判断文件编码

public static String get_charset( File file ) {   
        String charset = "GBK";   
        byte[] first3Bytes = new byte[3];   
        try {   
            boolean;   
            BufferedInputStream bis = new BufferedInputStream( new FileInputStream( file ) );   
            bis.mark( 0 );   
            int read = bis.read( first3Bytes, 0, 3 );   
            if ( read == -1 ) return charset;   
            if ( first3Bytes[0] == (byte) 0xFF && first3Bytes[1] == (byte) 0xFE ) {   
                charset = "UTF-16LE";   
                checked = true;   
            }   
            else if ( first3Bytes[0] == (byte) 0xFE && first3Bytes[1] == (byte) 0xFF ) {   
                charset = "UTF-16BE";   
                checked = true;   
            }   
            else if ( first3Bytes[0] == (byte) 0xEF && first3Bytes[1] == (byte) 0xBB && first3Bytes[2] == (byte) 0xBF ) {   
                charset = "UTF-8";   
                checked = true;   
            }   
            bis.reset();   
            if ( !checked ) {   
            //    int len = 0;   
                int loc = 0;   
  
                while ( (read = bis.read()) != -1 ) {   
                    loc++;   
                    if ( read >= 0xF0 ) break;   
                    if ( 0x80 <= read && read <= 0xBF ) // 单独出现BF以下的，也算是GBK   
                    break;   
                    if ( 0xC0 <= read && read <= 0xDF ) {   
                        read = bis.read();   
                        if ( 0x80 <= read && read <= 0xBF ) // 双字节 (0xC0 - 0xDF) (0x80   
                                                                        // - 0xBF),也可能在GB编码内   
                        continue;   
                        else break;   
                    }   
                    else if ( 0xE0 <= read && read <= 0xEF ) {// 也有可能出错，但是几率较小   
                        read = bis.read();   
                        if ( 0x80 <= read && read <= 0xBF ) {   
                            read = bis.read();   
                            if ( 0x80 <= read && read <= 0xBF ) {   
                                charset = "UTF-8";   
                                break;   
                            }   
                            else break;   
                        }   
                        else break;   
                    }   
                }   
                //System.out.println( loc + " " + Integer.toHexString( read ) );   
            }   
  
            bis.close();   
        } catch ( Exception e ) {   
            e.printStackTrace();   
        }   
  
        return charset;   
    }