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

⏎ java/security/KeyManagementException.java

/*
 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package java.security;

/**
 * This is the general key management exception for all operations
 * dealing with key management. Examples of subclasses of
 * KeyManagementException that developers might create for
 * giving more detailed information could include:
 *
 * <ul>
 * <li>KeyIDConflictException
 * <li>KeyAuthorizationFailureException
 * <li>ExpiredKeyException
 * </ul>
 *
 * @author Benjamin Renaud
 *
 * @see Key
 * @see KeyException
 */

public class KeyManagementException extends KeyException {

    private static final long serialVersionUID = 947674216157062695L;

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

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

    /**
     * Creates a {@code KeyManagementException} with the specified
     * detail message and cause.
     *
     * @param message the detail message (which is saved for later retrieval
     *        by the {@link #getMessage()} method).
     * @param cause the cause (which is saved for later retrieval by the
     *        {@link #getCause()} method).  (A {@code null} value is permitted,
     *        and indicates that the cause is nonexistent or unknown.)
     * @since 1.5
     */
    public KeyManagementException(String message, Throwable cause) {
        super(message, cause);
    }

    /**
     * Creates a {@code KeyManagementException} with the specified cause
     * and a detail message of {@code (cause==null ? null : cause.toString())}
     * (which typically contains the class and detail message of
     * {@code cause}).
     *
     * @param cause the cause (which is saved for later retrieval by the
     *        {@link #getCause()} method).  (A {@code null} value is permitted,
     *        and indicates that the cause is nonexistent or unknown.)
     * @since 1.5
     */
    public KeyManagementException(Throwable cause) {
        super(cause);
    }
}

⏎ java/security/KeyManagementException.java

Or download all of them as a single archive file:

File name: jre-rt-java-1.8.0_191-src.zip
File size: 6664831 bytes
Release date: 2018-10-28
Download 

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

⇐ JRE 8 plugin.jar - Java Deploy Control Panel Plugin

⇑ Download and Use JDK 8

⇑⇑ FAQ for JDK (Java Development Kit)