Package org.gephi.utils

Class CharsetToolkit

  • public class CharsetToolkit
extends Object
    Utility class to guess the encoding of a given text file.

    Unicode files encoded in UTF-16 (low or big endian) or UTF-8 files with a Byte Order Marker are correctly discovered. For UTF-8 files with no BOM, if the buffer is wide enough, the charset should also be discovered.

    A byte buffer of 4KB is usually sufficient to be able to guess the encoding.

    Usage: 

     // guess the encoding
 Charset guessedCharset = CharsetToolkit.guessEncoding(file, 4096);

 // create a reader with the correct charset
 CharsetToolkit toolkit = new CharsetToolkit(file);
 BufferedReader reader = toolkit.getReader();

 // read the file content
 String line;
 while ((line = br.readLine())!= null)
 {
     System.out.println(line);
 }
    Author:
    Guillaume Laforge

    • Field Detail

      • EMPTY_BYTE_ARRAY

        private static final byte[] EMPTY_BYTE_ARRAY

      • buffer

        private byte[] buffer

      • defaultCharset

        private Charset defaultCharset

      • enforce8Bit

        private boolean enforce8Bit

    • Constructor Detail

      • CharsetToolkit

        public CharsetToolkit​(InputStream stream)
               throws IOException
        Constructor of the CharsetToolkit utility class.
        Parameters:
        stream - of which we want to know the encoding.
        Throws:
        IOException - if an io error occurs

    • Method Detail

      • isContinuationChar

        private static boolean isContinuationChar​(byte b)
        If the byte has the form 10xxxxx, then it's a continuation byte of a multiple byte character;
        Parameters:
        b - a byte.
        Returns:
        true if it's a continuation char.

      • isTwoBytesSequence

        private static boolean isTwoBytesSequence​(byte b)
        If the byte has the form 110xxxx, then it's the first byte of a two-bytes sequence character.
        Parameters:
        b - a byte.
        Returns:
        true if it's the first byte of a two-bytes sequence.

      • isThreeBytesSequence

        private static boolean isThreeBytesSequence​(byte b)
        If the byte has the form 1110xxx, then it's the first byte of a three-bytes sequence character.
        Parameters:
        b - a byte.
        Returns:
        true if it's the first byte of a three-bytes sequence.

      • isFourBytesSequence

        private static boolean isFourBytesSequence​(byte b)
        If the byte has the form 11110xx, then it's the first byte of a four-bytes sequence character.
        Parameters:
        b - a byte.
        Returns:
        true if it's the first byte of a four-bytes sequence.

      • isFiveBytesSequence

        private static boolean isFiveBytesSequence​(byte b)
        If the byte has the form 11110xx, then it's the first byte of a five-bytes sequence character.
        Parameters:
        b - a byte.
        Returns:
        true if it's the first byte of a five-bytes sequence.

      • isSixBytesSequence

        private static boolean isSixBytesSequence​(byte b)
        If the byte has the form 1110xxx, then it's the first byte of a six-bytes sequence character.
        Parameters:
        b - a byte.
        Returns:
        true if it's the first byte of a six-bytes sequence.

      • 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.

      • getCharset

        public Charset getCharset()

      • 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.

      • 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.

      • getDefaultCharset

        public Charset getDefaultCharset()
        Retrieves the default Charset
        Returns:
        charset

      • 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

        private 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.

      • hasUTF8Bom

        public boolean hasUTF8Bom()
        Has a Byte Order Marker for UTF-8 (Used by Microsoft's Notepad and other editors).
        Returns:
        true if the buffer has a BOM for UTF8.

      • hasUTF16LEBom

        public boolean hasUTF16LEBom()
        Has a Byte Order Marker for UTF-16 Low Endian (ucs-2le, ucs-4le, and ucs-16le).
        Returns:
        true if the buffer has a BOM for UTF-16 Low Endian.

      • hasUTF16BEBom

        public boolean hasUTF16BEBom()
        Has a Byte Order Marker for UTF-16 Big Endian (utf-16 and ucs-2).
        Returns:
        true if the buffer has a BOM for UTF-16 Big Endian.

      • getReader

        public BufferedReader getReader()
        Gets a BufferedReader (indeed a LineNumberReader) from the File specified in the constructor of CharsetToolkit using the charset discovered by the method guessEncoding().
        Returns:
        a BufferedReader

      • hasXMLHeader

        private boolean hasXMLHeader()