UnicodeDetector.java

/*
 * UnicodeDetector,  <enter purpose here>.
 * Copyright (C) 2005  Achim Westermann, Achim.Westermann@gmx.de
 *
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 * 
 * The contents of this collection are subject to the Mozilla Public License Version 
 * 1.1 (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.mozilla.org/MPL/
 * 
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 * 
 * The Original Code is the cpDetector code in [sub] packages info.monitorenter and 
 * cpdetector. 
 * 
 * The Initial Developer of the Original Code is
 * Achim Westermann <achim.westermann@gmx.de>.
 * 
 * Portions created by the Initial Developer are Copyright (c) 2007 
 * the Initial Developer. All Rights Reserved.
 * 
 * Contributor(s):
 * 
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 * 
 * ***** END LICENSE BLOCK ***** * 
 *  
 * If you modify or optimize the code in a useful way please let me know.
 * Achim.Westermann@gmx.de
 */
package info.monitorenter.cpdetector.io;

import info.monitorenter.cpdetector.io.AbstractCodepageDetector;
import info.monitorenter.cpdetector.io.ICodepageDetector;
import info.monitorenter.cpdetector.io.UnknownCharset;

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.nio.charset.Charset;


public class UnicodeDetector extends AbstractCodepageDetector {
    private static ICodepageDetector instance;

    /**
     * Singleton constructor
     */
    private UnicodeDetector() {
        super();
    }

    public static ICodepageDetector getInstance() {
        if (instance == null) {
            instance = new UnicodeDetector();
        }
        return instance;
    }

    /*
     * (non-Javadoc) It is assumed that the inputstream is at the start of the file or String (in order to read the
     * BOM).
     * 
     * @see cpdetector.io.ICodepageDetector#detectCodepage(java.io.InputStream, int)
     * 
     */
    public Charset detectCodepage(InputStream in, int length) throws IOException {
        byte[] bom = new byte[4]; // Get the byte-order mark, if there is one
        in.read(bom, 0, 4);
        // Unicode formats => read BOM
        byte b = (byte)0xEF;
        if (bom[0] == (byte)0x00 && bom[1] == (byte)0x00 && bom[2] == (byte)0xFE
                && bom[2] == (byte)0xFF) // utf-32BE
            return Charset.forName("UTF-32BE");
        if (bom[0] == (byte)0xFF && bom[1] == (byte)0xFE && bom[2] == (byte)0x00
                && bom[2] == (byte)0x00) // utf-32BE
            return Charset.forName("UTF-32LE");
        if (bom[0] == (byte)0xEF && bom[1] == (byte)0xBB && bom[2] == (byte)0xBF) // utf-8
            return Charset.forName("UTF-8");
        if (bom[0] == (byte)0xff && bom[1] == (byte)0xfe) // ucs-2le, ucs-4le, and ucs-16le
            return Charset.forName("UTF-16LE");
        if (bom[0] == (byte)0xfe && bom[1] == (byte)0xff) // utf-16 and ucs-2
            return Charset.forName("UTF-16BE");
        if (bom[0] == (byte)0 && bom[1] == (byte)0 && bom[2] == (byte)0xfe && bom[3] == (byte)0xff) // ucs-4
            return Charset.forName("UCS-4");
        return UnknownCharset.getInstance();
    }

    /**
     * @see info.monitorenter.cpdetector.io.ICodepageDetector#detectCodepage(java.net.URL)
     */
    public Charset detectCodepage(final URL url) throws IOException {
        Charset result;
        BufferedInputStream in = new BufferedInputStream(url.openStream());
        result = this.detectCodepage(in, Integer.MAX_VALUE);
        in.close();
        return result;
    }

}