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/PdfNumberTree.java

/*
 *
 * This file is part of the iText (R) project.
    Copyright (c) 1998-2020 iText Group NV
 * Authors: Bruno Lowagie, Paulo Soares, 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 java.io.IOException;
import java.util.Arrays;
import java.util.HashMap;

/**
 * Creates a number tree.
 * @author Paulo Soares
 */
public class PdfNumberTree {

    private static final int leafSize = 64;

    /**
     * Creates a number tree.
     * @param items the item of the number tree. The key is an <CODE>Integer</CODE>
     * and the value is a <CODE>PdfObject</CODE>.
     * @param writer the writer
     * @throws IOException on error
     * @return the dictionary with the number tree.
     */
    public static <O extends PdfObject> PdfDictionary writeTree(HashMap<Integer, O> items, PdfWriter writer) throws IOException {
        if (items.isEmpty())
            return null;
        Integer numbers[] = new Integer[items.size()];
        numbers = items.keySet().toArray(numbers);
        Arrays.sort(numbers);
        if (numbers.length <= leafSize) {
            PdfDictionary dic = new PdfDictionary();
            PdfArray ar = new PdfArray();
            for (int k = 0; k < numbers.length; ++k) {
                ar.add(new PdfNumber(numbers[k].intValue()));
                ar.add(items.get(numbers[k]));
            }
            dic.put(PdfName.NUMS, ar);
            return dic;
        }
        int skip = leafSize;
        PdfIndirectReference kids[] = new PdfIndirectReference[(numbers.length + leafSize - 1) / leafSize];
        for (int k = 0; k < kids.length; ++k) {
            int offset = k * leafSize;
            int end = Math.min(offset + leafSize, numbers.length);
            PdfDictionary dic = new PdfDictionary();
            PdfArray arr = new PdfArray();
            arr.add(new PdfNumber(numbers[offset].intValue()));
            arr.add(new PdfNumber(numbers[end - 1].intValue()));
            dic.put(PdfName.LIMITS, arr);
            arr = new PdfArray();
            for (; offset < end; ++offset) {
                arr.add(new PdfNumber(numbers[offset].intValue()));
                arr.add(items.get(numbers[offset]));
            }
            dic.put(PdfName.NUMS, arr);
            kids[k] = writer.addToBody(dic).getIndirectReference();
        }
        int top = kids.length;
        while (true) {
            if (top <= leafSize) {
                PdfArray arr = new PdfArray();
                for (int k = 0; k < top; ++k)
                    arr.add(kids[k]);
                PdfDictionary dic = new PdfDictionary();
                dic.put(PdfName.KIDS, arr);
                return dic;
            }
            skip *= leafSize;
            int tt = (numbers.length + skip - 1 )/ skip;
            for (int k = 0; k < tt; ++k) {
                int offset = k * leafSize;
                int end = Math.min(offset + leafSize, top);
                PdfDictionary dic = new PdfDictionary();
                PdfArray arr = new PdfArray();
                arr.add(new PdfNumber(numbers[k * skip].intValue()));
                arr.add(new PdfNumber(numbers[Math.min((k + 1) * skip, numbers.length) - 1].intValue()));
                dic.put(PdfName.LIMITS, arr);
                arr = new PdfArray();
                for (; offset < end; ++offset) {
                    arr.add(kids[offset]);
                }
                dic.put(PdfName.KIDS, arr);
                kids[k] = writer.addToBody(dic).getIndirectReference();
            }
            top = tt;
        }
    }

    private static void iterateItems(PdfDictionary dic, HashMap<Integer, PdfObject> items) {
        PdfArray nn = (PdfArray)PdfReader.getPdfObjectRelease(dic.get(PdfName.NUMS));
        if (nn != null) {
            for (int k = 0; k < nn.size(); ++k) {
                PdfNumber s = (PdfNumber)PdfReader.getPdfObjectRelease(nn.getPdfObject(k++));
                items.put(Integer.valueOf(s.intValue()), nn.getPdfObject(k));
            }
        }
        else if ((nn = (PdfArray)PdfReader.getPdfObjectRelease(dic.get(PdfName.KIDS))) != null) {
            for (int k = 0; k < nn.size(); ++k) {
                PdfDictionary kid = (PdfDictionary)PdfReader.getPdfObjectRelease(nn.getPdfObject(k));
                iterateItems(kid, items);
            }
        }
    }

    public static HashMap<Integer, PdfObject> readTree(PdfDictionary dic) {
        HashMap<Integer, PdfObject> items = new HashMap<Integer, PdfObject>();
        if (dic != null)
            iterateItems(dic, items);
        return items;
    }
}

⏎ com/itextpdf/text/pdf/PdfNumberTree.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

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⇑ Download and Install iText Java Library

⇑⇑ iText for PDF Generation