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/IIOServiceProvider.java

/*
 * Copyright (c) 2000, 2004, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package javax.imageio.spi;

import java.util.Locale;
import javax.imageio.spi.RegisterableService;
import javax.imageio.spi.ServiceRegistry;

/**
 * A superinterface for functionality common to all Image I/O service
 * provider interfaces (SPIs).  For more information on service
 * provider classes, see the class comment for the
 * <code>IIORegistry</code> class.
 *
 * @see IIORegistry
 * @see javax.imageio.spi.ImageReaderSpi
 * @see javax.imageio.spi.ImageWriterSpi
 * @see javax.imageio.spi.ImageTranscoderSpi
 * @see javax.imageio.spi.ImageInputStreamSpi
 *
 */
public abstract class IIOServiceProvider implements RegisterableService {

    /**
     * A <code>String</code> to be returned from
     * <code>getVendorName</code>, initially <code>null</code>.
     * Constructors should set this to a non-<code>null</code> value.
     */
    protected String vendorName;

    /**
     * A <code>String</code> to be returned from
     * <code>getVersion</code>, initially null.  Constructors should
     * set this to a non-<code>null</code> value.
     */
    protected String version;

    /**
     * Constructs an <code>IIOServiceProvider</code> with a given
     * vendor name and version identifier.
     *
     * @param vendorName the vendor name.
     * @param version a version identifier.
     *
     * @exception IllegalArgumentException if <code>vendorName</code>
     * is <code>null</code>.
     * @exception IllegalArgumentException if <code>version</code>
     * is <code>null</code>.
     */
    public IIOServiceProvider(String vendorName,
                              String version) {
        if (vendorName == null) {
            throw new IllegalArgumentException("vendorName == null!");
        }
        if (version == null) {
            throw new IllegalArgumentException("version == null!");
        }
        this.vendorName = vendorName;
        this.version = version;
    }

    /**
     * Constructs a blank <code>IIOServiceProvider</code>.  It is up
     * to the subclass to initialize instance variables and/or
     * override method implementations in order to ensure that the
     * <code>getVendorName</code> and <code>getVersion</code> methods
     * will return non-<code>null</code> values.
     */
    public IIOServiceProvider() {
    }

    /**
     * A callback that will be called exactly once after the Spi class
     * has been instantiated and registered in a
     * <code>ServiceRegistry</code>.  This may be used to verify that
     * the environment is suitable for this service, for example that
     * native libraries can be loaded.  If the service cannot function
     * in the environment where it finds itself, it should deregister
     * itself from the registry.
     *
     * <p> Only the registry should call this method.
     *
     * <p> The default implementation does nothing.
     *
     * @see ServiceRegistry#registerServiceProvider(Object provider)
     */
    public void onRegistration(ServiceRegistry registry,
                               Class<?> category) {}

    /**
     * A callback that will be whenever the Spi class has been
     * deregistered from a <code>ServiceRegistry</code>.
     *
     * <p> Only the registry should call this method.
     *
     * <p> The default implementation does nothing.
     *
     * @see ServiceRegistry#deregisterServiceProvider(Object provider)
     */
    public void onDeregistration(ServiceRegistry registry,
                                 Class<?> category) {}

    /**
     * Returns the name of the vendor responsible for creating this
     * service provider and its associated implementation.  Because
     * the vendor name may be used to select a service provider,
     * it is not localized.
     *
     * <p> The default implementation returns the value of the
     * <code>vendorName</code> instance variable.
     *
     * @return a non-<code>null</code> <code>String</code> containing
     * the name of the vendor.
     */
    public String getVendorName() {
        return vendorName;
    }

    /**
     * Returns a string describing the version
     * number of this service provider and its associated
     * implementation.  Because the version may be used by transcoders
     * to identify the service providers they understand, this method
     * is not localized.
     *
     * <p> The default implementation returns the value of the
     * <code>version</code> instance variable.
     *
     * @return a non-<code>null</code> <code>String</code> containing
     * the version of this service provider.
     */
    public String getVersion() {
        return version;
    }

    /**
     * Returns a brief, human-readable description of this service
     * provider and its associated implementation.  The resulting
     * string should be localized for the supplied
     * <code>Locale</code>, if possible.
     *
     * @param locale a <code>Locale</code> for which the return value
     * should be localized.
     *
     * @return a <code>String</code> containing a description of this
     * service provider.
     */
    public abstract String getDescription(Locale locale);
}

⏎ javax/imageio/spi/IIOServiceProvider.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)