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, 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.

 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);
 }
 

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[] 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(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.
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

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

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(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.

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.

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.

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.