itextpdf.jar is a component in iText 5 Java library to provide core functionalities. iText Java library allows you to generate and manage PDF documents.

The Source Code files are provided at iText GitHub site.

You can compile it to generate your JAR file, using pom.xml as the build configuration file.

The source code of itextpdf-5.5.14.jar is provided below:

⏎ com/itextpdf/text/pdf/PdfStructTreeController.java

/*
 *
 * This file is part of the iText (R) project.
    Copyright (c) 1998-2020 iText Group NV
 * Authors: Bruno Lowagie, Eugene Markovskyi, et al.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License version 3
 * as published by the Free Software Foundation with the addition of the
 * following permission added to Section 15 as permitted in Section 7(a):
 * FOR ANY PART OF THE COVERED WORK IN WHICH THE COPYRIGHT IS OWNED BY
 * ITEXT GROUP. ITEXT GROUP DISCLAIMS THE WARRANTY OF NON INFRINGEMENT
 * OF THIRD PARTY RIGHTS
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU Affero General Public License for more details.
 * You should have received a copy of the GNU Affero General Public License
 * along with this program; if not, see http://www.gnu.org/licenses or write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA, 02110-1301 USA, or download the license from the following URL:
 * http://itextpdf.com/terms-of-use/
 *
 * The interactive user interfaces in modified source and object code versions
 * of this program must display Appropriate Legal Notices, as required under
 * Section 5 of the GNU Affero General Public License.
 *
 * In accordance with Section 7(b) of the GNU Affero General Public License,
 * a covered work must retain the producer line in every PDF that is created
 * or manipulated using iText.
 *
 * You can be released from the requirements of the license by purchasing
 * a commercial license. Buying such a license is mandatory as soon as you
 * develop commercial activities involving the iText software without
 * disclosing the source code of your own applications.
 * These activities include: offering paid services to customers as an ASP,
 * serving PDFs on the fly in a web application, shipping iText with a closed
 * source product.
 *
 * For more information, please contact iText Software Corp. at this
 * address: sales@itextpdf.com
 */
package com.itextpdf.text.pdf;

import com.itextpdf.text.error_messages.MessageLocalization;
import com.itextpdf.text.log.LoggerFactory;
import com.itextpdf.text.log.Logger;

import java.io.IOException;
import java.util.Map;

public class PdfStructTreeController {

    private PdfDictionary structTreeRoot;
    private PdfCopy writer;
    private PdfStructureTreeRoot structureTreeRoot;
    private PdfDictionary parentTree;
    protected PdfReader reader;
    private PdfDictionary roleMap = null;
    private PdfDictionary sourceRoleMap = null;
    private PdfDictionary sourceClassMap = null;
    private PdfIndirectReference nullReference = null;
//    private HashSet<Integer> openedDocuments = new HashSet<Integer>();

    public static enum returnType {BELOW, FOUND, ABOVE, NOTFOUND};

    protected PdfStructTreeController(PdfReader reader, PdfCopy writer) throws BadPdfFormatException {
        if (!writer.isTagged())
            throw new BadPdfFormatException(MessageLocalization.getComposedMessage("no.structtreeroot.found"));
        this.writer = writer;
        structureTreeRoot = writer.getStructureTreeRoot();
        structureTreeRoot.put(PdfName.PARENTTREE, new PdfDictionary(PdfName.STRUCTELEM));
        setReader(reader);
    }

    protected void setReader(PdfReader reader) throws BadPdfFormatException {
        this.reader = reader;
        PdfObject obj = reader.getCatalog().get(PdfName.STRUCTTREEROOT);
        obj = getDirectObject(obj);
        if ((obj == null) || (!obj.isDictionary()))
            throw new BadPdfFormatException(MessageLocalization.getComposedMessage("no.structtreeroot.found"));
        structTreeRoot = (PdfDictionary) obj;
        obj = PdfStructTreeController.getDirectObject(structTreeRoot.get(PdfName.PARENTTREE));
        if (obj == null || !obj.isDictionary())
            throw new BadPdfFormatException(MessageLocalization.getComposedMessage("the.document.does.not.contain.parenttree"));
        parentTree = (PdfDictionary) obj;
        sourceRoleMap = null;
        sourceClassMap = null;
        nullReference = null;
    }

    static public boolean checkTagged(PdfReader reader) {
        PdfObject obj = reader.getCatalog().get(PdfName.STRUCTTREEROOT);
        obj = getDirectObject(obj);
        if (obj == null || !obj.isDictionary())
            return false;
        PdfDictionary structTreeRoot = (PdfDictionary) obj;
        obj = PdfStructTreeController.getDirectObject(structTreeRoot.get(PdfName.PARENTTREE));
        if (obj == null || !obj.isDictionary())
            return false;
        return true;
    }

