edu.harvard.hul.ois.jhove.module.pdf.ObjectStream Maven / Gradle / Ivy
/**********************************************************************
* Jhove - JSTOR/Harvard Object Validation Environment
* Copyright 2005 by JSTOR and the President and Fellows of Harvard College
**********************************************************************/
package edu.harvard.hul.ois.jhove.module.pdf;
import java.io.*;
import java.util.*;
/**
* This class implements the Object Stream, a new way of storing
* objects starting in PDF 1.4.
*
* An object stream can contain one or more objects, as described in
* Section 3.4 of the PostScript manual.
*
* 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
*
*/
public class ObjectStream {
private PdfStream _ostrm; // The underlying Stream object.
private PdfDictionary _dict;
private int _numObjects;
private int _firstOffset;
private Parser _parser;
private RandomAccessFile _raf;
/* Index of the object stream. Each element is an int[2],
* consisting of an object number and an offset.
*/
private Map _index;
/**
* Constructor.
*/
public ObjectStream(PdfStream ostrm, RandomAccessFile raf) {
_ostrm = ostrm;
_raf = raf;
_dict = ostrm.getDict ();
_parser = new Parser (new StreamTokenizer (raf, _ostrm.getStream()));
}
/** Checks the validity of the stream dictionary, and extracts
* information necessary for subsequent reading.
*/
public boolean isValid ()
{
try {
/* Type must be ObjStm */
PdfObject obj = _dict.get ("Type");
String typeStr = null;
if (obj instanceof PdfSimpleObject) {
typeStr = ((PdfSimpleObject) obj).getStringValue ();
}
if (!("ObjStm".equals (typeStr))) {
return false;
}
/* Number of objects */
obj = _dict.get ("N");
if (obj instanceof PdfSimpleObject) {
_numObjects = ((PdfSimpleObject) obj).getIntValue();
}
else {
return false;
}
/* Offset of first object */
obj = _dict.get ("First");
if (obj instanceof PdfSimpleObject) {
_firstOffset = ((PdfSimpleObject) obj).getIntValue();
}
else {
return false;
}
/* Optional refernce to object stream which this extends. */
obj = _dict.get ("Extends");
if (obj != null) {
/* What do we do with this? */
}
return true;
}
catch (Exception e) {
return false;
}
}
/** Reads the index of the object stream.
*/
public void readIndex ()
throws PdfException, IOException
{
Stream strm = _ostrm.getStream ();
strm.setFilters (_ostrm.getFilters ());
strm.initRead (_raf);
_index = new HashMap<> (_numObjects);
for (int i = 0; i < _numObjects; i++) {
/* If I'm reading it correctly, the numbers are
* encoded as ASCII strings separated by white space.
* I don't know what the restrictions, if any, are on
* the white space.
*/
Integer onum = new Integer (strm.readAsciiInt ());
Integer offset = new Integer (strm.readAsciiInt ());
_index.put (onum, offset);
}
}
/** Extracts an object from the stream. */
public PdfObject getObject (int objnum)
throws PdfException
{
Integer onum = Integer.valueOf(objnum);
Integer off = _index.get (onum);
try {
if (off != null) {
int offset = off.intValue ();
_parser.seek (offset + _firstOffset);
PdfObject object = _parser.readObject (false);
/* Need to ensure the object number is set */
object.setObjNumber(objnum);
return object;
}
return null;
}
catch (IOException e) {
throw new PdfMalformedException
(MessageConstants.PDF_HUL_16); // PDF-HUL-16
}
}
}