获取文件的编码方式

public static String codeString(String fileName) throws Exception{  
    BufferedInputStream bin = new BufferedInputStream(  
    new FileInputStream(fileName));  
    int p = (bin.read() << 8) + bin.read();  
    String code = null;  
      
    switch (p) {  
        case 0xefbb:  
            code = "UTF-8";  
            break;  
        case 0xfffe:  
            code = "Unicode";  
            break;  
        case 0xfeff:  
            code = "UTF-16BE";  
            break;  
        default:  
            code = "GBK";  
    }  
      
    return code;  
}