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java.lang.Object org.apache.commons.io.filefilter.AbstractFileFilter org.apache.commons.io.filefilter.MagicNumberFileFilter
public class MagicNumberFileFilter
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);
}
FileFilterUtils.magicNumberFileFilter(byte[])
,
FileFilterUtils.magicNumberFileFilter(String)
,
FileFilterUtils.magicNumberFileFilter(byte[], long)
,
FileFilterUtils.magicNumberFileFilter(String, long)
,
Serialized FormConstructor Summary | |
---|---|
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 | |
---|---|
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 |
---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Constructor Detail |
---|
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});
magicNumber
- the magic number to look for in the file.
IllegalArgumentException
- if magicNumber
is
null
, or contains no bytes.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
.
MagicNumberFileFilter xmlFileFilter =
MagicNumberFileFilter("<?xml");
magicNumber
- the magic number to look for in the file.
The string is converted to bytes using the platform default charset.
IllegalArgumentException
- if magicNumber
is
null
or the empty String.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);
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.
IllegalArgumentException
- if magicNumber
is
null
or the empty String, or offset
is
a negative number.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.
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 tarFileFilter =
MagicNumberFileFilter(new byte[] {0x75, 0x73, 0x74, 0x61, 0x72}, 257);
MagicNumberFileFilter javaClassFileFilter =
MagicNumberFileFilter(new byte[] {0xCA, 0xFE, 0xBA, 0xBE}, 0);
magicNumber
- the magic number to look for in the file.offset
- the byte offset in the file to start comparing bytes.
IllegalArgumentException
- if magicNumber
is
null
, or contains no bytes, or offset
is a negative number.Method Detail |
---|
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.
accept
in interface FileFilter
accept
in interface IOFileFilter
accept
in class AbstractFileFilter
file
- the file to accept or reject.
true
if the file contains the filter's magic number
at the specified offset, false
otherwise.public String toString()
toString
in class AbstractFileFilter
|
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