1 /*

     2  * Copyright 2007-2009 Sun Microsystems, Inc.  All Rights Reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.  Sun designates this

     8  * particular file as subject to the "Classpath" exception as provided

     9  * by Sun in the LICENSE file that accompanied this code.

    10  *

    11  * This code is distributed in the hope that it will be useful, but WITHOUT

    12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    14  * version 2 for more details (a copy is included in the LICENSE file that

    15  * accompanied this code).

    16  *

    17  * You should have received a copy of the GNU General Public License version

    18  * 2 along with this work; if not, write to the Free Software Foundation,

    19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    20  *

    21  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

    22  * CA 95054 USA or visit www.sun.com if you need additional information or

    23  * have any questions.

    24  */

    25 

    26 package java.nio.file.spi;

    27 

    28 import java.nio.file.FileRef;

    29 import java.io.IOException;

    30 

    31 /**

    32  * A file type detector for probing a file to guess its file type.

    33  *

    34  * <p> A file type detector is a concrete implementation of this class, has a

    35  * zero-argument constructor, and implements the abstract methods specified

    36  * below.

    37  *

    38  * <p> The means by which a file type detector determines the file type is

    39  * highly implementation specific. A simple implementation might examine the

    40  * <em>file extension</em> (a convention used in some platforms) and map it to

    41  * a file type. In other cases, the file type may be stored as a file <a

    42  * href="../attribute/package-summary.html"> attribute</a> or the bytes in a

    43  * file may be examined to guess its file type.

    44  *

    45  * @see java.nio.file.Files#probeContentType(FileRef)

    46  *

    47  * @since 1.7

    48  */

    49 

    50 public abstract class FileTypeDetector {

    51 

    52     private static Void checkPermission() {

    53         SecurityManager sm = System.getSecurityManager();

    54         if (sm != null)

    55             sm.checkPermission(new RuntimePermission("fileTypeDetector"));

    56         return null;

    57     }

    58     private FileTypeDetector(Void ignore) { }

    59 

    60     /**

    61      * Initializes a new instance of this class.

    62      *

    63      * @throws  SecurityException

    64      *          If a security manager has been installed and it denies

    65      *          {@link RuntimePermission}<tt>("fileTypeDetector")</tt>

    66      */

    67     protected FileTypeDetector() {

    68         this(checkPermission());

    69     }

    70 

    71     /**

    72      * Probes the given file to guess its content type.

    73      *

    74      * <p> The means by which this method determines the file type is highly

    75      * implementation specific. It may simply examine the file name, it may use

    76      * a file <a href="../attribute/package-summary.html">attribute</a>,

    77      * or it may examines bytes in the file.

    78      *

    79      * <p> The probe result is the string form of the value of a

    80      * Multipurpose Internet Mail Extension (MIME) content type as

    81      * defined by <a href="http://www.ietf.org/rfc/rfc2045.txt"><i>RFC&nbsp;2045:

    82      * Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet

    83      * Message Bodies</i></a>. The string must be parsable according to the

    84      * grammar in the RFC 2045.

    85      *

    86      * @param   file

    87      *          The file to probe

    88      *

    89      * @return  The content type or {@code null} if the file type is not

    90      *          recognized

    91      *

    92      * @throws  IOException

    93      *          An I/O error occurs

    94      * @throws  SecurityException

    95      *          If the implementation requires to access the file, and a

    96      *          security manager is installed, and it denies an unspecified

    97      *          permission required by a file system provider implementation.

    98      *          If the file reference is associated with the default file system

    99      *          provider then the {@link SecurityManager#checkRead(String)} method

   100      *          is invoked to check read access to the file.

   101      *

   102      * @see java.nio.file.Files#probeContentType

   103      */

   104     public abstract String probeContentType(FileRef file)

   105         throws IOException;

   106 }