Java example source code file (FileTypeDetector.java)

This example Java source code file (FileTypeDetector.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

filetypedetector, ioexception, runtimepermission, securitymanager, string, void

The FileTypeDetector.java Java example source code

/*
 * Copyright (c) 2007, 2011, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

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 (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")
     */
    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,
     * 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">RFC 2045:
     * Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet
     * Message Bodies</i>. 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;
}