JRE 8 rt.jar is the JAR file for JRE 8 RT (Runtime) libraries. JRE (Java Runtime) 8 is the runtime environment included in JDK 8. JRE 8 rt.jar libraries are divided into 6 packages:

com.* - Internal Oracle and Sun Microsystems libraries
java.* - Standard Java API libraries.
javax.* - Extended Java API libraries.
jdk.* -  JDK supporting libraries.
org.* - Third party libraries.
sun.* - Old libraries developed by Sun Microsystems.

JAR File Information:

Directory of C:\fyicenter\jdk-1.8.0_191\jre\lib
      63,596,151 rt.jar

Here is the list of Java classes of the com.* package in JRE 1.8.0_191 rt.jar. Java source codes are also provided.

⏎ com/sun/imageio/plugins/wbmp/WBMPMetadataFormat.java

/*
 * Copyright (c) 2003, 2004, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package com.sun.imageio.plugins.wbmp;

import java.util.Arrays;
import javax.imageio.ImageTypeSpecifier;
import javax.imageio.metadata.IIOMetadataFormat;
import javax.imageio.metadata.IIOMetadataFormatImpl;

public class WBMPMetadataFormat extends IIOMetadataFormatImpl {

    private static IIOMetadataFormat instance = null;

    private WBMPMetadataFormat() {
        super(WBMPMetadata.nativeMetadataFormatName,
              CHILD_POLICY_SOME);

        // root -> ImageDescriptor
        addElement("ImageDescriptor",
                   WBMPMetadata.nativeMetadataFormatName,
                   CHILD_POLICY_EMPTY);

        addAttribute("ImageDescriptor", "WBMPType",
                     DATATYPE_INTEGER, true, "0");

        addAttribute("ImageDescriptor", "Width",
                     DATATYPE_INTEGER, true, null,
                     "0", "65535", true, true);
        addAttribute("ImageDescriptor", "Height",
                     DATATYPE_INTEGER, true, null,
                     "1", "65535", true, true);
    }



    public boolean canNodeAppear(String elementName,
                                 ImageTypeSpecifier imageType) {
        return true;
    }

    public static synchronized IIOMetadataFormat getInstance() {
        if (instance == null) {
            instance = new WBMPMetadataFormat();
        }
        return instance;
    }
}

⏎ com/sun/imageio/plugins/wbmp/WBMPMetadataFormat.java

Or download all of them as a single archive file:

File name: jre-rt-com-1.8.0_191-src.zip
File size: 8099783 bytes
Release date: 2018-10-28
Download 

⇒ Backup JDK 8 Installation Directory

⇐ JRE 8 rt.jar - org.* Package Source Code

⇑ Download and Use JDK 8

⇑⇑ FAQ for JDK (Java Development Kit)