"Java Modified UTF-8 Encoding" demek ne anlama geliyor?

"Java Modified UTF-8 Encoding" demek ne anlama geliyor? Normal UTF-8 Kodlamadan nasıl farklıdır?

7
Java, her zaman her şeyi yoluna koymak istiyor.
katma yazar BoltClock, kaynak
Bunu nerede söylüyor?
katma yazar millimoose, kaynak
@BoltClock Çok yapıcı bir yorum değil. Java'nın bu değiştirilmiş kodlamayı yalnızca, String'in 0x00 sonlandırılmış Dizeleri kullanan bir ortamda sonlanabileceği durumlarda kullandığı anlaşılıyor.
katma yazar Mark Rotteveel, kaynak

3 cevap

Bu, javados'unda ayrıntılı olarak açıklanmıştır. DataINput :

Modified UTF-8

Implementations of the DataInput and DataOutput interfaces represent Unicode strings in a format that is a slight modification of UTF-8. (For information regarding the standard UTF-8 format, see section 3.9 Unicode Encoding Forms of The Unicode Standard, Version 4.0). Note that in the following tables, the most significant bit appears in the far left-hand column.

... (some tables, please click the javadoc link to see yourself) ...

The differences between this format and the standard UTF-8 format are the following:

  • The null byte '\u0000' is encoded in 2-byte format rather than 1-byte, so that the encoded strings never have embedded nulls.
  • Only the 1-byte, 2-byte, and 3-byte formats are used.
  • Supplementary characters are represented in the form of surrogate pairs.

Bunu nasıl okuyacağınız, javadoc'ta ayrıntılı olarak açıklanmıştır. DataINput # readUTF() :

readUTF

String readUTF()
           throws IOException

Reads in a string that has been encoded using a modified UTF-8 format. The general contract of readUTF is that it reads a representation of a Unicode character string encoded in modified UTF-8 format; this string of characters is then returned as a String.

First, two bytes are read and used to construct an unsigned 16-bit integer in exactly the manner of the readUnsignedShort method . This integer value is called the UTF length and specifies the number of additional bytes to be read. These bytes are then converted to characters by considering them in groups. The length of each group is computed from the value of the first byte of the group. The byte following a group, if any, is the first byte of the next group.

If the first byte of a group matches the bit pattern 0xxxxxxx (where x means "may be 0 or 1"), then the group consists of just that byte. The byte is zero-extended to form a character.

If the first byte of a group matches the bit pattern 110xxxxx, then the group consists of that byte a and a second byte b. If there is no byte b (because byte a was the last of the bytes to be read), or if byte b does not match the bit pattern 10xxxxxx, then a UTFDataFormatException is thrown. Otherwise, the group is converted to the character:

(char)(((a& 0x1F) << 6) | (b & 0x3F))

If the first byte of a group matches the bit pattern 1110xxxx, then the group consists of that byte a and two more bytes b and c. If there is no byte c (because byte a was one of the last two of the bytes to be read), or either byte b or byte c does not match the bit pattern 10xxxxxx, then a UTFDataFormatException is thrown. Otherwise, the group is converted to the character:

(char)(((a & 0x0F) << 12) | ((b & 0x3F) << 6) | (c & 0x3F))

If the first byte of a group matches the pattern 1111xxxx or the pattern 10xxxxxx, then a UTFDataFormatException is thrown.

If end of file is encountered at any time during this entire process, then an EOFException is thrown.

After every group has been converted to a character by this process, the characters are gathered, in the same order in which their corresponding groups were read from the input stream, to form a String, which is returned.

The writeUTF method of interface DataOutput may be used to write data that is suitable for reading by this method.

8
katma
"Boş bayt 2 bayt biçiminde kodlanır" - Bu, 11000000 10000000 olarak kodlanmış olduğu anlamına mı geliyor?
katma yazar MC Emperor, kaynak

Dahili metin temsili için UTF-16 kullanan Java programlama dili, string serileştirme için standart olmayan UTF-8 modifikasyonunu destekler. Bu kodlamaya UTF-8 modifiye denir. Değiştirilmiş ve standart UTF-8 arasında iki fark vardır. İlk fark, boş karakterin (U + 0000), biri yerine 11000000 10000000 olmak üzere iki bayt ile kodlanmasıdır.

3
katma

Probably this: http://en.wikipedia.org/wiki/UTF-8#Modified_UTF-8

"Normal kullanımda, Java programlama dili standardı destekler   InputStreamReader üzerinden dizeleri okurken ve yazarken UTF-8 ve   OutputStreamWriter. Ancak nesne için Modifiye UTF-8 kullanır   Java Yerli Arabirimi için seri hale getirme ve   sınıf dosyalarına sabit dizeleri gömmek. "

1
katma