Java example source code file (MagicFileTypeDetector.java)

This example Java source code file (MagicFileTypeDetector.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

abstractfiletypedetector, ioexception, magicfiletypedetector, nativebuffer, override, privilegedaction, security, string, unixpath, unknow_mime_type, void

The MagicFileTypeDetector.java Java example source code

/*
 * Copyright (c) 2012, 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 sun.nio.fs;

import java.io.IOException;
import java.nio.file.Path;
import java.security.AccessController;
import java.security.PrivilegedAction;

/**
 * File type detector that uses the libmagic to guess the MIME type of a file.
 */

class MagicFileTypeDetector extends AbstractFileTypeDetector {

    private static final String UNKNOW_MIME_TYPE = "application/octet-stream";

    // true if libmagic is available and successfully loaded
    private final boolean libmagicAvailable;

    public MagicFileTypeDetector() {
        libmagicAvailable = initialize0();
    }

    @Override
    protected String implProbeContentType(Path obj) throws IOException {
        if (!libmagicAvailable || !(obj instanceof UnixPath))
            return null;

        UnixPath path = (UnixPath) obj;
        path.checkRead();

        NativeBuffer buffer = NativeBuffers.asNativeBuffer(path.getByteArrayForSysCalls());
        try {
            byte[] type = probe0(buffer.address());
            String mimeType = (type == null) ? null : new String(type);
            return UNKNOW_MIME_TYPE.equals(mimeType) ? null : mimeType;
        } finally {
            buffer.release();
        }
    }

    private static native boolean initialize0();

    private static native byte[] probe0(long pathAddress);

    static {
        AccessController.doPrivileged(new PrivilegedAction<Void>() {
            @Override
            public Void run() {
                System.loadLibrary("nio");
                return null;
            }
        });
    }
}