    public static PdfObject getDirectObject(PdfObject object) {
        if (object == null)
            return null;
        while (object.isIndirect())
            object = PdfReader.getPdfObjectRelease(object);
        return object;
    }

    public void copyStructTreeForPage(PdfNumber sourceArrayNumber, int newArrayNumber) throws BadPdfFormatException, IOException {
//        int documentHash = getDocumentHash(reader);
//        if (!openedDocuments.contains(documentHash)) {
//            openedDocuments.add(documentHash);
//
//        }
        if (copyPageMarks(parentTree, sourceArrayNumber, newArrayNumber) == returnType.NOTFOUND) {
            throw new BadPdfFormatException(MessageLocalization.getComposedMessage("invalid.structparent"));
        }
    }

    private returnType copyPageMarks(PdfDictionary parentTree, PdfNumber arrayNumber, int newArrayNumber) throws BadPdfFormatException, IOException {
        PdfArray pages = (PdfArray) getDirectObject(parentTree.get(PdfName.NUMS));
        if (pages == null) {
            PdfArray kids = (PdfArray) getDirectObject(parentTree.get(PdfName.KIDS));
            if (kids == null)
                return returnType.NOTFOUND;
            int cur = kids.size() / 2;
            int begin = 0;
            while (true) {
                PdfDictionary kidTree = (PdfDictionary) getDirectObject(kids.getPdfObject(cur + begin));
                switch (copyPageMarks(kidTree, arrayNumber, newArrayNumber)) {
                    case FOUND:
                        return returnType.FOUND;
                    case ABOVE:
                        begin += cur;
                        cur /= 2;
                        if (cur == 0)
                            cur = 1;
                        if (cur + begin == kids.size())
                            return returnType.ABOVE;
                        break;
                    case BELOW:
                        if (cur + begin == 0)
                            return returnType.BELOW;
                        if (cur == 0)
                            return returnType.NOTFOUND;
                        cur /= 2;
                        break;
                    default:
                        return returnType.NOTFOUND;
                }
            }
        } else {
            if (pages.size() == 0)
                return returnType.NOTFOUND;
            return findAndCopyMarks(pages, arrayNumber.intValue(), newArrayNumber);
        }
    }

    private returnType findAndCopyMarks(PdfArray pages, int arrayNumber, int newArrayNumber) throws BadPdfFormatException, IOException {
        if (pages.getAsNumber(0).intValue() > arrayNumber)
            return returnType.BELOW;
        if (pages.getAsNumber(pages.size() - 2).intValue() < arrayNumber)
            return returnType.ABOVE;
        int cur = pages.size() / 4;
        int begin = 0;
        int curNumber;

        while (true) {
            curNumber = pages.getAsNumber((begin + cur) * 2).intValue();
            if (curNumber == arrayNumber) {
                PdfObject obj = pages.getPdfObject((begin + cur) * 2 + 1);
                PdfObject obj1 = obj;
                while (obj.isIndirect()) obj = PdfReader.getPdfObjectRelease(obj);
                if (obj.isArray()) {
                    PdfObject firstNotNullKid = null;
                    for (PdfObject numObj: (PdfArray)obj){
                        if (numObj.isNull()) {
                            if (nullReference == null)
                                nullReference = writer.addToBody(new PdfNull()).getIndirectReference();
                            structureTreeRoot.setPageMark(newArrayNumber, nullReference);
                        } else {
                            PdfObject res = writer.copyObject(numObj, true, false);
                            if (firstNotNullKid == null) firstNotNullKid = res;
                            structureTreeRoot.setPageMark(newArrayNumber, (PdfIndirectReference) res);
                        }
                    }
                    attachStructTreeRootKids(firstNotNullKid);
                } else if (obj.isDictionary()) {
                    PdfDictionary k = getKDict((PdfDictionary)obj);
                    if (k == null)
                        return returnType.NOTFOUND;
                    PdfObject res = writer.copyObject(obj1, true, false);
                    structureTreeRoot.setAnnotationMark(newArrayNumber, (PdfIndirectReference)res);
                } else
                    return returnType.NOTFOUND;
                return returnType.FOUND;
            }
            if (curNumber < arrayNumber) {
                if (cur == 0)
                    return returnType.NOTFOUND;
                begin += cur;
                if (cur != 1)
                    cur /= 2;
                if (cur + begin == pages.size())
                    return returnType.NOTFOUND;
                continue;
            }
            if (cur + begin == 0)
                return returnType.BELOW;
            if (cur == 0)
                return returnType.NOTFOUND;
            cur /= 2;
        }
    }

