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13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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25 
26 package java.nio.file.spi;
27 
28 import java.nio.file.Path;
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(Path)
46  *
47  * @since 1.7
48  */
49 
50 public abstract class FileTypeDetector {
51 
checkPermission()52     private static Void checkPermission() {
53         SecurityManager sm = System.getSecurityManager();
54         if (sm != null)
55             sm.checkPermission(new RuntimePermission("fileTypeDetector"));
56         return null;
57     }
FileTypeDetector(Void ignore)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      */
FileTypeDetector()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   path
87      *          the path to 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      */
probeContentType(Path path)104     public abstract String probeContentType(Path path)
105         throws IOException;
106 }
107