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Groovy: A powerful, dynamic language for the JVM
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 groovy.util;
import java.io.*;
import java.nio.charset.Charset;
import java.util.Collection;
/**
* 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 used to be able to guess the encoding.
*
* Usage:
*
* CharsetToolkit toolkit = new CharsetToolkit(file);
*
* // guess the encoding
* Charset guessedCharset = toolkit.getCharset();
*
* // create a reader with the correct charset
* BufferedReader reader = toolkit.getReader();
*
* // read the file content
* String line;
* while ((line = br.readLine())!= null)
* {
* System.out.println(line);
* }
*
*
* @author Guillaume Laforge
*/
public class CharsetToolkit {
private byte[] buffer;
private Charset defaultCharset;
private Charset charset;
private boolean enforce8Bit = true;
private final File file;
private static final byte[] EMPTY_BYTE_ARRAY = new byte[0];
/**
* Constructor of the CharsetToolkit utility class.
*
* @param file of which we want to know the encoding.
*/
public CharsetToolkit(File file) throws IOException {
this.file = file;
this.defaultCharset = getDefaultSystemCharset();
this.charset = null;
InputStream input = new FileInputStream(file);
try {
byte[] bytes = new byte[4096];
int bytesRead = input.read(bytes);
if (bytesRead == -1) {
this.buffer = EMPTY_BYTE_ARRAY;
}
else if (bytesRead < 4096) {
byte[] bytesToGuess = new byte[bytesRead];
System.arraycopy(bytes, 0, bytesToGuess, 0, bytesRead);
this.buffer = bytesToGuess;
}
else {
this.buffer = bytes;
}
} finally {
try {input.close();} catch (IOException e){
// IGNORE
}
}
}
/**
* Defines the default Charset used in case the buffer represents
* an 8-bit Charset.
*
* @param defaultCharset the default Charset to be returned
* if an 8-bit Charset is encountered.
*/
public void setDefaultCharset(Charset defaultCharset) {
if (defaultCharset != null)
this.defaultCharset = defaultCharset;
else
this.defaultCharset = getDefaultSystemCharset();
}
public Charset getCharset() {
if (this.charset == null)
this.charset = guessEncoding();
return charset;
}
/**
* 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.
*
* @param enforce a boolean specifying the use or not of US-ASCII.
*/
public void setEnforce8Bit(boolean enforce) {
this.enforce8Bit = enforce;
}
/**
* Gets the enforce8Bit flag, in case we do not want to ever get a US-ASCII encoding.
*
* @return a boolean representing the flag of use of US-ASCII.
*/
public boolean getEnforce8Bit() {
return this.enforce8Bit;
}
/**
* Retrieves the default Charset
*/
public Charset getDefaultCharset() {
return defaultCharset;
}
/**
* Guess the encoding of the provided buffer.
* If Byte Order Markers are encountered at the beginning of the buffer, we immediately
* 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.
*
* @return the Charset recognized.
*/
private Charset guessEncoding() {
// if the file has a Byte Order Marker, we can assume the file is in UTF-xx
// otherwise, the file would not be human readable
if (hasUTF8Bom())
return Charset.forName("UTF-8");
if (hasUTF16LEBom())
return Charset.forName("UTF-16LE");
if (hasUTF16BEBom())
return Charset.forName("UTF-16BE");
// if a byte has its most significant bit set, the file is in UTF-8 or in the default encoding
// otherwise, the file is in US-ASCII
boolean highOrderBit = false;
// if the file is in UTF-8, high order bytes must have a certain value, in order to be valid
// if it's not the case, we can assume the encoding is the default encoding of the system
boolean validU8Char = true;
// TODO the buffer is not read up to the end, but up to length - 6
int length = buffer.length;
int i = 0;
while (i < length - 6) {
byte b0 = buffer[i];
byte b1 = buffer[i + 1];
byte b2 = buffer[i + 2];
byte b3 = buffer[i + 3];
byte b4 = buffer[i + 4];
byte b5 = buffer[i + 5];
if (b0 < 0) {
// a high order bit was encountered, thus the encoding is not US-ASCII
// it may be either an 8-bit encoding or UTF-8
highOrderBit = true;
// a two-bytes sequence was encountered
if (isTwoBytesSequence(b0)) {
// there must be one continuation byte of the form 10xxxxxx,
// otherwise the following character is is not a valid UTF-8 construct
if (!isContinuationChar(b1))
validU8Char = false;
else
i++;
}
// a three-bytes sequence was encountered
else if (isThreeBytesSequence(b0)) {
// there must be two continuation bytes of the form 10xxxxxx,
// otherwise the following character is is not a valid UTF-8 construct
if (!(isContinuationChar(b1) && isContinuationChar(b2)))
validU8Char = false;
else
i += 2;
}
// a four-bytes sequence was encountered
else if (isFourBytesSequence(b0)) {
// there must be three continuation bytes of the form 10xxxxxx,
// otherwise the following character is is not a valid UTF-8 construct
if (!(isContinuationChar(b1) && isContinuationChar(b2) && isContinuationChar(b3)))
validU8Char = false;
else
i += 3;
}
// a five-bytes sequence was encountered
else if (isFiveBytesSequence(b0)) {
// there must be four continuation bytes of the form 10xxxxxx,
// otherwise the following character is is not a valid UTF-8 construct
if (!(isContinuationChar(b1)
&& isContinuationChar(b2)
&& isContinuationChar(b3)
&& isContinuationChar(b4)))
validU8Char = false;
else
i += 4;
}
// a six-bytes sequence was encountered
else if (isSixBytesSequence(b0)) {
// there must be five continuation bytes of the form 10xxxxxx,
// otherwise the following character is is not a valid UTF-8 construct
if (!(isContinuationChar(b1)
&& isContinuationChar(b2)
&& isContinuationChar(b3)
&& isContinuationChar(b4)
&& isContinuationChar(b5)))
validU8Char = false;
else
i += 5;
}
else
validU8Char = false;
}
if (!validU8Char)
break;
i++;
}
// if no byte with an high order bit set, the encoding is US-ASCII
// (it might have been UTF-7, but this encoding is usually internally used only by mail systems)
if (!highOrderBit) {
// returns the default charset rather than US-ASCII if the enforce8Bit flag is set.
