org.pentaho.di.core.fileinput
Class CharsetToolkit

java.lang.Object
  org.pentaho.di.core.fileinput.CharsetToolkit

public class CharsetToolkit
extends 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);


 
Date: 18 juil. 2002




Author:
  
Guillaume LAFORGE








Constructor Summary
CharsetToolkit(byte[] buffer)



          Constructor of the com.glaforge.i18n.io.CharsetToolkit utility class.
CharsetToolkit(byte[] buffer,
               Charset defaultCharset)



          Constructor of the com.glaforge.i18n.io.CharsetToolkit utility class.
 



Method Summary




static Charset[]
getAvailableCharsets()



          Retrieves all the available Charsets on the platform,
 among which the default charset.



 Charset
getDefaultCharset()



          Retrieves the default Charset



static 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.



 Charset
guessEncoding()



          Guess the encoding of the provided buffer.



static Charset
guessEncoding(File f,
              int bufferLength)



           



static Charset
guessEncoding(File f,
              int bufferLength,
              Charset defaultCharset)



           



static Charset
guessEncoding(org.apache.commons.vfs.FileObject file,
              int bufferLength)



           



static String
guessEncodingName(File file)



           



static String
guessEncodingName(org.apache.commons.vfs.FileObject file)



           



 void
setDefaultCharset(Charset defaultCharset)



          Defines the default Charset used in case the buffer represents
 an 8-bit Charset.



 void
setEnforce8Bit(boolean enforce)



          If US-ASCII is recognized, enforce to return the default encoding, rather than US-ASCII.


 
Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 





Constructor Detail



CharsetToolkit
public CharsetToolkit(byte[] buffer)

Constructor of the com.glaforge.i18n.io.CharsetToolkit utility class.


Parameters:
buffer - the byte buffer of which we want to know the encoding.




CharsetToolkit
public CharsetToolkit(byte[] buffer,
                      Charset defaultCharset)

Constructor of the com.glaforge.i18n.io.CharsetToolkit utility class.


Parameters:
buffer - the byte buffer of which we want to know the encoding.
defaultCharset - the default Charset to use in case an 8-bit charset is recognized.





Method Detail



setDefaultCharset
public void setDefaultCharset(Charset defaultCharset)

Defines the default Charset used in case the buffer represents
 an 8-bit Charset.


Parameters:
defaultCharset - the default Charset to be returned by guessEncoding()
 if an 8-bit Charset is encountered.





guessEncoding
public static Charset guessEncoding(org.apache.commons.vfs.FileObject file,
                                    int bufferLength)
                             throws FileNotFoundException,
                                    IOException



Throws:
FileNotFoundException
IOException





guessEncodingName
public static String guessEncodingName(org.apache.commons.vfs.FileObject file)
                                throws FileNotFoundException,
                                       IOException



Throws:
FileNotFoundException
IOException





guessEncodingName
public static String guessEncodingName(File file)
                                throws FileNotFoundException,
                                       IOException



Throws:
FileNotFoundException
IOException





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 default charset rather than US-ASCII.


Parameters:
enforce - a boolean specifying the use or not of US-ASCII.





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.





getDefaultCharset
public Charset getDefaultCharset()

Retrieves the default Charset



Returns:






guessEncoding
public 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.





guessEncoding
public static Charset guessEncoding(File f,
                                    int bufferLength)
                             throws FileNotFoundException,
                                    IOException



Throws:
FileNotFoundException
IOException





guessEncoding
public static Charset guessEncoding(File f,
                                    int bufferLength,
                                    Charset defaultCharset)
                             throws FileNotFoundException,
                                    IOException



Throws:
FileNotFoundException
IOException





getDefaultSystemCharset
public static Charset getDefaultSystemCharset()

Retrieve the default charset of the system.



Returns:
the default Charset.





getAvailableCharsets
public static Charset[] getAvailableCharsets()

Retrieves all the available Charsets on the platform,
 among which the default charset.



Returns:
an array of Charsets.