将数字转换为汉字书写模式

面试i遇到这样一个题：

将23009912340转换为"二百三十亿零九百九十一万二千三百四十"，当时没想到什么好的方法，个人感觉"零"最难处理,代码如下:

import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class ToChina {

    public static final String[] st = new String[] { "千", "百", "十", "" };

    public String convert(int i) {
        String china = null;
        switch (i) {
        case 0:
            china = "零";
            break;
        case 1:
            china = "一";
            break;
        case 2:
            china = "二";
            break;
        case 3:
            china = "三";
            break;
        case 4:
            china = "四";
            break;
        case 5:
            china = "五";
            break;
        case 6:
            china = "六";
            break;
        case 7:
            china = "七";
            break;
        case 8:
            china = "八";
            break;
        case 9:
            china = "九";
            break;
        }
        return china;
    }

    public Map<String, Boolean> buildComplete(String s) {
        char[] chars = s.toCharArray();
        String[] strs = new String[] { null, null, null, null };
        int nullnum = 4 - s.length();
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < chars.length; i++) {
            strs[i + nullnum] = String.valueOf(chars[i]);
        }
        Boolean flag = false;
        Boolean f = false;
        for (int i = strs.length - 1; i >= 0; i--) {
            if (f == false && strs[i] != null && strs[i].equals("零")) {
                strs[i] = null;
                flag = true;
            }
            if (strs[i] != null && !strs[i].equals("零")) {
                f = true;
                break;
            }

        }
        Boolean b = false;
        for (int i = 0; i < 4; i++) {
            if (strs[i] != null) {
                if (!strs[i].equals("零")) {
                    sb.append(strs[i] + st[i]);
                }
                if (strs[i].equals("零") && b == false) {
                    sb.append(strs[i]);
                    b = true;
                }
            }
        }
        Map<String, Boolean> map = new HashMap<String, Boolean>();
        map.put(sb.toString(), flag);
        return map;
    }

    public String[] split(String str) {
        int length = str.length();
        int num = length / 4;
        int mo = length % 4;
        String[] ss = mo > 0 ? new String[num + 1] : new String[num];
        if (length <= 4) {
            ss = new String[] { str };
        } else {
            for (int i = 0; i < ss.length; i++) {
                if (i == 0) {
                    ss[i] = str.substring(0, mo);
                } else {
                    ss[i] = str.substring(mo + (i - 1) * 4, mo + (i) * 4);
                }
            }
        }
        return ss;
    }

    public String danwei(Map<String, Boolean> map, int i, Boolean flag) {
        String v = null;
        if (i == 3) {
            v = "兆";
        }
        if (i == 2) {
            v = "亿";
        }
        if (i == 1) {
            v = "万";
        }
        if (i == 0) {
            v = "";
        }
        StringBuffer sb = new StringBuffer();
        Set<String> keyset = map.keySet();
        for (String key : keyset) {
            if (!key.equals("")) {
                sb.append(key);
                sb.append(v);
                if (map.get(key) == true && i != 0) {
                    sb.append("零");
                }
                if (flag == true) {
                    sb.deleteCharAt(0);
                }
            }
        }
        return sb.toString();
    }

    public String result(String str) {
        StringBuffer sb = new StringBuffer();
        String[] strs = this.split(this.convertAll(str));
        int k = 1;
        for (int i = 0; i < strs.length; i++) {
            int j = strs.length - k;
            k += 1;
            boolean flag = false;
            if (i - 1 >= 0) {
                Map map = this.buildComplete(strs[i - 1]);
                Set<String> keyset = map.keySet();
                for (String key : keyset) {
                    flag = (Boolean) map.get(key);
                    break;
                }
            }
            String s = this.danwei(this.buildComplete(strs[i]), j, flag);
            sb.append(s);
        }
        return sb.toString();
    }

    public String convertAll(String str) {
        char[] chars = str.toCharArray();
        String[] cs = new String[chars.length];
        for (int i = 0; i < chars.length; i++) {
            cs[i] = this.convert(Integer.valueOf(String.valueOf(chars[i])));
        }
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < cs.length; i++) {
            sb.append(cs[i]);
        }
        return sb.toString();
    }

    public static void main(String[] args) {
        ToChina t = new ToChina();
        System.out.print(t.result("23009912340"));
    }

}