001    /*
002     * $Id: CharsetToolkit.java,v 1.2 2004/07/11 19:41:25 glaforge Exp $
003     *
004     * Copyright 2003 (C) Guillaume Laforge. All Rights Reserved.
005     *
006     * Redistribution and use of this software and associated documentation
007     * ("Software"), with or without modification, are permitted provided that the
008     * following conditions are met:
009     *  1. Redistributions of source code must retain copyright statements and
010     * notices. Redistributions must also contain a copy of this document.
011     *  2. Redistributions in binary form must reproduce the above copyright
012     * notice, this list of conditions and the following disclaimer in the
013     * documentation and/or other materials provided with the distribution.
014     *  3. The name "groovy" must not be used to endorse or promote products
015     * derived from this Software without prior written permission of The Codehaus.
016     * For written permission, please contact info@codehaus.org.
017     *  4. Products derived from this Software may not be called "groovy" nor may
018     * "groovy" appear in their names without prior written permission of The
019     * Codehaus. "groovy" is a registered trademark of The Codehaus.
020     *  5. Due credit should be given to The Codehaus - http://groovy.codehaus.org/
021     *
022     * THIS SOFTWARE IS PROVIDED BY THE CODEHAUS AND CONTRIBUTORS ``AS IS'' AND ANY
023     * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
024     * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
025     * DISCLAIMED. IN NO EVENT SHALL THE CODEHAUS OR ITS CONTRIBUTORS BE LIABLE FOR
026     * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
027     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
028     * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
029     * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
030     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
031     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
032     * DAMAGE.
033     *
034     */
035    
036    package groovy.util;
037    
038    import java.io.*;
039    import java.nio.charset.Charset;
040    import java.util.*;
041    
042    /**
043     * <p>Utility class to guess the encoding of a given text file.</p>
044     *
045     * <p>Unicode files encoded in UTF-16 (low or big endian) or UTF-8 files
046     * with a Byte Order Marker are correctly discovered. For UTF-8 files with no BOM, if the buffer
047     * is wide enough, the charset should also be discovered.</p>
048     *
049     * <p>A byte buffer of 4KB is usually sufficient to be able to guess the encoding.</p>
050     *
051     * <p>Usage:</p>
052     * <pre>
053     * // guess the encoding
054     * Charset guessedCharset = CharsetToolkit.guessEncoding(file, 4096);
055     *
056     * // create a reader with the correct charset
057     * CharsetToolkit toolkit = new CharsetToolkit(file);
058     * BufferedReader reader = toolkit.getReader();
059     *
060     * // read the file content
061     * String line;
062     * while ((line = br.readLine())!= null)
063     * {
064     *     System.out.println(line);
065     * }
066     * </pre>
067     *
068     * @author Guillaume Laforge
069     */
070    public class CharsetToolkit {
071        private byte[] buffer;
072        private Charset defaultCharset;
073        private Charset charset;
074        private boolean enforce8Bit = true;
075        private File file;
076    
077        /**
078         * Constructor of the <code>CharsetToolkit</code> utility class.
079         *
080         * @param file of which we want to know the encoding.
081         */
082        public CharsetToolkit(File file) throws IOException {
083            this.file = file;
084            InputStream input = new FileInputStream(file);
085            byte[] bytes = new byte[4096];
086            int bytesRead = input.read(bytes);
087            if (bytesRead == -1) {
088                this.buffer = new byte[0];
089            }
090            else if (bytesRead < 4096) {
091                byte[] bytesToGuess = new byte[bytesRead];
092                System.arraycopy(bytes, 0, bytesToGuess, 0, bytesRead);
093                this.buffer = bytesToGuess;
094            }
095            else {
096                this.buffer = bytes;
097            }
098            this.defaultCharset = getDefaultSystemCharset();
099            this.charset = null;
100        }
101    
102        /**
103         * Defines the default <code>Charset</code> used in case the buffer represents
104         * an 8-bit <code>Charset</code>.
