net.kolotyluk.java.files

Class Files

java.lang.Object

net.kolotyluk.java.files.Files

public class Files
extends Object

Some Useful File System Utilities and Extras

Author:

Eric Kolotyluk

Constructor Summary

Constructors

Constructor and Description
Files()

Method Summary

Methods

Modifier and Type	Method and Description
static void	cleanDirectByteBuffer(ByteBuffer byteBuffer) Clean or unmap a direct ByteBuffer
static Boolean	contentEquals(java.nio.file.Path file1, java.nio.file.Path file2) Identical File Contents

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Files

public Files()

Method Detail

contentEquals

public static Boolean contentEquals(java.nio.file.Path file1,
                    java.nio.file.Path file2)
                             throws IOException

Identical File Contents

Uses Memory Mapped Files for fast comparison of large files. This is about 4 times faster than calling

 org.apache.commons.io.FileUtils.contentEquals(File file1,File file2)

with identical 4 GiB files. Performance may suffer slightly for smaller files. A future version may be optimized for smaller files too.

Useful for checking if media files, such as music and video, have identical or duplicate content. Video files can easily be over 4 GiB in size. Technically this method will compare files as large as the file system supports.

Performance is about 16 seconds for two 4 GiB files with identical content on an Intel Xeon 5580 at 3.2 GHz using a file system on a LSI MegaRAID SAS 9266-8i.

Parameters:

file1 - 1st file to be compared

file2 - 2nd file to be compared

Returns:

true when both files have identical contents

Throws:

IllegalArgumentException - if the arguments are not files.

IOException - if there is a problem with File I/O

RuntimeException - if there was a problem unmapping the buffers or closing the channels, which may leave one or more files locked for read.

cleanDirectByteBuffer

public static void cleanDirectByteBuffer(ByteBuffer byteBuffer)

Clean or unmap a direct ByteBuffer

DirectByteBuffers are garbage collected by using a phantom reference and a reference queue. Every once a while, the JVM checks the reference queue and cleans the DirectByteBuffers. However, as this doesn't happen immediately after discarding all references to a DirectByteBuffer, it's easy get OutOfMemoryError problems using direct ByteBuffers.

Also, if a file is still mapped, via MappedByteBuffer, then it is locked and cannot be destroyed or possibly written to if it was previously mapped read. Trying to destroy or write to a locked file will result in an IOException

This function explicitly calls the cleaner method of a ByteBuffer using reflection because it is not publicly accessible.

Parameters:

byteBuffer - The DirectByteBuffer that will be "cleaned". Returns immediately if the argument is null.

Throws:

IllegalArgumentException - if byteBuffer isn't direct

RuntimeException - if cleaning may have failed