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

⏎ org/omg/CORBA/UnknownUserException.java

/*
 * Copyright (c) 1997, 2010, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package org.omg.CORBA;

/**
 * A class that contains user exceptions returned by the server.
 * When the client uses the DII to make an invocation, any user exception
 * returned from the server is enclosed in an <code>Any</code> object contained in the
 * <code>UnknownUserException</code> object. This is available from the
 * <code>Environment</code> object returned by the method <code>Request.env</code>.
 *
 * @see <A href="../../../../technotes/guides/idl/jidlExceptions.html">documentation on
 * Java&nbsp;IDL exceptions</A>
 * @see Request
 */

public final class UnknownUserException extends UserException {

    /** The <code>Any</code> instance that contains the actual user exception thrown
     *  by the server.
     * @serial
     */
    public Any except;

    /**
     * Constructs an <code>UnknownUserException</code> object.
     */
    public UnknownUserException() {
        super();
    }

    /**
     * Constructs an <code>UnknownUserException</code> object that contains the given
     * <code>Any</code> object.
     *
     * @param a an <code>Any</code> object that contains a user exception returned
     *         by the server
     */
    public UnknownUserException(Any a) {
        super();
        except = a;
    }
}

⏎ org/omg/CORBA/UnknownUserException.java

Or download all of them as a single archive file:

File name: jre-rt-org-1.8.0_191-src.zip
File size: 951125 bytes
Release date: 2018-10-28
Download 

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

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

⇑ Download and Use JDK 8

⇑⇑ FAQ for JDK (Java Development Kit)