public Class ReadOnlyFileChannel

Implements abstract java.nio.channels.FileChannel.force.

Doc from java.nio.channels.FileChannel.force.

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, or the methods defined by java.io.FileOutputStream or java.io.RandomAccessFile when the channel was obtained with the getChannel method. 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.

Annotations

@Override

Implements abstract java.nio.channels.FileChannel.lock.

Doc from java.nio.channels.FileChannel.lock.

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 interrupted status will be set and a FileLockInterruptionException will be thrown. If the invoker's interrupted status is set when this method is invoked then that exception will be thrown immediately; the thread's interrupted 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 lock() method simply locks a region of size Long#MAX_VALUE. If the position is non-negative and the size is zero, then a lock of size Long.MAX_VALUE - position is returned.

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.

Annotations

@Override

Implements abstract java.nio.channels.FileChannel.map.

Doc from java.nio.channels.FileChannel.map.

Maps a region of this channel's file directly into memory.

The mode parameter specifies how the region of the file is mapped and may be one of the following modes:

• Read-only: Any attempt to modify the resulting buffer will cause a java.nio.ReadOnlyBufferException to be thrown. (MapMode.READ_ONLY)

• Read/write: Changes made to the resulting buffer will eventually be propagated to the file; they may or may not be made visible to other programs that have mapped the same file. (MapMode.READ_WRITE)

• Private: Changes made to the resulting buffer will not be propagated to the file and will not be visible to other programs that have mapped the same file; instead, they will cause private copies of the modified portions of the buffer to be created. (MapMode.PRIVATE)

An implementation may support additional map modes.

For a read-only mapping, this channel must have been opened for reading; for a read/write or private mapping, this channel must have been opened for both reading and writing.

The mapped byte buffer returned by this method will have a position of zero and a limit and capacity of size; its mark will be undefined. The buffer and the mapping that it represents will remain valid until the buffer itself is garbage-collected.

A mapping, once established, is not dependent upon the file channel that was used to create it. Closing the channel, in particular, has no effect upon the validity of the mapping.

Many of the details of memory-mapped files are inherently dependent upon the underlying operating system and are therefore unspecified. The behavior of this method when the requested region is not completely contained within this channel's file is unspecified. Whether changes made to the content or size of the underlying file, by this program or another, are propagated to the buffer is unspecified. The rate at which changes to the buffer are propagated to the file is unspecified.

For most operating systems, mapping a file into memory is more expensive than reading or writing a few tens of kilobytes of data via the usual read and write methods. From the standpoint of performance it is generally only worth mapping relatively large files into memory.

Annotations

@Override

Implements abstract java.nio.channels.FileChannel.position.

Implements java.nio.channels.SeekableByteChannel.position.

Doc from java.nio.channels.FileChannel.position.

Returns this channel's file position.

Annotations

@Override

Exceptions

IOException:

If some other I/O error occurs

Implements abstract java.nio.channels.FileChannel.position.

Implements java.nio.channels.SeekableByteChannel.position.

Doc from java.nio.channels.FileChannel.position.

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.

Annotations

@Override

Exceptions

IOException:

If some other I/O error occurs

Implements abstract java.nio.channels.FileChannel.read.

Implements java.nio.channels.SeekableByteChannel.read, java.nio.channels.ReadableByteChannel.read.

Doc from java.nio.channels.FileChannel.read.

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.

Annotations

@Override

Exceptions

IOException:

Doc from java.nio.channels.ReadableByteChannel.read.

If some other I/O error occurs

Implements abstract java.nio.channels.FileChannel.read.

Implements java.nio.channels.ScatteringByteChannel.read.

Doc from java.nio.channels.FileChannel.read.

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.

Annotations

@Override

Exceptions

IOException:

Doc from java.nio.channels.ScatteringByteChannel.read.

If some other I/O error occurs

Implements abstract java.nio.channels.FileChannel.read.

Doc from java.nio.channels.FileChannel.read.

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 or equal to the file's current size then no bytes are read.

Annotations

@Override

Exceptions

IOException:

If some other I/O error occurs

Implements abstract java.nio.channels.FileChannel.size.

Implements java.nio.channels.SeekableByteChannel.size.

Doc from java.nio.channels.FileChannel.size.

Returns the current size of this channel's file.

Annotations

@Override

Exceptions

IOException:

If some other I/O error occurs

Implements abstract java.nio.channels.FileChannel.transferFrom.

Doc from java.nio.channels.FileChannel.transferFrom.

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. No bytes are transferred, and zero is returned, if the source has reached end-of-stream.

This method does not modify this channel's position. If the given position is greater than or equal to 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. 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.

Annotations

@Override

Implements abstract java.nio.channels.FileChannel.transferTo.

Doc from java.nio.channels.FileChannel.transferTo.

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 or equal to 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.

Annotations

@Override

Exceptions

IOException:

If some other I/O error occurs

Implements abstract java.nio.channels.FileChannel.truncate.

Implements java.nio.channels.SeekableByteChannel.truncate.

Doc from java.nio.channels.FileChannel.truncate.

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.

Annotations

@Override

Implements abstract java.nio.channels.FileChannel.tryLock.

Doc from java.nio.channels.FileChannel.tryLock.

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 tryLock() method simply locks a region of size Long#MAX_VALUE. If the position is non-negative and the size is zero, then a lock of size Long.MAX_VALUE - position is returned.

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.

Annotations

@Override

Implements abstract java.nio.channels.FileChannel.write.

Doc from java.nio.channels.FileChannel.write.

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 or equal to 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.

If the file is open in append mode, then the effect of invoking this method is unspecified.

Annotations

@Override

Implements abstract java.nio.channels.FileChannel.write.

Implements java.nio.channels.SeekableByteChannel.write, java.nio.channels.WritableByteChannel.write.

Doc from java.nio.channels.FileChannel.write.

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.

Annotations

@Override

Implements abstract java.nio.channels.FileChannel.write.

Implements java.nio.channels.GatheringByteChannel.write.

Doc from java.nio.channels.FileChannel.write.

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.

Annotations

@Override