public void getInt(String str){
   String[] arr = str.split("[^0-9]");
   String s = "";
   for(int i=0;i<arr.lenght;i++){
      s+=arr[i];
   }
}

------解决方案--------------------
1.读取一行，放到变量line里面；
2.line = line.replaceAll("\\D", "");
3.line就是纯数字了。

------解决方案--------------------
Java code

    public static void main(String[] args) {
        String str = "201 一般公共服务 "         + "\r\n" +
                    "202 外交"                  + "\r\n" +
                    "2040101"                  + "\r\n" +
                    "2010303"                   + "\r\n" +
                    "201 一般公共服务"          + "\r\n" +
                    "202 外交"                 + "\r\n" +
                    "2040101"                  + "\r\n" +
                    "2010303"                 + "\r\n"
        ;
        Matcher matcher = Pattern.compile("\\d+").matcher(str);
        while (matcher.find()) {
            System.out.println(matcher.group());
        }
    }