com.drew.imaging.jpeg
Class JpegSegmentReader

java.lang.Object
  com.drew.imaging.jpeg.JpegSegmentReader

public class JpegSegmentReader
extends Object

Performs read functions of Jpeg files, returning specific file segments. TODO add a findAvailableSegments() method TODO add more segment identifiers TODO add a getSegmentDescription() method, returning for example 'App1 application data segment, commonly containing Exif data'

Author:

Drew Noakes http://drewnoakes.com

Field Summary

private byte[]	_data Jpeg data as byte array
private File	_file Jpeg file
private JpegSegmentData	_segmentData
private InputStream	_stream Jpeg data as an InputStream
private static byte	MARKER_EOI Private, because one wouldn't search for it.
static byte	SEGMENT_APP0 APP0 Jpeg segment identifier -- Jfif data.
static byte	SEGMENT_APP1 APP1 Jpeg segment identifier -- where Exif data is kept.
static byte	SEGMENT_APP2 APP2 Jpeg segment identifier.
static byte	SEGMENT_APP3 APP3 Jpeg segment identifier.
static byte	SEGMENT_APP4 APP4 Jpeg segment identifier.
static byte	SEGMENT_APP5 APP5 Jpeg segment identifier.
static byte	SEGMENT_APP6 APP6 Jpeg segment identifier.
static byte	SEGMENT_APP7 APP7 Jpeg segment identifier.
static byte	SEGMENT_APP8 APP8 Jpeg segment identifier.
static byte	SEGMENT_APP9 APP9 Jpeg segment identifier.
static byte	SEGMENT_APPA APPA Jpeg segment identifier -- can hold Unicode comments.
static byte	SEGMENT_APPB APPB Jpeg segment identifier.
static byte	SEGMENT_APPC APPC Jpeg segment identifier.
static byte	SEGMENT_APPD APPD Jpeg segment identifier -- IPTC data in here.
static byte	SEGMENT_APPE APPE Jpeg segment identifier.
static byte	SEGMENT_APPF APPF Jpeg segment identifier.
static byte	SEGMENT_COM Jpeg comment segment identifier.
static byte	SEGMENT_DHT Define Huffman Table segment identifier.
static byte	SEGMENT_DQT Define Quantization Table segment identifier.
static byte	SEGMENT_SOF0 Start-of-Frame Zero segment identifier.
static byte	SEGMENT_SOI Start Of Image segment identifier.
private static byte	SEGMENT_SOS Private, because this segment crashes my algorithm, and searching for it doesn't work (yet).

Constructor Summary

JpegSegmentReader(byte[] fileContents)
Creates a JpegSegmentReader for a byte array.

JpegSegmentReader(File file)
Creates a JpegSegmentReader for a specific file.

JpegSegmentReader(InputStream in)
Creates a JpegSegmentReader for an InputStream.

JpegSegmentReader(JpegSegmentData segmentData)
Creates a JpegSegmentReader for a JpegSegmentData.

Method Summary

private BufferedInputStream	getJpegInputStream() Private helper method to create a BufferedInputStream of Jpeg data from whichever data source was specified upon construction of this instance.
int	getSegmentCount(byte segmentMarker) Returns the number of segments having the specified JPEG segment marker.
JpegSegmentData	getSegmentData() Returns the JpegSegmentData object used by this reader.
private boolean	isValidJpegHeaderBytes(InputStream fileStream) Helper method that validates the Jpeg file's magic number.
byte[]	readSegment(byte segmentMarker) Reads the first instance of a given Jpeg segment, returning the contents as a byte array.
byte[]	readSegment(byte segmentMarker, int occurrence) Reads the first instance of a given Jpeg segment, returning the contents as a byte array.
private void	readSegments()

Methods inherited from class java.lang.Object

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

Field Detail

_file

private final File _file

Jpeg file

_data

private final byte[] _data

Jpeg data as byte array

_stream

private final InputStream _stream

Jpeg data as an InputStream

_segmentData

private JpegSegmentData _segmentData

SEGMENT_SOS

private static final byte SEGMENT_SOS

Private, because this segment crashes my algorithm, and searching for it doesn't work (yet).

See Also:

Constant Field Values

MARKER_EOI

private static final byte MARKER_EOI

Private, because one wouldn't search for it.

See Also:

Constant Field Values

SEGMENT_APP0

public static final byte SEGMENT_APP0

APP0 Jpeg segment identifier -- Jfif data.

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Constant Field Values

SEGMENT_APP1

public static final byte SEGMENT_APP1

APP1 Jpeg segment identifier -- where Exif data is kept.

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Constant Field Values

SEGMENT_APP2

public static final byte SEGMENT_APP2

APP2 Jpeg segment identifier.

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Constant Field Values

SEGMENT_APP3

public static final byte SEGMENT_APP3

APP3 Jpeg segment identifier.

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Constant Field Values

SEGMENT_APP4

public static final byte SEGMENT_APP4

APP4 Jpeg segment identifier.

