org.apache.commons.io.filefilter

Class MagicNumberFileFilter

  • All Implemented Interfaces:
    FileFilter, FilenameFilter, Serializable, FileVisitor< Path>, PathFilter, PathVisitor, IOFileFilter

    public class MagicNumberFileFilter
    extends AbstractFileFilter
    implements Serializable

    File filter for matching files containing a "magic number". A magic number is a unique series of bytes common to all files of a specific file format. For instance, all Java class files begin with the bytes 0xCAFEBABE.

    Using Classic IO

     File dir = new File(".");
     MagicNumberFileFilter javaClassFileFilter =
         MagicNumberFileFilter(new byte[] {(byte) 0xCA, (byte) 0xFE,
           (byte) 0xBA, (byte) 0xBE});
     String[] javaClassFiles = dir.list(javaClassFileFilter);
     for (String javaClassFile : javaClassFiles) {
         System.out.println(javaClassFile);
     }
     

    Sometimes, such as in the case of TAR files, the magic number will be offset by a certain number of bytes in the file. In the case of TAR archive files, this offset is 257 bytes.

     File dir = new File(".");
     MagicNumberFileFilter tarFileFilter =
         MagicNumberFileFilter("ustar", 257);
     String[] tarFiles = dir.list(tarFileFilter);
     for (String tarFile : tarFiles) {
         System.out.println(tarFile);
     }
     

    Using NIO

     final Path dir = Paths.get("");
     final AccumulatorPathVisitor visitor = AccumulatorPathVisitor.withLongCounters(MagicNumberFileFilter("ustar", 257));
     //
     // Walk one dir
     Files.walkFileTree(dir, Collections.emptySet(), 1, visitor);
     System.out.println(visitor.getPathCounters());
     System.out.println(visitor.getFileList());
     //
     visitor.getPathCounters().reset();
     //
     // Walk dir tree
     Files.walkFileTree(dir, visitor);
     System.out.println(visitor.getPathCounters());
     System.out.println(visitor.getDirList());
     System.out.println(visitor.getFileList());
     
    Since:
    2.0
    See Also:
    FileFilterUtils.magicNumberFileFilter(byte[]), FileFilterUtils.magicNumberFileFilter(String), FileFilterUtils.magicNumberFileFilter(byte[], long), FileFilterUtils.magicNumberFileFilter(String, long), Serialized Form
    • Constructor Detail

      • MagicNumberFileFilter

        public MagicNumberFileFilter(byte[] magicNumber)

        Constructs a new MagicNumberFileFilter and associates it with the magic number to test for in files. This constructor assumes a starting offset of 0.

        It is important to note that the array is not cloned and that any changes to the magic number array after construction will affect the behavior of this file filter.

         MagicNumberFileFilter javaClassFileFilter =
             MagicNumberFileFilter(new byte[] {(byte) 0xCA, (byte) 0xFE,
               (byte) 0xBA, (byte) 0xBE});
         
        Parameters:
        magicNumber - the magic number to look for in the file.
        Throws:
        IllegalArgumentException - if magicNumber is null, or contains no bytes.
      • MagicNumberFileFilter

        public MagicNumberFileFilter(byte[] magicNumber,
                                     long offset)

        Constructs a new MagicNumberFileFilter and associates it with the magic number to test for in files and the byte offset location in the file to to look for that magic number.

         MagicNumberFileFilter tarFileFilter =
             MagicNumberFileFilter(new byte[] {0x75, 0x73, 0x74, 0x61, 0x72}, 257);
         
         MagicNumberFileFilter javaClassFileFilter =
             MagicNumberFileFilter(new byte[] {0xCA, 0xFE, 0xBA, 0xBE}, 0);
         
        Parameters:
        magicNumber - the magic number to look for in the file.
        offset - the byte offset in the file to start comparing bytes.
        Throws:
        IllegalArgumentException - if magicNumber is null, or contains no bytes, or offset is a negative number.
      • MagicNumberFileFilter

        public MagicNumberFileFilter(String magicNumber)

        Constructs a new MagicNumberFileFilter and associates it with the magic number to test for in files. This constructor assumes a starting offset of 0.

        Example usage:
         
         MagicNumberFileFilter xmlFileFilter =
             MagicNumberFileFilter("<?xml");
         
         
        Parameters:
        magicNumber - the magic number to look for in the file. The string is converted to bytes using the platform default charset.
        Throws:
        IllegalArgumentException - if magicNumber is null or the empty String.
      • MagicNumberFileFilter

        public MagicNumberFileFilter(String magicNumber,
                                     long offset)

        Constructs a new MagicNumberFileFilter and associates it with the magic number to test for in files and the byte offset location in the file to to look for that magic number.

         MagicNumberFileFilter tarFileFilter =
             MagicNumberFileFilter("ustar", 257);
         
        Parameters:
        magicNumber - the magic number to look for in the file. The string is converted to bytes using the platform default charset.
        offset - the byte offset in the file to start comparing bytes.
        Throws:
        IllegalArgumentException - if magicNumber is null or the empty String, or offset is a negative number.
    • Method Detail

      • accept

        public boolean accept(File file)

        Accepts the provided file if the file contains the file filter's magic number at the specified offset.

        If any IOExceptions occur while reading the file, the file will be rejected.

        Specified by:
        accept in interface  FileFilter
        Specified by:
        accept in interface  IOFileFilter
        Overrides:
        accept in class  AbstractFileFilter
        Parameters:
        file - the file to accept or reject.
        Returns:
        true if the file contains the filter's magic number at the specified offset, false otherwise.
      • accept

        public FileVisitResult accept(Path file,
                                      BasicFileAttributes attributes)

        Accepts the provided file if the file contains the file filter's magic number at the specified offset.

        If any IOExceptions occur while reading the file, the file will be rejected.

        Specified by:
        accept in interface  PathFilter
        Specified by:
        accept in interface  IOFileFilter
        Parameters:
        file - the file to accept or reject.
        attributes - the file's basic attributes (TODO may be null).
        Returns:
        true if the file contains the filter's magic number at the specified offset, false otherwise.
        Since:
        2.9.0
      • toString

        public String toString()
        Returns a String representation of the file filter, which includes the magic number bytes and byte offset.
        Overrides:
        toString in class  AbstractFileFilter
        Returns:
        a String representation of the file filter.

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