    /**
     * Add kid to structureTreeRoot from structTreeRoot
     */
    protected void attachStructTreeRootKids(PdfObject firstNotNullKid) throws IOException, BadPdfFormatException {
        PdfObject structKids = structTreeRoot.get(PdfName.K);
        if (structKids == null || (!structKids.isArray() && !structKids.isIndirect())) {
            // incorrect syntax of tags
            addKid(structureTreeRoot, firstNotNullKid);
        } else {
            if (structKids.isIndirect()) {
                addKid(structKids);
            } else { //structKids.isArray()
                for (PdfObject kid: (PdfArray)structKids)
                    addKid(kid);
            }
        }
    }

    static PdfDictionary getKDict(PdfDictionary obj) {
        PdfDictionary k = obj.getAsDict(PdfName.K);
        if (k != null) {
            if (PdfName.OBJR.equals(k.getAsName(PdfName.TYPE))) {
                return k;
            }
        } else {
            PdfArray k1 = obj.getAsArray(PdfName.K);
            if (k1 == null)
                return null;
            for (int i = 0; i < k1.size(); i++) {
                k = k1.getAsDict(i);
                if (k != null) {
                    if (PdfName.OBJR.equals(k.getAsName(PdfName.TYPE))) {
                        return k;
                    }
                }
            }
        }
        return null;
    }

    private void addKid(PdfObject obj) throws IOException, BadPdfFormatException {
        if (!obj.isIndirect()) return;
        PRIndirectReference currRef = (PRIndirectReference)obj;
        RefKey key =  new RefKey(currRef);
        if (!writer.indirects.containsKey(key)) {
            writer.copyIndirect(currRef, true, false);
        }
        PdfIndirectReference newKid = writer.indirects.get(key).getRef();

        if (writer.updateRootKids) {
            addKid(structureTreeRoot, newKid);
            writer.structureTreeRootKidsForReaderImported(reader);
        }
    }

    private static PdfArray getDirectArray(PdfArray in) {
        PdfArray out = new PdfArray();
        for (int i = 0; i < in.size(); ++i) {
            PdfObject value = getDirectObject(in.getPdfObject(i));
            if (value == null)
                continue;
            if (value.isArray()) {
                out.add(getDirectArray((PdfArray) value));
            } else if (value.isDictionary()) {
                out.add(getDirectDict((PdfDictionary) value));
            } else {
                out.add(value);
            }
        }
        return out;
    }

    private static PdfDictionary getDirectDict(PdfDictionary in) {
        PdfDictionary out = new PdfDictionary();
        for (Map.Entry<PdfName, PdfObject> entry : in.hashMap.entrySet()) {
            PdfObject value = getDirectObject(entry.getValue());
            if (value == null)
                continue;
            if (value.isArray()) {
                out.put(entry.getKey(), getDirectArray((PdfArray) value));
            } else if (value.isDictionary()) {
                out.put(entry.getKey(), getDirectDict((PdfDictionary) value));
            } else {
                out.put(entry.getKey(), value);
            }
        }
        return out;
    }

    public static boolean compareObjects(PdfObject value1, PdfObject value2) {
        value2 = getDirectObject(value2);
        if (value2 == null)
            return false;
        if (value1.type() != value2.type())
            return false;

        if (value1.isBoolean()) {
            if (value1 == value2)
                return true;
            if (value2 instanceof PdfBoolean) {
                return ((PdfBoolean) value1).booleanValue() == ((PdfBoolean) value2).booleanValue();
            }
            return false;
        } else if (value1.isName()) {
            return value1.equals(value2);
        } else if (value1.isNumber()) {
            if (value1 == value2)
                return true;
            if (value2 instanceof PdfNumber) {
                return ((PdfNumber) value1).doubleValue() == ((PdfNumber) value2).doubleValue();
            }
            return false;
        } else if (value1.isNull()) {
            if (value1 == value2)
                return true;
            if (value2 instanceof PdfNull)
                return true;
            return false;
        } else if (value1.isString()) {
            if (value1 == value2)
                return true;
            if (value2 instanceof PdfString) {
                return ((((PdfString) value2).value == null && ((PdfString) value1).value == null)
                        || (((PdfString) value1).value != null && ((PdfString) value1).value.equals(((PdfString) value2).value)));
            }
            return false;
        }
        if (value1.isArray()) {
            PdfArray array1 = (PdfArray) value1;
            PdfArray array2 = (PdfArray) value2;
            if (array1.size() != array2.size())
                return false;
            for (int i = 0; i < array1.size(); ++i)
                if (!compareObjects(array1.getPdfObject(i), array2.getPdfObject(i)))
                    return false;
            return true;
        }
        if (value1.isDictionary()) {
            PdfDictionary first = (PdfDictionary) value1;
            PdfDictionary second = (PdfDictionary) value2;
            if (first.size() != second.size())
                return false;
            for (PdfName name : first.hashMap.keySet()) {
                if (!compareObjects(first.get(name), second.get(name)))
                    return false;
            }
            return true;
        }
        return false;
    }

