Zero padding before or after the string

public static String addZeroForNum(String str, int strLength) {  
    int strLen = str.length();  
    if (strLen < strLength) {  
        while (strLen < strLength) {  
            StringBuffer sb = new StringBuffer();  
            sb.append("0").append(str);// 左补0  
            // sb.append(str).append("0");//右补0  
            str = sb.toString();  
            strLen = str.length();  
        }  
    }  
  
    return str;  
}