if (this.enforce8Bit)
return this.defaultCharset;
else
return Charset.forName("US-ASCII");
}
// if no invalid UTF-8 were encountered, we can assume the encoding is UTF-8,
// otherwise the file would not be human readable
if (validU8Char)
return Charset.forName("UTF-8");
// finally, if it's not UTF-8 nor US-ASCII, let's assume the encoding is the default encoding
return this.defaultCharset;
}
/**
* If the byte has the form 10xxxxx, then it's a continuation byte of a multiple byte character;
*
* @param b a byte.
* @return true if it's a continuation char.
*/
private static boolean isContinuationChar(byte b) {
return -128 <= b && b <= -65;
}
/**
* If the byte has the form 110xxxx, then it's the first byte of a two-bytes sequence character.
*
* @param b a byte.
* @return true if it's the first byte of a two-bytes sequence.
*/
private static boolean isTwoBytesSequence(byte b) {
return -64 <= b && b <= -33;
}
/**
* If the byte has the form 1110xxx, then it's the first byte of a three-bytes sequence character.
*
* @param b a byte.
* @return true if it's the first byte of a three-bytes sequence.
*/
private static boolean isThreeBytesSequence(byte b) {
return -32 <= b && b <= -17;
}
/**
* If the byte has the form 11110xx, then it's the first byte of a four-bytes sequence character.
*
* @param b a byte.
* @return true if it's the first byte of a four-bytes sequence.
*/
private static boolean isFourBytesSequence(byte b) {
return -16 <= b && b <= -9;
}
/**
* If the byte has the form 11110xx, then it's the first byte of a five-bytes sequence character.
*
* @param b a byte.
* @return true if it's the first byte of a five-bytes sequence.
*/
private static boolean isFiveBytesSequence(byte b) {
return -8 <= b && b <= -5;
}
/**
* If the byte has the form 1110xxx, then it's the first byte of a six-bytes sequence character.
*
* @param b a byte.
* @return true if it's the first byte of a six-bytes sequence.
*/
private static boolean isSixBytesSequence(byte b) {
return -4 <= b && b <= -3;
}
/**
* Retrieve the default charset of the system.
*
* @return the default Charset.
*/
public static Charset getDefaultSystemCharset() {
return Charset.forName(System.getProperty("file.encoding"));
}
/**
* Has a Byte Order Marker for UTF-8 (Used by Microsoft's Notepad and other editors).
*
* @return true if the buffer has a BOM for UTF8.
*/
public boolean hasUTF8Bom() {
if (buffer.length >= 3)
return (buffer[0] == -17 && buffer[1] == -69 && buffer[2] == -65);
else
return false;
}
/**
* Has a Byte Order Marker for UTF-16 Low Endian
* (ucs-2le, ucs-4le, and ucs-16le).
*
* @return true if the buffer has a BOM for UTF-16 Low Endian.
*/
public boolean hasUTF16LEBom() {
if (buffer.length >= 2)
return (buffer[0] == -1 && buffer[1] == -2);
else
return false;
}
/**
* Has a Byte Order Marker for UTF-16 Big Endian
* (utf-16 and ucs-2).
*
* @return true if the buffer has a BOM for UTF-16 Big Endian.
*/
public boolean hasUTF16BEBom() {
if (buffer.length >= 2)
return (buffer[0] == -2 && buffer[1] == -1);
else
return false;
}
/**
* Gets a BufferedReader (indeed a LineNumberReader) from the File
* specified in the constructor of CharsetToolkit using the charset discovered or the default
* charset if an 8-bit Charset is encountered.
*
* @return a BufferedReader
* @throws FileNotFoundException if the file is not found.
*/
public BufferedReader getReader() throws FileNotFoundException {
LineNumberReader reader = new LineNumberReader(new InputStreamReader(new FileInputStream(file), getCharset()));
if (hasUTF8Bom() || hasUTF16LEBom() || hasUTF16BEBom()) {
try {
reader.read();
}
catch (IOException e) {
// should never happen, as a file with no content
// but with a BOM has at least one char
}
}
return reader;
}
/**
* Retrieves all the available Charsets on the platform,
* among which the default charset.
*
* @return an array of Charsets.
*/
public static Charset[] getAvailableCharsets() {
Collection collection = Charset.availableCharsets().values();
return (Charset[]) collection.toArray(new Charset[collection.size()]);
}
}