    protected void addClass(PdfObject object) throws BadPdfFormatException {
        object = getDirectObject(object);
        if (object.isDictionary()) {
            PdfObject curClass = ((PdfDictionary) object).get(PdfName.C);
            if (curClass == null)
                return;
            if (curClass.isArray()) {
                PdfArray array = (PdfArray) curClass;
                for (int i = 0; i < array.size(); ++i) {
                    addClass(array.getPdfObject(i));
                }
            } else if (curClass.isName())
                addClass(curClass);
        } else if (object.isName()) {
            PdfName name = (PdfName) object;
            if (sourceClassMap == null) {
                object = getDirectObject(structTreeRoot.get(PdfName.CLASSMAP));
                if (object == null || !object.isDictionary()) {
                    return;
                }
                sourceClassMap = (PdfDictionary) object;
            }
            object = getDirectObject(sourceClassMap.get(name));
            if (object == null) {
                return;
            }
            PdfObject put = structureTreeRoot.getMappedClass(name);
            if (put != null) {
                if (!compareObjects(put, object)) {
                    throw new BadPdfFormatException(MessageLocalization.getComposedMessage("conflict.in.classmap", name));
                }
            } else {
                if (object.isDictionary())
                    structureTreeRoot.mapClass(name, getDirectDict((PdfDictionary) object));
                else if (object.isArray()) {
                    structureTreeRoot.mapClass(name, getDirectArray((PdfArray) object));
                }
            }
        }
    }

    protected void addRole(PdfName structType) throws BadPdfFormatException {
        if (structType == null) {
            return;
        }
        for (PdfName name : writer.getStandardStructElems()) {
            if (name.equals(structType))
                return;
        }
        if (sourceRoleMap == null) {
            PdfObject object = getDirectObject(structTreeRoot.get(PdfName.ROLEMAP));
            if (object == null || !object.isDictionary()) {
                return;
            }
            sourceRoleMap = (PdfDictionary) object;
        }
        PdfObject object = sourceRoleMap.get(structType);
        if (object == null || !object.isName()) {
            return;
        }
        PdfObject currentRole;
        if (roleMap == null) {
            roleMap = new PdfDictionary();
            structureTreeRoot.put(PdfName.ROLEMAP, roleMap);
            roleMap.put(structType, object);
        } else if ((currentRole = roleMap.get(structType)) != null) {
            if (!currentRole.equals(object)) {
                throw new BadPdfFormatException(MessageLocalization.getComposedMessage("conflict.in.rolemap", structType));
            }
        } else {
            roleMap.put(structType, object);
        }
    }

    protected void addKid(PdfDictionary parent, PdfObject kid) {
        PdfObject kidObj = parent.get(PdfName.K);
        PdfArray kids;
        if (kidObj instanceof PdfArray) {
            kids = (PdfArray) kidObj;
        } else {
            kids = new PdfArray();
            if (kidObj != null)
                kids.add(kidObj);
        }
        kids.add(kid);
        parent.put(PdfName.K, kids);
    }

//    private int getDocumentHash(final PdfReader reader) {
//        PdfDictionary trailer = reader.trailer;
//        int hash = trailer.size();
//        HashMap<String, String> info = reader.getInfo();
//        PdfArray id = trailer.getAsArray(PdfName.ID);
//        if (id != null) {
//            for (PdfObject idPart : id) {
//                if (idPart instanceof PdfString) {
//                    hash = hash ^ ((PdfString)idPart).toUnicodeString().hashCode();
//                }
//            }
//        }
//        for (String key : info.keySet()) {
//            String value = info.get(key);
//            if (value != null) {
//                hash = hash ^ key.hashCode() ^ value.hashCode();
//            }
//        }
//        return hash;
//    }

}

⏎ com/itextpdf/text/pdf/PdfStructTreeController.java

Or download all of them as a single archive file:

File name: itextpdf-5.5.14-fyi.zip
File size: 2163839 bytes
Release date: 2009-10-09
Download 

⇒ iText-2.1.6.jar - iText, a JAVA-PDF library

⇐ iText layout.jar Source Code

⇑ Download and Install iText Java Library

⇑⇑ iText for PDF Generation