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/management/remote/MBeanServerForwarder.java

/*
 * Copyright (c) 2003, 2007, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package javax.management.remote;

import javax.management.MBeanServer;

/**
 * <p>An object of this class implements the MBeanServer interface and
 * wraps another object that also implements that interface.
 * Typically, an implementation of this interface performs some action
 * in some or all methods of the <code>MBeanServer</code> interface
 * before and/or after forwarding the method to the wrapped object.
 * Examples include security checking and logging.</p>
 *
 * @since 1.5
 */
public interface MBeanServerForwarder extends MBeanServer {

    /**
     * Returns the MBeanServer object to which requests will be forwarded.
     *
     * @return the MBeanServer object to which requests will be forwarded,
     * or null if there is none.
     *
     * @see #setMBeanServer
     */
    public MBeanServer getMBeanServer();

    /**
     * Sets the MBeanServer object to which requests will be forwarded
     * after treatment by this object.
     *
     * @param mbs the MBeanServer object to which requests will be forwarded.
     *
     * @exception IllegalArgumentException if this object is already
     * forwarding to an MBeanServer object or if <code>mbs</code> is
     * null or if <code>mbs</code> is identical to this object.
     *
     * @see #getMBeanServer
     */
    public void setMBeanServer(MBeanServer mbs);
}

⏎ javax/management/remote/MBeanServerForwarder.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)