/*
* Copyright (C) 2010 ZXing authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.zxing.common;
import java.nio.charset.Charset;
import java.util.Map;
import com.google.zxing.DecodeHintType;
/**
* Common string-related functions.
*
* @author Sean Owen
* @author Alex Dupre
*/
public final class StringUtils {
private static final String PLATFORM_DEFAULT_ENCODING = Charset
.defaultCharset().name();
public static final String SHIFT_JIS = "SJIS";
public static final String GB2312 = "GB2312";
private static final String EUC_JP = "EUC_JP";
private static final String UTF8 = "UTF8";
private static final String ISO88591 = "ISO8859_1";
private static final boolean ASSUME_SHIFT_JIS = SHIFT_JIS
.equalsIgnoreCase(PLATFORM_DEFAULT_ENCODING)
|| EUC_JP.equalsIgnoreCase(PLATFORM_DEFAULT_ENCODING);
private StringUtils() {
}
/**
* @param bytes
* bytes encoding a string, whose encoding should be guessed
* @param hints
* decode hints if applicable
* @return name of guessed encoding; at the moment will only guess one of:
* {@link #SHIFT_JIS}, {@link #UTF8}, {@link #ISO88591}, or the
* platform default encoding if none of these can possibly be
* correct
*/
public static String guessEncoding(byte[] bytes,
Map<DecodeHintType, ?> hints) {
if (hints != null) {
String characterSet = (String) hints
.get(DecodeHintType.CHARACTER_SET);
if (characterSet != null) {
return characterSet;
}
}
// For now, merely tries to distinguish ISO-8859-1, UTF-8 and Shift_JIS,
// which should be by far the most common encodings.
int length = bytes.length;
boolean canBeISO88591 = true;
boolean canBeShiftJIS = true;
boolean canBeUTF8 = true;
int utf8BytesLeft = 0;
// int utf8LowChars = 0;
int utf2BytesChars = 0;
int utf3BytesChars = 0;
int utf4BytesChars = 0;
int sjisBytesLeft = 0;
// int sjisLowChars = 0;
int sjisKatakanaChars = 0;
// int sjisDoubleBytesChars = 0;
int sjisCurKatakanaWordLength = 0;
int sjisCurDoubleBytesWordLength = 0;
int sjisMaxKatakanaWordLength = 0;
int sjisMaxDoubleBytesWordLength = 0;
// int isoLowChars = 0;
// int isoHighChars = 0;
int isoHighOther = 0;
boolean utf8bom = bytes.length > 3 && bytes[0] == (byte) 0xEF
&& bytes[1] == (byte) 0xBB && bytes[2] == (byte) 0xBF;
for (int i = 0; i < length
&& (canBeISO88591 || canBeShiftJIS || canBeUTF8); i++) {
int value = bytes[i] & 0xFF;
// UTF-8 stuff
if (canBeUTF8) {
if (utf8BytesLeft > 0) {
if ((value & 0x80) == 0) {
canBeUTF8 = false;
} else {
utf8BytesLeft--;
}
} else if ((value & 0x80) != 0) {
if ((value & 0x40) == 0) {
canBeUTF8 = false;
} else {
utf8BytesLeft++;
if ((value & 0x20) == 0) {
utf2BytesChars++;
} else {
utf8BytesLeft++;
if ((value & 0x10) == 0) {
utf3BytesChars++;
} else {
utf8BytesLeft++;
if ((value & 0x08) == 0) {
utf4BytesChars++;
} else {
canBeUTF8 = false;
}
}
}
}
} // else {
// utf8LowChars++;
// }
}
// ISO-8859-1 stuff
if (canBeISO88591) {
if (value > 0x7F && value < 0xA0) {
canBeISO88591 = false;
} else if (value > 0x9F) {
if (value < 0xC0 || value == 0xD7 || value == 0xF7) {
isoHighOther++;
} // else {
// isoHighChars++;
// }
} // else {
// isoLowChars++;
// }
}
// Shift_JIS stuff
if (canBeShiftJIS) {
if (sjisBytesLeft > 0) {
if (value < 0x40 || value == 0x7F || value > 0xFC) {
canBeShiftJIS = false;
} else {
sjisBytesLeft--;
}
} else if (value == 0x80 || value == 0xA0 || value > 0xEF) {
canBeShiftJIS = false;
} else if (value > 0xA0 && value < 0xE0) {
sjisKatakanaChars++;
sjisCurDoubleBytesWordLength = 0;
sjisCurKatakanaWordLength++;
if (sjisCurKatakanaWordLength > sjisMaxKatakanaWordLength) {
sjisMaxKatakanaWordLength = sjisCurKatakanaWordLength;
}
} else if (value > 0x7F) {
sjisBytesLeft++;
// sjisDoubleBytesChars++;
sjisCurKatakanaWordLength = 0;
sjisCurDoubleBytesWordLength++;
if (sjisCurDoubleBytesWordLength > sjisMaxDoubleBytesWordLength) {
sjisMaxDoubleBytesWordLength = sjisCurDoubleBytesWordLength;
}
} else {
// sjisLowChars++;
sjisCurKatakanaWordLength = 0;
sjisCurDoubleBytesWordLength = 0;
}
}
}
if (canBeUTF8 && utf8BytesLeft > 0) {
canBeUTF8 = false;
}
if (canBeShiftJIS && sjisBytesLeft > 0) {
canBeShiftJIS = false;
}
// Easy -- if there is BOM or at least 1 valid not-single byte character
// (and no evidence it can't be UTF-8), done
if (canBeUTF8
&& (utf8bom || utf2BytesChars + utf3BytesChars + utf4BytesChars > 0)) {
return UTF8;
}
// Easy -- if assuming Shift_JIS or at least 3 valid consecutive
// not-ascii characters (and no evidence it can't be), done
if (canBeShiftJIS
&& (ASSUME_SHIFT_JIS || sjisMaxKatakanaWordLength >= 3 || sjisMaxDoubleBytesWordLength >= 3)) {
return SHIFT_JIS;
}
// Distinguishing Shift_JIS and ISO-8859-1 can be a little tough for
// short words. The crude heuristic is:
// - If we saw
// - only two consecutive katakana chars in the whole text, or
// - at least 10% of bytes that could be "upper" not-alphanumeric
// Latin1,
// - then we conclude Shift_JIS, else ISO-8859-1
if (canBeISO88591 && canBeShiftJIS) {
return (sjisMaxKatakanaWordLength == 2 && sjisKatakanaChars == 2)
|| isoHighOther * 10 >= length ? SHIFT_JIS : ISO88591;
}
// Otherwise, try in order ISO-8859-1, Shift JIS, UTF-8 and fall back to
// default platform encoding
if (canBeISO88591) {
return ISO88591;
}
if (canBeShiftJIS) {
return SHIFT_JIS;
}
if (canBeUTF8) {
return UTF8;
}
// Otherwise, we take a wild guess with platform encoding
return PLATFORM_DEFAULT_ENCODING;
}
}