Package org.apache.commons.io.input

Class MemoryMappedFileInputStream

java.lang.Object

java.io.InputStream

org.apache.commons.io.input.AbstractInputStream

org.apache.commons.io.input.MemoryMappedFileInputStream

All Implemented Interfaces:

java.io.Closeable, java.lang.AutoCloseable

public final class MemoryMappedFileInputStream
extends AbstractInputStream

An InputStream that utilizes memory mapped files to improve performance. A sliding window of the file is mapped to memory to avoid mapping the entire file to memory at one time. The size of the sliding buffer is configurable.

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

Note: Use of this class does not necessarily obviate the need to use a BufferedInputStream. Depending on the use case, the use of buffering may still further improve performance. For example:

To build an instance, use MemoryMappedFileInputStream.Builder.

 BufferedInputStream s = new BufferedInputStream(new GzipInputStream(
   MemoryMappedFileInputStream.builder()
     .setPath(path)
     .setBufferSize(256 * 1024)
     .get()));
 

should outperform:

 new GzipInputStream(new MemoryMappedFileInputStream(path))
 

 GzipInputStream s = new GzipInputStream(
   MemoryMappedFileInputStream.builder()
     .setPath(path)
     .setBufferSize(256 * 1024)
     .get());
 

Since:

2.12.0

See Also:

MemoryMappedFileInputStream.Builder

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	MemoryMappedFileInputStream.Builder	Builds a new MemoryMappedFileInputStream.

Field Summary

Fields

Modifier and Type	Field	Description
private java.nio.ByteBuffer	buffer
private int	bufferSize
private java.nio.channels.FileChannel	channel
private static int	DEFAULT_BUFFER_SIZE	Default size of the sliding memory mapped buffer.
private static java.nio.ByteBuffer	EMPTY_BUFFER
private long	nextBufferPosition	The starting position (within the file) of the next sliding buffer.

Constructor Summary

Constructors

Modifier	Constructor	Description
private	MemoryMappedFileInputStream(MemoryMappedFileInputStream.Builder builder)	Constructs a new instance.

Method Summary

Modifier and Type	Method	Description
int	available()
static MemoryMappedFileInputStream.Builder	builder()	Constructs a new MemoryMappedFileInputStream.Builder.
private void	cleanBuffer()
void	close()
(package private) int	getBufferSize()
private void	nextBuffer()
int	read()
int	read(byte[] b, int off, int len)
long	skip(long n)

Methods inherited from class org.apache.commons.io.input.AbstractInputStream

checkOpen, isClosed, setClosed

Methods inherited from class java.io.InputStream

mark, markSupported, nullInputStream, read, readAllBytes, readNBytes, readNBytes, reset, transferTo

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_BUFFER_SIZE

private static final int DEFAULT_BUFFER_SIZE

Default size of the sliding memory mapped buffer. We use 256K, equal to 65536 pages (given a 4K page size). Increasing the value beyond the default size will generally not provide any increase in throughput.

See Also:

Constant Field Values

EMPTY_BUFFER

private static final java.nio.ByteBuffer EMPTY_BUFFER

bufferSize

private final int bufferSize

channel

private final java.nio.channels.FileChannel channel

buffer

private java.nio.ByteBuffer buffer

nextBufferPosition

private long nextBufferPosition

The starting position (within the file) of the next sliding buffer.

Constructor Detail

MemoryMappedFileInputStream

private MemoryMappedFileInputStream(MemoryMappedFileInputStream.Builder builder)
                             throws java.io.IOException

Constructs a new instance.

Parameters:

builder - The builder.

Throws:

java.io.IOException - If an I/O error occurs.

Method Detail

builder

public static MemoryMappedFileInputStream.Builder builder()

Constructs a new MemoryMappedFileInputStream.Builder.

Returns:

a new MemoryMappedFileInputStream.Builder.

Since:

2.12.0

available

public int available()
              throws java.io.IOException

Overrides:

available in class java.io.InputStream

Throws:

java.io.IOException

cleanBuffer

private void cleanBuffer()

close

public void close()
           throws java.io.IOException

Specified by:

close in interface java.lang.AutoCloseable

Specified by:

close in interface java.io.Closeable

Overrides:

close in class AbstractInputStream

Throws:

java.io.IOException

getBufferSize

int getBufferSize()

nextBuffer

private void nextBuffer()
                 throws java.io.IOException

Throws:

java.io.IOException

read

public int read()
         throws java.io.IOException

Specified by:

read in class java.io.InputStream

Throws:

java.io.IOException

read

public int read(byte[] b,
                int off,
                int len)
         throws java.io.IOException

Overrides:

read in class java.io.InputStream

Throws:

java.io.IOException

skip

public long skip(long n)
          throws java.io.IOException

Overrides:

skip in class java.io.InputStream

Throws:

java.io.IOException