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/imageio/spi/ImageTranscoderSpi.java

/*
 * Copyright (c) 2000, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package javax.imageio.spi;

import javax.imageio.ImageTranscoder;

/**
 * The service provider interface (SPI) for <code>ImageTranscoder</code>s.
 * For more information on service provider classes, see the class comment
 * for the <code>IIORegistry</code> class.
 *
 * @see IIORegistry
 * @see javax.imageio.ImageTranscoder
 *
 */
public abstract class ImageTranscoderSpi extends IIOServiceProvider {

    /**
     * Constructs a blank <code>ImageTranscoderSpi</code>.  It is up
     * to the subclass to initialize instance variables and/or
     * override method implementations in order to provide working
     * versions of all methods.
     */
    protected ImageTranscoderSpi() {
    }

    /**
     * Constructs an <code>ImageTranscoderSpi</code> with a given set
     * of values.
     *
     * @param vendorName the vendor name.
     * @param version a version identifier.
     */
    public ImageTranscoderSpi(String vendorName,
                              String version) {
        super(vendorName, version);
    }

    /**
     * Returns the fully qualified class name of an
     * <code>ImageReaderSpi</code> class that generates
     * <code>IIOMetadata</code> objects that may be used as input to
     * this transcoder.
     *
     * @return a <code>String</code> containing the fully-qualified
     * class name of the <code>ImageReaderSpi</code> implementation class.
     *
     * @see ImageReaderSpi
     */
    public abstract String getReaderServiceProviderName();

    /**
     * Returns the fully qualified class name of an
     * <code>ImageWriterSpi</code> class that generates
     * <code>IIOMetadata</code> objects that may be used as input to
     * this transcoder.
     *
     * @return a <code>String</code> containing the fully-qualified
     * class name of the <code>ImageWriterSpi</code> implementation class.
     *
     * @see ImageWriterSpi
     */
    public abstract String getWriterServiceProviderName();

    /**
     * Returns an instance of the <code>ImageTranscoder</code>
     * implementation associated with this service provider.
     *
     * @return an <code>ImageTranscoder</code> instance.
     */
    public abstract ImageTranscoder createTranscoderInstance();
}

⏎ javax/imageio/spi/ImageTranscoderSpi.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

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