Java in a Nutshell, 5th Edition

Name

FileChannel

Synopsis

This class implements a communication channel for efficiently reading and and writing files. It implements the standard read( ) and write( ) methods of the ReadableByteChannel, WritableByteChannel, GatheringByteChannel and ScatteringByteChannel methods. In addition, however, FileChannel provides methods for: random-access to the file, efficient transfer of bytes between the file and another channel, file locking, memory mapping, querying and setting the file size and forcing buffered updates to be written to disk. These important features are described in further detail below. Note that since file operations do not typically block for extended periods the way network operations can, FileChannel does not subclass SelectableChannel (it is the only channel class that does not) and cannot be used with Selector objects.

FileChannel has no public constructor and no static factory methods. To obtain a FileChannel, first create a FileInputStream, FileOutputStream, or RandomAccessFile object (see the java.io package) and then call the getChannel( ) method of that object. If you use a FileInputStream, the resulting channel will allow reading but not writing, and if you use a FileOutputStream, the channel will allow writing but not reading. If you obtain a FileChannel from a RandomAccessFile, then the channel will allow reading, or both reading and writing, depending on the mode argument to the RandomAccessFile constructor.

A FileChannel has a position or file pointer ...