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/IOP/ExceptionDetailMessage.java

package org.omg.IOP;


/**
* org/omg/IOP/ExceptionDetailMessage.java .
* Generated by the IDL-to-Java compiler (portable), version "3.2"
* from c:/re/workspace/8-2-build-windows-amd64-cygwin/jdk8u191/11896/corba/src/share/classes/org/omg/PortableInterceptor/IOP.idl
* Saturday, October 6, 2018 9:30:42 AM PDT
*/

public interface ExceptionDetailMessage
{

  /**
     * CORBA formal/02-06-01: 13.7.1:
     * ExceptionDetailMessage identifies a CDR encapsulation of a wstring,
     * encoded using GIOP 1.2 with a TCS-W of UTF-16.  This service context
     * may be sent on Reply messages with a reply_status of SYSTEM_EXCEPTION
     * or USER_EXCEPTION. The usage of this service context is defined
     * by language mappings. <br/> <br/>
     *
     * IDL/Java: ptc/02-01-22: 1.15.2: 
     * When a System Exception is marshaled, its GIOP Reply message shall
     * include an associated ExceptionDetailMessage service context. The
     * callee's stack trace is often very valuable debugging information but
     * may contain sensitive or unwanted information. The wstring within the
     * service context will therefore contain additional information relating
     * to the exception, for example the result of calling either
     * printStackTrace(PrintWriter) or getMessage() on the exception. When
     * unmarshaling a System Exception on the client side, the wstring from
     * any ExceptionDetailMessage service context shall become the Java error
     * message in the unmarshaled exception object.
     */
  public static final int value = (int)(14L);
}

⏎ org/omg/IOP/ExceptionDetailMessage.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)