edu.harvard.hul.ois.jhove.module.pdf

Class CrossRefStream

java.lang.Object

edu.harvard.hul.ois.jhove.module.pdf.CrossRefStream

public class CrossRefStream
extends Object

This class implements the Cross-Reference Stream, an alternative to the Cross-Reference Table starting in PDF 1.4. A cross-reference stream is identified by a startxref keyword, as opposed to the xref keyword which identifies the old-style cross-reference table. JHOVE supports only FlateDecode as a filter for cross-reference streams. This is consistent with the implementation limitation described in Appendix H of the PDF manual for Acrobat 6 and earlier.

Author:

Gary McGath

Constructor Summary

Constructors

Constructor and Description
CrossRefStream(PdfStream xstrm) Constructor.

Method Summary

Modifier and Type	Method and Description
int	getContentStreamIndex() Returns the content stream index of the last object read.
int	getContentStreamObjNum() Returns the object number of the content stream in which this object is stored.
int	getCrossRefTableSize() Returns the total number of objects in the document's cross-reference table at the time this stream was written.
int	getFreeCount() Returns the number of free objects detected.
int	getObjNum() Returns number of the last object read by readNextObject ().
int	getOffset() Returns the offset of the last object read.
long	getPrevXref() Returns the offset of the previous cross-reference stream, or -1 if none is specified.
void	initRead(RandomAccessFile raf) Prepares for reading the Stream.
boolean	isObjCompressed() Returns true if the last object read by readNextObject () is a compressed object.
boolean	isValid() Returns true if the PdfStream object meets the requirements of a cross-reference stream.
boolean	readNextObject() Reads the next object in the stream.

Methods inherited from class java.lang.Object

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

Constructor Detail

CrossRefStream

public CrossRefStream(PdfStream xstrm)

Constructor.

Parameters:

xstrm - PdfStream object which contains a presumed cross-reference stream.

Method Detail

isValid

public boolean isValid()

Returns true if the PdfStream object meets the requirements of a cross-reference stream. Also extracts information from the dictionary for subsequent processing.

initRead

public void initRead(RandomAccessFile raf)
              throws IOException,
                     PdfException

Prepares for reading the Stream. If the filter list includes one which we don't support, throws a PdfException.

Throws:

IOException

PdfException

readNextObject

public boolean readNextObject()
                       throws IOException

Reads the next object in the stream. After calling readObject, it is possible to call accessors to get information about the object. For the moment, we punt on the question of how to deal with Object Streams. Free objects are skipped over while being counted. After readNextObject() returns false, the caller may call getFreeCount() to determine the number of free objects.

Returns:

true if there is an object, false if no more objects are available.

Throws:

IOException

getObjNum

public int getObjNum()

Returns number of the last object read by readNextObject (). Do not call if readNextObject () returns false.

isObjCompressed

public boolean isObjCompressed()

Returns true if the last object read by readNextObject () is a compressed object. Do not call if readNextObject () returns false.

getFreeCount

public int getFreeCount()

Returns the number of free objects detected. This may be called after readNextObject returns false, signifying that all the objects have been read and all the free objects counted.

getCrossRefTableSize

public int getCrossRefTableSize()

Returns the total number of objects in the document's cross-reference table at the time this stream was written.

getOffset

public int getOffset()

Returns the offset of the last object read. This is meaningful only if the last object read was type 1 (uncompressed).

getContentStreamObjNum

public int getContentStreamObjNum()

Returns the object number of the content stream in which this object is stored. This is meaningful only if the last object read was type 2 (compressed in content stream).

getPrevXref

public long getPrevXref()

Returns the offset of the previous cross-reference stream, or -1 if none is specified.

getContentStreamIndex

public int getContentStreamIndex()

Returns the content stream index of the last object read. This is meaningful only if the last object read was type 2 (compressed in content stream).