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