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Constant Field Values

SEGMENT_APP5

public static final byte SEGMENT_APP5

APP5 Jpeg segment identifier.

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Constant Field Values

SEGMENT_APP6

public static final byte SEGMENT_APP6

APP6 Jpeg segment identifier.

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Constant Field Values

SEGMENT_APP7

public static final byte SEGMENT_APP7

APP7 Jpeg segment identifier.

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Constant Field Values

SEGMENT_APP8

public static final byte SEGMENT_APP8

APP8 Jpeg segment identifier.

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Constant Field Values

SEGMENT_APP9

public static final byte SEGMENT_APP9

APP9 Jpeg segment identifier.

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Constant Field Values

SEGMENT_APPA

public static final byte SEGMENT_APPA

APPA Jpeg segment identifier -- can hold Unicode comments.

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Constant Field Values

SEGMENT_APPB

public static final byte SEGMENT_APPB

APPB Jpeg segment identifier.

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Constant Field Values

SEGMENT_APPC

public static final byte SEGMENT_APPC

APPC Jpeg segment identifier.

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Constant Field Values

SEGMENT_APPD

public static final byte SEGMENT_APPD

APPD Jpeg segment identifier -- IPTC data in here.

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Constant Field Values

SEGMENT_APPE

public static final byte SEGMENT_APPE

APPE Jpeg segment identifier.

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Constant Field Values

SEGMENT_APPF

public static final byte SEGMENT_APPF

APPF Jpeg segment identifier.

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Constant Field Values

SEGMENT_SOI

public static final byte SEGMENT_SOI

Start Of Image segment identifier.

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Constant Field Values

SEGMENT_DQT

public static final byte SEGMENT_DQT

Define Quantization Table segment identifier.

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Constant Field Values

SEGMENT_DHT

public static final byte SEGMENT_DHT

Define Huffman Table segment identifier.

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Constant Field Values

SEGMENT_SOF0

public static final byte SEGMENT_SOF0

Start-of-Frame Zero segment identifier.

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Constant Field Values

SEGMENT_COM

public static final byte SEGMENT_COM

Jpeg comment segment identifier.

See Also:

Constant Field Values

Constructor Detail

JpegSegmentReader

public JpegSegmentReader(File file)
                  throws JpegProcessingException

Creates a JpegSegmentReader for a specific file.

Parameters:

file - the Jpeg file to read segments from

Throws:

JpegProcessingException

JpegSegmentReader

public JpegSegmentReader(byte[] fileContents)
                  throws JpegProcessingException

Creates a JpegSegmentReader for a byte array.

Parameters:

fileContents - the byte array containing Jpeg data

Throws:

JpegProcessingException

JpegSegmentReader

public JpegSegmentReader(InputStream in)
                  throws JpegProcessingException

Creates a JpegSegmentReader for an InputStream.

Parameters:

in - the InputStream containing Jpeg data

Throws:

JpegProcessingException

JpegSegmentReader

public JpegSegmentReader(JpegSegmentData segmentData)

Creates a JpegSegmentReader for a JpegSegmentData.

Parameters:

segmentData - an object containing prepared JPEG segment data.

Method Detail

readSegment

public byte[] readSegment(byte segmentMarker)
                   throws JpegProcessingException

Reads the first instance of a given Jpeg segment, returning the contents as a byte array.

Parameters:

segmentMarker - the byte identifier for the desired segment

Returns:

the byte array if found, else null

Throws:

JpegProcessingException - for any problems processing the Jpeg data, including inner IOExceptions

readSegment

public byte[] readSegment(byte segmentMarker,
                          int occurrence)

Reads the first instance of a given Jpeg segment, returning the contents as a byte array.

Parameters:

segmentMarker - the byte identifier for the desired segment

occurrence - the occurrence of the specified segment within the jpeg file

Returns:

the byte array if found, else null

getSegmentCount

public final int getSegmentCount(byte segmentMarker)

Returns the number of segments having the specified JPEG segment marker.

Parameters:

segmentMarker - the JPEG segment identifying marker.

Returns:

the count of matching segments.

getSegmentData

public final JpegSegmentData getSegmentData()

Returns the JpegSegmentData object used by this reader.

Returns:

the JpegSegmentData object.

readSegments

private void readSegments()
                   throws JpegProcessingException

Throws:

JpegProcessingException

getJpegInputStream

private BufferedInputStream getJpegInputStream()
                                        throws JpegProcessingException

Private helper method to create a BufferedInputStream of Jpeg data from whichever data source was specified upon construction of this instance.

Returns:

a a BufferedInputStream of Jpeg data

Throws:

JpegProcessingException - for any problems obtaining the stream

isValidJpegHeaderBytes

private boolean isValidJpegHeaderBytes(InputStream fileStream)
                                throws IOException

Helper method that validates the Jpeg file's magic number.

Parameters:

fileStream - the InputStream to read bytes from, which must be positioned at its start (i.e. no bytes read yet)

Returns:

true if the magic number is Jpeg (0xFFD8)

Throws:

IOException - for any problem in reading the file