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/spec/EncodedKeySpec.java

/*
 * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package java.security.spec;

/**
 * This class represents a public or private key in encoded format.
 *
 * @author Jan Luehe
 *
 *
 * @see java.security.Key
 * @see java.security.KeyFactory
 * @see KeySpec
 * @see X509EncodedKeySpec
 * @see PKCS8EncodedKeySpec
 *
 * @since 1.2
 */

public abstract class EncodedKeySpec implements KeySpec {

    private byte[] encodedKey;

    /**
     * Creates a new EncodedKeySpec with the given encoded key.
     *
     * @param encodedKey the encoded key. The contents of the
     * array are copied to protect against subsequent modification.
     * @exception NullPointerException if {@code encodedKey}
     * is null.
     */
    public EncodedKeySpec(byte[] encodedKey) {
        this.encodedKey = encodedKey.clone();
    }

    /**
     * Returns the encoded key.
     *
     * @return the encoded key. Returns a new array each time
     * this method is called.
     */
    public byte[] getEncoded() {
        return this.encodedKey.clone();
    }

    /**
     * Returns the name of the encoding format associated with this
     * key specification.
     *
     * <p>If the opaque representation of a key
     * (see {@link java.security.Key Key}) can be transformed
     * (see {@link java.security.KeyFactory KeyFactory})
     * into this key specification (or a subclass of it),
     * {@code getFormat} called
     * on the opaque key returns the same value as the
     * {@code getFormat} method
     * of this key specification.
     *
     * @return a string representation of the encoding format.
     */
    public abstract String getFormat();
}

⏎ java/security/spec/EncodedKeySpec.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)