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/security/auth/DestroyFailedException.java

/*
 * Copyright (c) 1999, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package javax.security.auth;

/**
 * Signals that a {@code destroy} operation failed.
 *
 * <p> This exception is thrown by credentials implementing
 * the {@code Destroyable} interface when the {@code destroy}
 * method fails.
 *
 */
public class DestroyFailedException extends Exception {

    private static final long serialVersionUID = -7790152857282749162L;

    /**
     * Constructs a DestroyFailedException with no detail message. A detail
     * message is a String that describes this particular exception.
     */
    public DestroyFailedException() {
        super();
    }

    /**
     * Constructs a DestroyFailedException with the specified detail
     * message.  A detail message is a String that describes this particular
     * exception.
     *
     * <p>
     *
     * @param msg the detail message.
     */
    public DestroyFailedException(String msg) {
        super(msg);
    }
}

⏎ javax/security/auth/DestroyFailedException.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)