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/nio/file/spi/FileTypeDetector.java

/*
 * Copyright (c) 2007, 2011, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package java.nio.file.spi;

import java.nio.file.Path;
import java.io.IOException;

/**
 * A file type detector for probing a file to guess its file type.
 *
 * <p> A file type detector is a concrete implementation of this class, has a
 * zero-argument constructor, and implements the abstract methods specified
 * below.
 *
 * <p> The means by which a file type detector determines the file type is
 * highly implementation specific. A simple implementation might examine the
 * <em>file extension</em> (a convention used in some platforms) and map it to
 * a file type. In other cases, the file type may be stored as a file <a
 * href="../attribute/package-summary.html"> attribute</a> or the bytes in a
 * file may be examined to guess its file type.
 *
 * @see java.nio.file.Files#probeContentType(Path)
 *
 * @since 1.7
 */

public abstract class FileTypeDetector {

    private static Void checkPermission() {
        SecurityManager sm = System.getSecurityManager();
        if (sm != null)
            sm.checkPermission(new RuntimePermission("fileTypeDetector"));
        return null;
    }
    private FileTypeDetector(Void ignore) { }

    /**
     * Initializes a new instance of this class.
     *
     * @throws  SecurityException
     *          If a security manager has been installed and it denies
     *          {@link RuntimePermission}<tt>("fileTypeDetector")</tt>
     */
    protected FileTypeDetector() {
        this(checkPermission());
    }

    /**
     * Probes the given file to guess its content type.
     *
     * <p> The means by which this method determines the file type is highly
     * implementation specific. It may simply examine the file name, it may use
     * a file <a href="../attribute/package-summary.html">attribute</a>,
     * or it may examines bytes in the file.
     *
     * <p> The probe result is the string form of the value of a
     * Multipurpose Internet Mail Extension (MIME) content type as
     * defined by <a href="http://www.ietf.org/rfc/rfc2045.txt"><i>RFC&nbsp;2045:
     * Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet
     * Message Bodies</i></a>. The string must be parsable according to the
     * grammar in the RFC 2045.
     *
     * @param   path
     *          the path to the file to probe
     *
     * @return  The content type or {@code null} if the file type is not
     *          recognized
     *
     * @throws  IOException
     *          An I/O error occurs
     * @throws  SecurityException
     *          If the implementation requires to access the file, and a
     *          security manager is installed, and it denies an unspecified
     *          permission required by a file system provider implementation.
     *          If the file reference is associated with the default file system
     *          provider then the {@link SecurityManager#checkRead(String)} method
     *          is invoked to check read access to the file.
     *
     * @see java.nio.file.Files#probeContentType
     */
    public abstract String probeContentType(Path path)
        throws IOException;
}

⏎ java/nio/file/spi/FileTypeDetector.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 

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