Class CharsetToolkit
- java.lang.Object
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- outils.CharsetToolkit
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public class CharsetToolkit extends java.lang.Object
Utility class to guess the encoding of a given byte array. The guess is unfortunately not 100% sure. Especially for 8-bit charsets. It's not possible to know which 8-bit charset is used. Except through statistical analysis. We will then infer that the charset encountered is the same as the default standard charset.
On the other hand, unicode files encoded in UTF-16 (low or big endian) or UTF-8 files with a Byte Order Marker are easy to find. For UTF-8 files with no BOM, if the buffer is wide enough, it's easy to guess.
Tested against a complicated UTF-8 file, Sun's implementation does not render bad UTF-8 constructs as expected by the specification. But with a buffer wide enough, the method guessEncoding() did behave correctly and recognized the UTF-8 charset.
A byte buffer of 4KB or 8KB is sufficient to be able to guess the encoding.
Usage:
// guess the encoding Charset guessedCharset = com.glaforge.i18n.io.CharsetToolkit.guessEncoding(file, 4096); // create a reader with the charset we've just discovered FileInputStream fis = new FileInputStream(file); InputStreamReader isr = new InputStreamReader(fis, guessedCharset); BufferedReader br = new BufferedReader(isr); // read the file content String line; while ((line = br.readLine())!= null) { System.err.println(line); }
Date: 18 juil. 2002
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Constructor Summary
Constructors Constructor Description CharsetToolkit(byte[] buf)
Constructor of thecom.glaforge.i18n.io.CharsetToolkit
utility class.CharsetToolkit(byte[] buf, java.nio.charset.Charset defCharset)
Constructor of thecom.glaforge.i18n.io.CharsetToolkit
utility class.
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Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description static java.nio.charset.Charset[]
getAvailableCharsets()
Retrieves all the availableCharset
s on the platform, among which the defaultcharset
.java.nio.charset.Charset
getDefaultCharset()
Retrieves the default Charsetstatic java.nio.charset.Charset
getDefaultSystemCharset()
Retrieve the default charset of the system.boolean
getEnforce8Bit()
Gets the enforce8Bit flag, in case we do not want to ever get a US-ASCII encoding.java.nio.charset.Charset
guessEncoding()
Guess the encoding of the provided buffer.static java.nio.charset.Charset
guessEncoding(java.io.File f, int bufferLength)
essaie de deviner l'encodage du fichier fstatic java.nio.charset.Charset
guessEncoding(java.io.File f, int bufferLength, java.nio.charset.Charset defaultCharset)
essaie de deviner l'encodage du fichier fstatic void
main(java.lang.String[] args)
void
setDefaultCharset(java.nio.charset.Charset defCharset)
Defines the defaultCharset
used in case the buffer represents an 8-bitCharset
.void
setEnforce8Bit(boolean enforce)
If US-ASCII is recognized, enforce to return the default encoding, rather than US-ASCII.
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Constructor Detail
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CharsetToolkit
public CharsetToolkit(byte[] buf)
Constructor of thecom.glaforge.i18n.io.CharsetToolkit
utility class.- Parameters:
buf
- the byte buffer of which we want to know the encoding.
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CharsetToolkit
public CharsetToolkit(byte[] buf, java.nio.charset.Charset defCharset)
Constructor of thecom.glaforge.i18n.io.CharsetToolkit
utility class.- Parameters:
buf
- the byte buffer of which we want to know the encoding.defCharset
- the default Charset to use in case an 8-bit charset is recognized.
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Method Detail
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setDefaultCharset
public void setDefaultCharset(java.nio.charset.Charset defCharset)
Defines the defaultCharset
used in case the buffer represents an 8-bitCharset
.- Parameters:
defCharset
- the defaultCharset
to be returned byguessEncoding()
if an 8-bitCharset
is encountered.
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setEnforce8Bit
public void setEnforce8Bit(boolean enforce)
If US-ASCII is recognized, enforce to return the default encoding, rather than US-ASCII. It might be a file without any special character in the range 128-255, but that may be or become a file encoded with the defaultcharset
rather than US-ASCII.- Parameters:
enforce
- a boolean specifying the use or not of US-ASCII.
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getEnforce8Bit
public boolean getEnforce8Bit()
Gets the enforce8Bit flag, in case we do not want to ever get a US-ASCII encoding.- Returns:
- a boolean representing the flag of use of US-ASCII.
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getDefaultCharset
public java.nio.charset.Charset getDefaultCharset()
Retrieves the default Charset- Returns:
defaultCharset
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guessEncoding
public java.nio.charset.Charset guessEncoding()
Guess the encoding of the provided buffer.
If Byte Order Markers are encountered at the beginning of the buffer, we immidiately return the charset implied by this BOM. Otherwise, the file would not be a human readable text file.If there is no BOM, this method tries to discern whether the file is UTF-8 or not. If it is not UTF-8, we assume the encoding is the default system encoding (of course, it might be any 8-bit charset, but usually, an 8-bit charset is the default one).
It is possible to discern UTF-8 thanks to the pattern of characters with a multi-byte sequence.
UCS-4 range (hex.) UTF-8 octet sequence (binary) 0000 0000-0000 007F 0xxxxxxx 0000 0080-0000 07FF 110xxxxx 10xxxxxx 0000 0800-0000 FFFF 1110xxxx 10xxxxxx 10xxxxxx 0001 0000-001F FFFF 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx 0020 0000-03FF FFFF 111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 0400 0000-7FFF FFFF 1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
With UTF-8, 0xFE and 0xFF never appear.
- Returns:
- the Charset recognized.
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guessEncoding
public static java.nio.charset.Charset guessEncoding(java.io.File f, int bufferLength) throws java.io.FileNotFoundException, java.io.IOException
essaie de deviner l'encodage du fichier f- Parameters:
f
- le fichier dont on doit déterminer l'encodagebufferLength
- longueur du buffer- Returns:
- le charset détecté
- Throws:
java.io.FileNotFoundException
- fichier f non trouvéjava.io.IOException
- erreur de lecture du fichier f
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guessEncoding
public static java.nio.charset.Charset guessEncoding(java.io.File f, int bufferLength, java.nio.charset.Charset defaultCharset) throws java.io.FileNotFoundException, java.io.IOException
essaie de deviner l'encodage du fichier f- Parameters:
f
- le fichier dont on doit déterminer l'encodagebufferLength
- longueur du bufferdefaultCharset
- le charset par défaut à utiliser- Returns:
- le charset détecté
- Throws:
java.io.FileNotFoundException
- fichier f non trouvéjava.io.IOException
- erreur de lecture du fichier f
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getDefaultSystemCharset
public static java.nio.charset.Charset getDefaultSystemCharset()
Retrieve the default charset of the system.- Returns:
- the default
Charset
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getAvailableCharsets
public static java.nio.charset.Charset[] getAvailableCharsets()
Retrieves all the availableCharset
s on the platform, among which the defaultcharset
.- Returns:
- an array of
Charset
s.
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main
public static void main(java.lang.String[] args) throws java.io.FileNotFoundException, java.io.IOException
- Parameters:
args
- arguments de la fonction main- Throws:
java.io.FileNotFoundException
- fichier non trouvéjava.io.IOException
- erreur de lecture du fichier
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