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/corba/se/spi/activation/ServerIdHelper.java

package com.sun.corba.se.spi.activation;


/**
* com/sun/corba/se/spi/activation/ServerIdHelper.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/com/sun/corba/se/spi/activation/activation.idl
* Saturday, October 6, 2018 9:30:40 AM PDT
*/

abstract public class ServerIdHelper
{
  private static String  _id = "IDL:activation/ServerId:1.0";

  public static void insert (org.omg.CORBA.Any a, int that)
  {
    org.omg.CORBA.portable.OutputStream out = a.create_output_stream ();
    a.type (type ());
    write (out, that);
    a.read_value (out.create_input_stream (), type ());
  }

  public static int extract (org.omg.CORBA.Any a)
  {
    return read (a.create_input_stream ());
  }

  private static org.omg.CORBA.TypeCode __typeCode = null;
  synchronized public static org.omg.CORBA.TypeCode type ()
  {
    if (__typeCode == null)
    {
      __typeCode = org.omg.CORBA.ORB.init ().get_primitive_tc (org.omg.CORBA.TCKind.tk_long);
      __typeCode = org.omg.CORBA.ORB.init ().create_alias_tc (com.sun.corba.se.spi.activation.ServerIdHelper.id (), "ServerId", __typeCode);
    }
    return __typeCode;
  }

  public static String id ()
  {
    return _id;
  }

  public static int read (org.omg.CORBA.portable.InputStream istream)
  {
    int value = (int)0;
    value = istream.read_long ();
    return value;
  }

  public static void write (org.omg.CORBA.portable.OutputStream ostream, int value)
  {
    ostream.write_long (value);
  }

}

⏎ com/sun/corba/se/spi/activation/ServerIdHelper.java

⇒ Backup JDK 8 Installation Directory

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

⇑ Download and Use JDK 8

⇑⇑ FAQ for JDK (Java Development Kit)