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/xmp/options/package-info.java

/**
    <p>Package containing the option classes.</p>
    <p>These are used to configure diverse function calls of xmpcore:<p>
    <ul>
        <li>PropertyOptions - these are used to create properties and also to retrieve information about simple, array or struct properties, as well as qualifiers
        <li>ParseOptions - used to configure the parsing of xmp metadata packets
        <li>SerializationOptions - used to control the serialization of xmp metadata packets
        <li>AliasOptions - used by XMPSchemaRegistry#registerAlias()
        <li>IteratorOptions - used to set up an XMPIterator
        <li>Options - the base class of all option classes
    </ul>
 */
package com.itextpdf.kernel.xmp.options;

⏎ com/itextpdf/kernel/xmp/options/package-info.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