Java in a Nutshell, 5th Edition

Name

MappedByteBuffer

Synopsis

This class is a ByteBuffer that represents a memory-mapped portion of a file. Create a MappedByteBuffer by calling the map( ) method of a java.nio.channels.FileChannel. All MappedByteBuffer buffers are direct buffers.

isLoaded( ) returns a hint as to whether the contents of the buffer are currently in primary memory (as opposed to resident on disk). If it returns true, then operations on the buffer will probably execute very quickly. The load( ) method requests (but does not require) that the operating system load the buffer contents into primary memory. It is not guaranteed to succeed. For buffers that are mapped in read/write mode, the force( ) method outputs any changes that have been made to the buffer contents to the underlying file. If the file is on a local device, then it is guaranteed to be updated before force( ) returns. No such guarantees can be made for mapped network files.

Note that the underlying file of a MappedByteBuffer may be shared, which means that the contents of such a buffer can change asynchronously if the contents of the file are modified by another thread or another process (such asynchronous changes to the underlying file may or may not be visible through the buffer; this is a platform-dependent, and should not be relied on). Furthermore, if another thread or process truncates the file, some or all of the elements of the buffer may no longer map to any content of the file. An attempt to read or write such an inaccesible ...