105         *
106         * @param defaultCharset the default <code>Charset</code> to be returned by <code>guessEncoding()</code>
107         * if an 8-bit <code>Charset</code> is encountered.
108         */
109        public void setDefaultCharset(Charset defaultCharset) {
110            if (defaultCharset != null)
111                this.defaultCharset = defaultCharset;
112            else
113                this.defaultCharset = getDefaultSystemCharset();
114        }
115    
116        public Charset getCharset() {
117            if (this.charset == null)
118                this.charset = guessEncoding();
119            return charset;
120        }
121    
122        /**
123         * If US-ASCII is recognized, enforce to return the default encoding, rather than US-ASCII.
124         * It might be a file without any special character in the range 128-255, but that may be or become
125         * a file encoded with the default <code>charset</code> rather than US-ASCII.
126         *
127         * @param enforce a boolean specifying the use or not of US-ASCII.
128         */
129        public void setEnforce8Bit(boolean enforce) {
130            this.enforce8Bit = enforce;
131        }
132    
133        /**
134         * Gets the enforce8Bit flag, in case we do not want to ever get a US-ASCII encoding.
135         *
136         * @return a boolean representing the flag of use of US-ASCII.
137         */
138        public boolean getEnforce8Bit() {
139            return this.enforce8Bit;
140        }
141    
142        /**
143         * Retrieves the default Charset
144         * @return
145         */
146        public Charset getDefaultCharset() {
147            return defaultCharset;
148        }
149    
150        /**
151         * <p>Guess the encoding of the provided buffer.</p>
152         * If Byte Order Markers are encountered at the beginning of the buffer, we immidiately
153         * return the charset implied by this BOM. Otherwise, the file would not be a human
154         * readable text file.</p>
155         *
156         * <p>If there is no BOM, this method tries to discern whether the file is UTF-8 or not.
157         * If it is not UTF-8, we assume the encoding is the default system encoding
158         * (of course, it might be any 8-bit charset, but usually, an 8-bit charset is the default one).</p>
159         *
160         * <p>It is possible to discern UTF-8 thanks to the pattern of characters with a multi-byte sequence.</p>
161         * <pre>
162         * UCS-4 range (hex.)        UTF-8 octet sequence (binary)
163         * 0000 0000-0000 007F       0xxxxxxx
164         * 0000 0080-0000 07FF       110xxxxx 10xxxxxx
165         * 0000 0800-0000 FFFF       1110xxxx 10xxxxxx 10xxxxxx
166         * 0001 0000-001F FFFF       11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
167         * 0020 0000-03FF FFFF       111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
168         * 0400 0000-7FFF FFFF       1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
169         * </pre>
170         * <p>With UTF-8, 0xFE and 0xFF never appear.</p>
171         *
172         * @return the Charset recognized.
173         */
174        private Charset guessEncoding() {
175            // if the file has a Byte Order Marker, we can assume the file is in UTF-xx
176            // otherwise, the file would not be human readable
177            if (hasUTF8Bom())
178                return Charset.forName("UTF-8");
179            if (hasUTF16LEBom())
180                return Charset.forName("UTF-16LE");
181            if (hasUTF16BEBom())
182                return Charset.forName("UTF-16BE");
183    
184            // if a byte has its most significant bit set, the file is in UTF-8 or in the default encoding
185            // otherwise, the file is in US-ASCII
186            boolean highOrderBit = false;
187    
188            // if the file is in UTF-8, high order bytes must have a certain value, in order to be valid
189            // if it's not the case, we can assume the encoding is the default encoding of the system
190            boolean validU8Char = true;
191    
192            // TODO the buffer is not read up to the end, but up to length - 6
193    
194            int length = buffer.length;
195            int i = 0;
196            while (i < length - 6) {
197                byte b0 = buffer[i];
198                byte b1 = buffer[i + 1];
199                byte b2 = buffer[i + 2];
200                byte b3 = buffer[i + 3];
201                byte b4 = buffer[i + 4];
202                byte b5 = buffer[i + 5];
203                if (b0 < 0) {
204                    // a high order bit was encountered, thus the encoding is not US-ASCII
205                    // it may be either an 8-bit encoding or UTF-8
206                    highOrderBit = true;
207                    // a two-bytes sequence was encoutered
208                    if (isTwoBytesSequence(b0)) {
