.nio.channels.ClosedByInterruptException - If another thread interrupts the current thread while the transfer is in progress, thereby closing both channels and setting the current thread's interrupt status

java.io.IOException - If some other I/O error occurs

read

public int read(java.nio.ByteBuffer dst,
                long position)
         throws java.io.IOException

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

This method works in the same manner as the read(ByteBuffer) method, except that bytes are read starting at the given file position rather than at the channel's current position. This method does not modify this channel's position. If the given position is greater than the file's current size then no bytes are read.

Specified by:

read in class java.nio.channels.FileChannel

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:

The number of bytes read, possibly zero, or -1 if the given position is greater than or equal to the file's current size

Throws:

java.lang.IllegalArgumentException - If the position is negative

java.nio.channels.NonReadableChannelException - If this channel was not opened for reading

java.nio.channels.ClosedChannelException - If this channel is closed

java.nio.channels.AsynchronousCloseException - If another thread closes this channel while the read operation is in progress

java.nio.channels.ClosedByInterruptException - If another thread interrupts the current thread while the read operation is in progress, thereby closing the channel and setting the current thread's interrupt status

java.io.IOException - If some other I/O error occurs

write

public int write(java.nio.ByteBuffer src,
                 long position)
          throws java.io.IOException

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 write(ByteBuffer) method, except that bytes are written starting at the given file position rather than at the channel's current position. This method does not modify this channel's position. If the given position is greater than the file's current size 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.

Specified by:

write in class java.nio.channels.FileChannel

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:

The number of bytes written, possibly zero

Throws:

java.lang.IllegalArgumentException - If the position is negative

java.nio.channels.NonWritableChannelException - If this channel was not opened for writing

java.nio.channels.ClosedChannelException - If this channel is closed

java.nio.channels.AsynchronousCloseException - If another thread closes this channel while the write operation is in progress

java.nio.channels.ClosedByInterruptException - If another thread interrupts the current thread while the write operation is in progress, thereby closing the channel and setting the current thread's interrupt status

java.io.IOException - If some other I/O error occurs

map

public java.nio.MappedByteBuffer map(java.nio.channels.FileChannel.MapMode mode,
                                     long position,
                                     long size)
                              throws java.io.IOException

This method is not supported by this implementation, and the IOException thrown always includes the message "This library current doesn't support MappedByteBuffers".

Specified by:

map in class java.nio.channels.FileChannel

Parameters:

mode - One of the constants READ_ONLY, READ_WRITE, or PRIVATE defined in the FileChannel.MapMode class, according to whether the file is to be mapped read-only, read/write, or privately (copy-on-write), respectively

position - The position within the file at which the mapped region is to start; must be non-negative

size - The size of the region to be mapped; must be non-negative and no greater than Integer.MAX_VALUE

Returns:

Never returns, always throws an exception

Throws:

java.io.IOException - Always throws an exception

lock

public java.nio.channels.FileLock lock(long position,
                                       long size,
                                       boolean shared)
                                throws java.io.IOException

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

An invocation of this method will block until the region can be locked, this channel is closed, or the invoking thread is interrupted, whichever comes first.

If this channel is closed by another thread during an invocation of this method then an AsynchronousCloseException will be thrown.

If the invoking thread is interrupted while waiting to acquire the lock then its interrupt status will be set and a FileLockInterruptionException will be thrown. If the invoker's interrupt status is set when this method is invoked then that exception will be thrown immediately; the thread's interrupt status will not be changed.

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 zero-argument FileChannel.lock() method simply locks a region of size Long.MAX_VALUE.

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.

Specified by:

lock in class java.nio.channels.FileChannel

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 lock object representing the newly-acquired lock

Throws:

java.lang.IllegalArgumentException - If the preconditions on the parameters do not hold

java.nio.channels.ClosedChannelException - If this channel is closed

java.nio.channels.AsynchronousCloseException - If another thread closes this channel while the invoking thread is blocked in this method

java.nio.channels.FileLockInterruptionException - If the invoking thread is interrupted while blocked in this method

java.nio.channels.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

java.nio.channels.NonReadableChannelException - If shared is true this channel was not opened for reading

java.nio.channels.NonWritableChannelException - If shared is false but this channel was not opened for writing

java.io.IOException - If some other I/O error occurs

See Also:

FileChannel.lock(), FileChannel.tryLock(), tryLock(long, long, boolean)

tryLock

public java.nio.channels.FileLock tryLock(long position,
                                          long size,
                                          boolean shared)
                                   throws java.io.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.

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 zero-argument FileChannel.tryLock() method simply locks a region of size Long.MAX_VALUE.

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.

Specified by:

tryLock in class java.nio.channels.FileChannel

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:

java.lang.IllegalArgumentException - If the preconditions on the parameters do not hold

java.nio.channels.ClosedChannelException - If this channel is closed

java.nio.channels.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

java.io.IOException - If some other I/O error occurs

See Also:

FileChannel.lock(), lock(long, long, boolean), FileChannel.tryLock()

implCloseChannel

protected void implCloseChannel()
                         throws java.io.IOException

Closes this channel.

This method is invoked by the close method in order to perform the actual work of closing the channel. This method is only invoked if the channel has not yet been closed, and it is never invoked more than once.

An implementation of this method must arrange for any other thread that is blocked in an I/O operation upon this channel to return immediately, either by throwing an exception or by returning normally.

Specified by:

implCloseChannel in class java.nio.channels.spi.AbstractInterruptibleChannel

Throws:

java.io.IOException - If an I/O error occurs while closing the channel