Package org.apache.commons.io.filefilter

# Class MagicNumberFileFilter

java.lang.Object
org.apache.commons.io.filefilter.AbstractFileFilter
org.apache.commons.io.filefilter.MagicNumberFileFilter

All Implemented Interfaces:
  `FileFilter`, `FilenameFilter`, `Serializable`, `FileVisitor<Path>`, `PathMatcher`, `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 = FileUtils.current();
     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 = FileUtils.current();
     MagicNumberFileFilter tarFileFilter =
         MagicNumberFileFilter("ustar", 257);
     String[] tarFiles = dir.list(tarFileFilter);
     for (String tarFile : tarFiles) {
         System.out.println(tarFile);
     }

## Using NIO

     final Path dir = PathUtils.current();
     final AccumulatorPathVisitor visitor = AccumulatorPathVisitor.withLongCounters(MagicNumberFileFilter("ustar", 257));
     //
     // Walk one directory
     Files.walkFileTree(dir, Collections.emptySet(), 1, visitor);
     System.out.println(visitor.getPathCounters());
     System.out.println(visitor.getFileList());
     //
     visitor.getPathCounters().reset();
     //
     // Walk directory tree
     Files.walkFileTree(dir, visitor);
     System.out.println(visitor.getPathCounters());
     System.out.println(visitor.getDirList());
     System.out.println(visitor.getFileList());

## Deprecating Serialization

Serialization is deprecated and will be removed in 3.0.

## Deprecating Serialization

Serialization is deprecated and will be removed in 3.0.

Since:
  2.0
See Also:
  - `FileFilterUtils.magicNumberFileFilter(byte[])`
  - `FileFilterUtils.magicNumberFileFilter(String)`
  - `FileFilterUtils.magicNumberFileFilter(byte[], long)`
  - `FileFilterUtils.magicNumberFileFilter(String, long)`
  - Serialized Form

- ## Field Summary

  ### Fields inherited from interface org.apache.commons.io.filefilter.IOFileFilter

  `EMPTY_STRING_ARRAY`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `MagicNumberFileFilter(byte[] magicNumber)`
  Constructs a new MagicNumberFileFilter and associates it with the magic number to test for in files.
  `MagicNumberFileFilter(byte[] magicNumbers, 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(String magicNumber)`
  Constructs a new MagicNumberFileFilter and associates it with the magic number to test for in files.
  `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.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `boolean`
  `accept(File file)`
  Accepts the provided file if the file contains the file filter's magic number at the specified offset.
  `FileVisitResult`
  `accept(Path file, BasicFileAttributes attributes)`
  Accepts the provided file if the file contains the file filter's magic number at the specified offset.
  `String`
  `toString()`
  Returns a String representation of the file filter, which includes the magic number bytes and byte offset.

  ### Methods inherited from class org.apache.commons.io.filefilter.AbstractFileFilter

  `accept, handle, postVisitDirectory, preVisitDirectory, visitFile, visitFileFailed`

  ### Methods inherited from class java.lang.Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

  ### Methods inherited from interface org.apache.commons.io.filefilter.IOFileFilter

  `and, matches, negate, or`

- ## Constructor Details

  - ### 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[] magicNumbers, 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:
      `magicNumbers` - the magic number to look for in the file.
      `offset` - the byte offset in the file to start comparing bytes.
    Throws:
      `IllegalArgumentException` - if `magicNumber` 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);

    This method uses the virtual machine's `default charset`.

    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 the empty String, or `offset` is a negative number.

- ## Method Details

  - ### 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 `IOException`s 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 `IOException`s occur while reading the file, the file will be rejected.

    Specified by:
      `accept` in interface `IOFileFilter`
    Specified by:
      `accept` in interface `PathFilter`
    Parameters:
      `file` - the file to accept or reject.
      `attributes` - the path's basic attributes (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.