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/rmi/server/RMIFailureHandler.java

/*
 * Copyright (c) 1996, 1998, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package java.rmi.server;

/**
 * An <code>RMIFailureHandler</code> can be registered via the
 * <code>RMISocketFactory.setFailureHandler</code> call. The
 * <code>failure</code> method of the handler is invoked when the RMI
 * runtime is unable to create a <code>ServerSocket</code> to listen
 * for incoming calls. The <code>failure</code> method returns a boolean
 * indicating whether the runtime should attempt to re-create the
 * <code>ServerSocket</code>.
 *
 * @author      Ann Wollrath
 * @since       JDK1.1
 */
public interface RMIFailureHandler {

    /**
     * The <code>failure</code> callback is invoked when the RMI
     * runtime is unable to create a <code>ServerSocket</code> via the
     * <code>RMISocketFactory</code>. An <code>RMIFailureHandler</code>
     * is registered via a call to
     * <code>RMISocketFacotry.setFailureHandler</code>.  If no failure
     * handler is installed, the default behavior is to attempt to
     * re-create the ServerSocket.
     *
     * @param ex the exception that occurred during <code>ServerSocket</code>
     *           creation
     * @return if true, the RMI runtime attempts to retry
     * <code>ServerSocket</code> creation
     * @see java.rmi.server.RMISocketFactory#setFailureHandler(RMIFailureHandler)
     * @since JDK1.1
     */
    public boolean failure(Exception ex);

}

⏎ java/rmi/server/RMIFailureHandler.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)