209                        // there must be one continuation byte of the form 10xxxxxx,
210                        // otherwise the following characteris is not a valid UTF-8 construct
211                        if (!isContinuationChar(b1))
212                            validU8Char = false;
213                        else
214                            i++;
215                    }
216                    // a three-bytes sequence was encoutered
217                    else if (isThreeBytesSequence(b0)) {
218                        // there must be two continuation bytes of the form 10xxxxxx,
219                        // otherwise the following characteris is not a valid UTF-8 construct
220                        if (!(isContinuationChar(b1) && isContinuationChar(b2)))
221                            validU8Char = false;
222                        else
223                            i += 2;
224                    }
225                    // a four-bytes sequence was encoutered
226                    else if (isFourBytesSequence(b0)) {
227                        // there must be three continuation bytes of the form 10xxxxxx,
228                        // otherwise the following characteris is not a valid UTF-8 construct
229                        if (!(isContinuationChar(b1) && isContinuationChar(b2) && isContinuationChar(b3)))
230                            validU8Char = false;
231                        else
232                            i += 3;
233                    }
234                    // a five-bytes sequence was encoutered
235                    else if (isFiveBytesSequence(b0)) {
236                        // there must be four continuation bytes of the form 10xxxxxx,
237                        // otherwise the following characteris is not a valid UTF-8 construct
238                        if (!(isContinuationChar(b1)
239                            && isContinuationChar(b2)
240                            && isContinuationChar(b3)
241                            && isContinuationChar(b4)))
242                            validU8Char = false;
243                        else
244                            i += 4;
245                    }
246                    // a six-bytes sequence was encoutered
247                    else if (isSixBytesSequence(b0)) {
248                        // there must be five continuation bytes of the form 10xxxxxx,
249                        // otherwise the following characteris is not a valid UTF-8 construct
250                        if (!(isContinuationChar(b1)
251                            && isContinuationChar(b2)
252                            && isContinuationChar(b3)
253                            && isContinuationChar(b4)
254                            && isContinuationChar(b5)))
255                            validU8Char = false;
256                        else
257                            i += 5;
258                    }
259                    else
260                        validU8Char = false;
261                }
262                if (!validU8Char)
263                    break;
264                i++;
265            }
266            // if no byte with an high order bit set, the encoding is US-ASCII
267            // (it might have been UTF-7, but this encoding is usually internally used only by mail systems)
268            if (!highOrderBit) {
269                // returns the default charset rather than US-ASCII if the enforce8Bit flag is set.
270                if (this.enforce8Bit)
271                    return this.defaultCharset;
272                else
273                    return Charset.forName("US-ASCII");
274            }
275            // if no invalid UTF-8 were encountered, we can assume the encoding is UTF-8,
276            // otherwise the file would not be human readable
277            if (validU8Char)
278                return Charset.forName("UTF-8");
279            // finally, if it's not UTF-8 nor US-ASCII, let's assume the encoding is the default encoding
280            return this.defaultCharset;
281        }
282    
283        /**
284         * If the byte has the form 10xxxxx, then it's a continuation byte of a multiple byte character;
285         *
286         * @param b a byte.
287         * @return true if it's a continuation char.
288         */
289        private static boolean isContinuationChar(byte b) {
290            return -128 <= b && b <= -65;
291        }
292    
293        /**
294         * If the byte has the form 110xxxx, then it's the first byte of a two-bytes sequence character.
295         *
296         * @param b a byte.
297         * @return true if it's the first byte of a two-bytes sequence.
298         */
299        private static boolean isTwoBytesSequence(byte b) {
300            return -64 <= b && b <= -33;
301        }
302    
303        /**
304         * If the byte has the form 1110xxx, then it's the first byte of a three-bytes sequence character.
305         *
306         * @param b a byte.
