kernel.jar is a component in iText Java library to provide low-level functionalities. iText Java library allows you to generate and manage PDF documents.

The Source Code files are provided together with the JAR file in the binary packge like iText7-Core-7.1.4.zip. You can download it at iText 7 Core Download site.

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

The source code of kernel-7.1.4.jar is provided below:

⏎ com/itextpdf/kernel/ProductInfo.java

/*

  This file is part of the iText (R) project.
    Copyright (c) 1998-2018 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.kernel;

import java.io.Serializable;

/**
 * Describes an iText 7 add on. An add on should register itself to a PdfDocument object if it
 * wants to be included in the debugging information.
 */
public class ProductInfo implements Serializable {
    private static final long serialVersionUID = 2410734474798313936L;

    private String name;
    private int major;
    private int minor;
    private int patch;
    private boolean snapshot;

    /**
     * Instantiates a ProductInfo object.
     *
     * @param name      name of the add on
     * @param major     major version of the add on
     * @param minor     minor version of the add on
     * @param patch     patch number of the add on
     * @param snapshot  whether the version of this add on is a snapshot build or not
     */
    public ProductInfo(String name, int major, int minor, int patch, boolean snapshot) {
        this.name = name;
        this.major = major;
        this.minor = minor;
        this.patch = patch;
        this.snapshot = snapshot;
    }

    public String getName() {
        return name;
    }

    public int getMajor() {
        return major;
    }

    public int getMinor() {
        return minor;
    }

    public int getPatch() {
        return patch;
    }

    public boolean isSnapshot() {
        return snapshot;
    }

    @Override
    public String toString() {
        return name + "-" + major + "." + minor + "." + patch + ( snapshot ? "-SNAPSHOT" : "" );
    }

}

⏎ com/itextpdf/kernel/ProductInfo.java

Or download all of them as a single archive file:

File name: kernel-7.1.4-sources.jar
File size: 1201221 bytes
Release date: 2018-10-09
Download 

⇒ iText io.jar Source Code

⇐ Download and Install iText7-Core-7.1.4.zip

⇑ Download and Install iText Java Library

⇑⇑ iText for PDF Generation