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

⏎ javax/naming/CommunicationException.java

/*
 * Copyright (c) 1999, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package javax.naming;

/**
  * This exception is thrown when the client is
  * unable to communicate with the directory or naming service.
  * The inability to communicate with the service might be a result
  * of many factors, such as network partitioning, hardware or interface problems,
  * failures on either the client or server side.
  * This exception is meant to be used to capture such communication problems.
  * <p>
  * Synchronization and serialization issues that apply to NamingException
  * apply directly here.
  *
  * @author Rosanna Lee
  * @author Scott Seligman
  * @since 1.3
  */
public class CommunicationException extends NamingException {
    /**
     * Constructs a new instance of CommunicationException using the
     * arguments supplied.
     *
     * @param   explanation     Additional detail about this exception.
     * @see java.lang.Throwable#getMessage
     */
    public CommunicationException(String explanation) {
        super(explanation);
    }

    /**
      * Constructs a new instance of CommunicationException.
      */
    public CommunicationException() {
        super();
    }

    /**
     * Use serialVersionUID from JNDI 1.1.1 for interoperability
     */
    private static final long serialVersionUID = 3618507780299986611L;
}

⏎ javax/naming/CommunicationException.java

Or download all of them as a single archive file:

File name: jre-rt-javax-1.8.0_191-src.zip
File size: 5381005 bytes
Release date: 2018-10-28
Download 

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

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

⇑ Download and Use JDK 8

⇑⇑ FAQ for JDK (Java Development Kit)