307         * @return true if it's the first byte of a three-bytes sequence.
308         */
309        private static boolean isThreeBytesSequence(byte b) {
310            return -32 <= b && b <= -17;
311        }
312    
313        /**
314         * If the byte has the form 11110xx, then it's the first byte of a four-bytes sequence character.
315         *
316         * @param b a byte.
317         * @return true if it's the first byte of a four-bytes sequence.
318         */
319        private static boolean isFourBytesSequence(byte b) {
320            return -16 <= b && b <= -9;
321        }
322    
323        /**
324         * If the byte has the form 11110xx, then it's the first byte of a five-bytes sequence character.
325         *
326         * @param b a byte.
327         * @return true if it's the first byte of a five-bytes sequence.
328         */
329        private static boolean isFiveBytesSequence(byte b) {
330            return -8 <= b && b <= -5;
331        }
332    
333        /**
334         * If the byte has the form 1110xxx, then it's the first byte of a six-bytes sequence character.
335         *
336         * @param b a byte.
337         * @return true if it's the first byte of a six-bytes sequence.
338         */
339        private static boolean isSixBytesSequence(byte b) {
340            return -4 <= b && b <= -3;
341        }
342    
343        /**
344         * Retrieve the default charset of the system.
345         *
346         * @return the default <code>Charset</code>.
347         */
348        public static Charset getDefaultSystemCharset() {
349            return Charset.forName(System.getProperty("file.encoding"));
350        }
351    
352        /**
353         * Has a Byte Order Marker for UTF-8 (Used by Microsoft's Notepad and other editors).
354         *
355         * @return true if the buffer has a BOM for UTF8.
356         */
357        public boolean hasUTF8Bom() {
358            if (buffer.length >= 3)
359                return (buffer[0] == -17 && buffer[1] == -69 && buffer[2] == -65);
360            else
361                return false;
362        }
363    
364        /**
365         * Has a Byte Order Marker for UTF-16 Low Endian
366         * (ucs-2le, ucs-4le, and ucs-16le).
367         *
368         * @return true if the buffer has a BOM for UTF-16 Low Endian.
369         */
370        public boolean hasUTF16LEBom() {
371            if (buffer.length >= 2)
372                return (buffer[0] == -1 && buffer[1] == -2);
373            else
374                return false;
375        }
376    
377        /**
378         * Has a Byte Order Marker for UTF-16 Big Endian
379         * (utf-16 and ucs-2).
380         *
381         * @return true if the buffer has a BOM for UTF-16 Big Endian.
382         */
383        public boolean hasUTF16BEBom() {
384            if (buffer.length >= 2)
385                return (buffer[0] == -2 && buffer[1] == -1);
386            else
387                return false;
388        }
389    
390        /**
391         * Gets a <code>BufferedReader</code> (indeed a <code>LineNumberReader</code>) from the <code>File</code>
392         * specified in the constructor of <code>CharsetToolkit</code> using the charset discovered by the
393         * method <code>guessEncoding()</code>.
394         *
395         * @return a <code>BufferedReader</code>
396         * @throws FileNotFoundException if the file is not found.
397         */
398        public BufferedReader getReader() throws FileNotFoundException {
399            LineNumberReader reader = new LineNumberReader(new InputStreamReader(new FileInputStream(file), getCharset()));
400            if (hasUTF8Bom() || hasUTF16LEBom() || hasUTF16BEBom()) {
401                try {
402                    reader.read();
403                }
404                catch (IOException e) {
405                    // should never happen, as a file with no content
406                    // but with a BOM has at least one char
407                }
408            }
409            return reader;
410        }
411    
412        /**
413         * Retrieves all the available <code>Charset</code>s on the platform,
414         * among which the default <code>charset</code>.
415         *
416         * @return an array of <code>Charset</code>s.
417         */
418        public static Charset[] getAvailableCharsets() {
419            Collection collection = Charset.availableCharsets().values();
420            return (Charset[]) collection.toArray(new Charset[collection.size()]);
421        }
422    }