Byte Order Mark Utility

BOMUtil.java

import java.io.*;

/** Source: http://bugs.java.com/bugdatabase/view_bug.do?bug_id=6206835 */
public class BOMUtil {
    public final static int NONE=-1;
    public final static int UTF32BE=0;
    public final static int UTF32LE=1;
    public final static int UTF16BE=2;
    public final static int UTF16LE=3;
    public final static int UTF8=4;

    public final static byte[] UTF32BEBOMBYTES = new byte[]{(byte)0x00 ,(byte)0x00 ,(byte)0xFE ,(byte)0xFF ,};
    public final static byte[] UTF32LEBOMBYTES = new byte[]{(byte)0xFF ,(byte)0xFE ,(byte)0x00 ,(byte)0x00 ,};
    public final static byte[] UTF16BEBOMBYTES = new byte[]{(byte)0xFE ,(byte)0xFF ,};
    public final static byte[] UTF16LEBOMBYTES = new byte[]{(byte)0xFF ,(byte)0xFE ,};
    public final static byte[] UTF8BOMBYTES    = new byte[]{(byte)0xEF ,(byte)0xBB ,(byte)0xBF ,};

    public final static byte[][] BOMBYTES=new byte[][]{
            UTF32BEBOMBYTES,
            UTF32LEBOMBYTES,
            UTF16BEBOMBYTES,
            UTF16LEBOMBYTES,
            UTF8BOMBYTES,
    };

    public final static int MAXBOMBYTES=4;//no bom sequence is longer than 4 byte

    public static int getBOMType(byte[] _bomBytes){
        return getBOMType(_bomBytes,_bomBytes.length);
    }

    public static int getBOMType(byte[] _bomBytes, int _length){
        for (int i = 0; i < BOMBYTES.length; i++) {
            for(int j=0; j<_length && j<BOMBYTES[i].length; j++){
                if(_bomBytes[j]!=BOMBYTES[i][j]) break;
                if(_bomBytes[j]==BOMBYTES[i][j] && j==BOMBYTES[i].length-1) return i;
            }
        }
        return NONE;
    }

    public static int getBOMType(File _f) throws IOException{
        FileInputStream fIn=new FileInputStream(_f);
        byte[] buff=new byte[MAXBOMBYTES];
        int read=fIn.read(buff);
        int BOMType=getBOMType(buff,read);
        fIn.close();
        return BOMType;
    }

    public static String getFirstBytes(File _f) throws IOException{
        FileInputStream fIn=new FileInputStream(_f);
        byte[] buff=new byte[MAXBOMBYTES];
        fIn.read(buff);
        String read = "";
        for (int i = 0; i < buff.length; i++) {
            read += String.format("%02x", buff[i]) + " ";
        }
        fIn.close();
        return read;
    }

    public static int getSkipBytes(int BOMType){
        if(BOMType<0 || BOMType>=BOMBYTES.length) return 0;
        return BOMBYTES[BOMType].length;
    }

    /**
     * Just reads necessary bytes from the stream
     * @param _fIn
     */
    public static Reader getReader(File _f, String encoding) throws IOException{
        int BOMType=getBOMType(_f);
        int skipBytes=getSkipBytes(BOMType);
        FileInputStream fIn=new FileInputStream(_f);
        fIn.skip(skipBytes);
        Reader reader=new InputStreamReader(fIn,encoding);
        return reader;
    }
}