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 java.* package in JRE 1.8.0_191 rt.jar. Java source codes are also provided.

⏎ java/rmi/UnmarshalException.java

/*
 * Copyright (c) 1996, 1998, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package java.rmi;

/**
 * An <code>UnmarshalException</code> can be thrown while unmarshalling the
 * parameters or results of a remote method call if any of the following
 * conditions occur:
 * <ul>
 * <li> if an exception occurs while unmarshalling the call header
 * <li> if the protocol for the return value is invalid
 * <li> if a <code>java.io.IOException</code> occurs unmarshalling
 * parameters (on the server side) or the return value (on the client side).
 * <li> if a <code>java.lang.ClassNotFoundException</code> occurs during
 * unmarshalling parameters or return values
 * <li> if no skeleton can be loaded on the server-side; note that skeletons
 * are required in the 1.1 stub protocol, but not in the 1.2 stub protocol.
 * <li> if the method hash is invalid (i.e., missing method).
 * <li> if there is a failure to create a remote reference object for
 * a remote object's stub when it is unmarshalled.
 * </ul>
 *
 * @author  Ann Wollrath
 * @since   JDK1.1
 */
public class UnmarshalException extends RemoteException {

    /* indicate compatibility with JDK 1.1.x version of class */
    private static final long serialVersionUID = 594380845140740218L;

    /**
     * Constructs an <code>UnmarshalException</code> with the specified
     * detail message.
     *
     * @param s the detail message
     * @since JDK1.1
     */
    public UnmarshalException(String s) {
        super(s);
    }

    /**
     * Constructs an <code>UnmarshalException</code> with the specified
     * detail message and nested exception.
     *
     * @param s the detail message
     * @param ex the nested exception
     * @since JDK1.1
     */
    public UnmarshalException(String s, Exception ex) {
        super(s, ex);
    }
}

⏎ java/rmi/UnmarshalException.java

Or download all of them as a single archive file:

File name: jre-rt-java-1.8.0_191-src.zip
File size: 6664831 bytes
Release date: 2018-10-28
Download 

⇒ JRE 8 rt.jar - javax.* Package Source Code

⇐ JRE 8 plugin.jar - Java Deploy Control Panel Plugin

⇑ Download and Use JDK 8

⇑⇑ FAQ for JDK (Java Development Kit)