guess Encoding - Java Internationalization

Description

guess Encoding
Demo Code

/*/*from w  ww .ja v  a2  s  .  co m*/
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 * 
 * Copyright 2011 OpenConcerto, by ILM Informatique. All rights reserved.
 * 
 * The contents of this file are subject to the terms of the GNU General Public License Version 3
 * only ("GPL"). You may not use this file except in compliance with the License. You can obtain a
 * copy of the License at http://www.gnu.org/licenses/gpl-3.0.html See the License for the specific
 * language governing permissions and limitations under the License.
 * 
 * When distributing the software, include this License Header Notice in each file.
 */
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.nio.charset.Charset;
import java.util.Collection;

public class Main{
    public static void main(String[] argv) throws Exception{
        System.out.println(guessEncoding());
    }
    private boolean enforce8Bit;
    public Charset guessEncoding() {
        if (hasUTF8Bom(buffer))
            return Charset.forName("UTF-8");
        if (hasUTF16LEBom(buffer))
            return Charset.forName("UTF-16LE");
        if (hasUTF16BEBom(buffer))
            return Charset.forName("UTF-16BE");
        boolean highOrderBit = false;
        boolean validU8Char = true;
        int length = buffer.length;
        int i = 0;
        do {
            if (i >= length - 6)
                break;
            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) {
                highOrderBit = true;
                if (isTwoBytesSequence(b0)) {
                    if (!isContinuationChar(b1))
                        validU8Char = false;
                    else
                        i++;
                } else if (isThreeBytesSequence(b0)) {
                    if (!isContinuationChar(b1) || !isContinuationChar(b2))
                        validU8Char = false;
                    else
                        i += 2;
                } else if (isFourBytesSequence(b0)) {
                    if (!isContinuationChar(b1) || !isContinuationChar(b2)
                            || !isContinuationChar(b3))
                        validU8Char = false;
                    else
                        i += 3;
                } else if (isFiveBytesSequence(b0)) {
                    if (!isContinuationChar(b1) || !isContinuationChar(b2)
                            || !isContinuationChar(b3)
                            || !isContinuationChar(b4))
                        validU8Char = false;
                    else
                        i += 4;
                } else if (isSixBytesSequence(b0)) {
                    if (!isContinuationChar(b1) || !isContinuationChar(b2)
                            || !isContinuationChar(b3)
                            || !isContinuationChar(b4)
                            || !isContinuationChar(b5))
                        validU8Char = false;
                    else
                        i += 5;
                } else {
                    validU8Char = false;
                }
            }
            if (!validU8Char)
                break;
            i++;
        } while (true);
        if (!highOrderBit)
            if (enforce8Bit)
                return defaultCharset;
            else
                return Charset.forName("US-ASCII");
        if (validU8Char)
            return Charset.forName("UTF-8");
        else
            return defaultCharset;
    }
    public static Charset guessEncoding(File f, int bufferLength)
            throws FileNotFoundException, IOException {
        return guessEncoding(f, bufferLength, null);
    }
    public static Charset guessEncoding(File f, int bufferLength,
            Charset defaultCharset) throws FileNotFoundException,
            IOException {
        FileInputStream fis = new FileInputStream(f);
        byte buffer[] = new byte[bufferLength];
        fis.read(buffer);
        fis.close();
        CharsetHelper toolkit = new CharsetHelper(buffer);
        if (defaultCharset != null) {
            toolkit.setDefaultCharset(defaultCharset);
        }
        return toolkit.guessEncoding();
    }
    private static boolean hasUTF8Bom(byte bom[]) {
        return bom[0] == -17 && bom[1] == -69 && bom[2] == -65;
    }
    private static boolean hasUTF16LEBom(byte bom[]) {
        return bom[0] == -1 && bom[1] == -2;
    }
    private static boolean hasUTF16BEBom(byte bom[]) {
        return bom[0] == -2 && bom[1] == -1;
    }
    private static boolean isTwoBytesSequence(byte b) {
        return -64 <= b && b <= -33;
    }
    private static boolean isContinuationChar(byte b) {
        return -128 <= b && b <= -65;
    }
    private static boolean isThreeBytesSequence(byte b) {
        return -32 <= b && b <= -17;
    }
    private static boolean isFourBytesSequence(byte b) {
        return -16 <= b && b <= -9;
    }
    private static boolean isFiveBytesSequence(byte b) {
        return -8 <= b && b <= -5;
    }
    private static boolean isSixBytesSequence(byte b) {
        return -4 <= b && b <= -3;
    }
    public void setDefaultCharset(Charset defaultCharset) {
        if (defaultCharset != null)
            this.defaultCharset = defaultCharset;
        else
            this.defaultCharset = getDefaultSystemCharset();
    }
    public static Charset getDefaultSystemCharset() {
        return Charset.forName(System.getProperty("file.encoding"));
    }
}
guess Encoding - Java Internationalization

Description

Demo Code

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