org.icepdf.core.pobjects
Class PTrailer

java.lang.Object
  org.icepdf.core.pobjects.Dictionary
      org.icepdf.core.pobjects.PTrailer

public class PTrailer
extends Dictionary

The trailer of a PDF file enables an application reading the file to quickly find the cross-reference table and certain special objects. Applications should read a PDF file from its end. The last line of the file contains only the end-of-file marker, %%EOF.

A document can have more then one trailer reference. It is important to use the addTrailer() method if a subsequent trailer is found, or the addPreviousTrailer() method if a previous trailer is found, depending on if the PDF file is being read linearly, or via random access seeking.

If the Prev key entry is present then the document has more then one cross-reference section. There is a numerical value, which is typically associated with the trailer, that comes after startxref, and before %%EOF. It is byte offset from the beginning of the file to the beginning of the last cross-reference section.

In a regular PDF, it's the address of the current xref table. In a linearized PDF, it's the address of the xref table at the file beginning, or zero. In an updated PDF, it's the address of the current xref table. In all cases, the LastCrossReferenceSection field, at the end of the PDF file, points to the byte offset from the beginning of the file, of the "last" xref section, which means the xref section with the highest precedence. For each xref section, its following trailer section has a Prev field, which points to the byte offset from the beginning of the file, of the xref section with one less degree of precedence.

Since:

1.1

Field Summary

Fields inherited from class org.icepdf.core.pobjects.Dictionary

entries, inited, isDeleted, isNew, library, SUBTYPE_KEY, TYPE_KEY

Constructor Summary

PTrailer(Library library, java.util.Hashtable dictionary, CrossReference xrefTable, CrossReference xrefStream)
Create a new PTrailer object

Method Summary

protected void	addNextTrailer(PTrailer nextTrailer) Add the trailer dictionary to the current trailer object's dictionary.
protected void	addPreviousTrailer(PTrailer previousTrailer)
protected CrossReference	getCrossReferenceStream() Gets the cross reference stream.
protected CrossReference	getCrossReferenceTable() Gets the cross reference table.
java.util.Hashtable	getDictionary() Get the trailer object's dictionary.
java.util.Hashtable	getEncrypt() The document's encryption dictionary Required : if document is encrypted; PDF 1.1
java.util.Vector	getID() A vector of two strings constituting a file identifier Optional : PDF 1.1.
PInfo	getInfo() The document's information dictionary Optional : must be an indirect reference.
int	getNumberOfObjects() Gets the total number of entries in the file's cross-reference table, as defined by the combination of the original section and all updated sections.
long	getPosition()
long	getPrev() Gets the byte offset from the beginning of the file to the beginning of the previous cross-reference section.
protected CrossReference	getPrimaryCrossReference() Depending on if the PDF file is version 1.4 or before, or 1.5 or after, it may have a cross reference table, or cross reference stream, or both.
Catalog	getRootCatalog() Gets the Catalog entry for this PDF document.
Reference	getRootCatalogReference() Gets the catalog reference for the PDF document contained in the file.
protected void	loadXRefStmIfApplicable()
protected void	onDemandLoadAndSetupPreviousTrailer()
void	setPosition(long pos) After this PTrailer is parsed, we store it's location within the PDF here, for future use.
java.lang.String	toString() Returns a summary of the PTrailer dictionary values.

Methods inherited from class org.icepdf.core.pobjects.Dictionary

getEntries, getFloat, getInt, getLibrary, getNumber, getObject, getObject, getPObjectReference, init, isDeleted, isNew, setDeleted, setNew, setPObjectReference

Methods inherited from class java.lang.Object

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

Constructor Detail

PTrailer

public PTrailer(Library library,
                java.util.Hashtable dictionary,
                CrossReference xrefTable,
                CrossReference xrefStream)

Create a new PTrailer object

Parameters:

dictionary - dictionary associated with the trailer

Method Detail

getNumberOfObjects

public int getNumberOfObjects()

Gets the total number of entries in the file's cross-reference table, as defined by the combination of the original section and all updated sections. Equivalently, this value is 1 greater than the highest object number used in the file.

• Note: Any object in a cross-reference section whose number is greater than this value is ignored and considered missing.

Required : must not be an indirect reference

Returns:

total number of entries in the file's cross-reference table

getPrev

public long getPrev()

Gets the byte offset from the beginning of the file to the beginning of the previous cross-reference section.

(Present only if the file has more than one cross-reference section; must not be an indirect reference)

Returns:

byte offset from beginning of the file to the beginning of the previous cross-reference section

getPrimaryCrossReference

protected CrossReference getPrimaryCrossReference()

Depending on if the PDF file is version 1.4 or before, or 1.5 or after, it may have a cross reference table, or cross reference stream, or both. If there are both, then the cross reference table has precedence.

Returns:

the cross reference object with the highest precedence, for this trailer

getCrossReferenceTable

protected CrossReference getCrossReferenceTable()

Gets the cross reference table.

Returns:

cross reference table object; null, if one does not exist.

getCrossReferenceStream

protected CrossReference getCrossReferenceStream()

Gets the cross reference stream.

Returns:

cross reference stream object; null, if one does not exist.

getRootCatalogReference

public Reference getRootCatalogReference()

Gets the catalog reference for the PDF document contained in the file.

Required : must not be an indirect reference

Returns:

reference number of catalog reference.

getRootCatalog

public Catalog getRootCatalog()

Gets the Catalog entry for this PDF document.

Returns:

Catalog entry.

getEncrypt

public java.util.Hashtable getEncrypt()

The document's encryption dictionary

Required : if document is encrypted; PDF 1.1

Returns:

encryption dictionary

getInfo

public PInfo getInfo()

The document's information dictionary

Optional : must be an indirect reference.

Returns:

information dictionary

getID

public java.util.Vector getID()

A vector of two strings constituting a file identifier

Optional : PDF 1.1.

Returns:

vector containing constituting file identifier

getPosition

public long getPosition()

Returns:

The position in te file where this trailer is located

setPosition

public void setPosition(long pos)

After this PTrailer is parsed, we store it's location within the PDF here, for future use.

addNextTrailer

protected void addNextTrailer(PTrailer nextTrailer)

Add the trailer dictionary to the current trailer object's dictionary.

Parameters:

nextTrailer - document trailer object

addPreviousTrailer

protected void addPreviousTrailer(PTrailer previousTrailer)

onDemandLoadAndSetupPreviousTrailer

protected void onDemandLoadAndSetupPreviousTrailer()

loadXRefStmIfApplicable

protected void loadXRefStmIfApplicable()

getDictionary

public java.util.Hashtable getDictionary()

Get the trailer object's dictionary.

Returns:

dictionary

toString

public java.lang.String toString()

Returns a summary of the PTrailer dictionary values.

Overrides:

toString in class Dictionary

Returns:

dictionary values.