手机号、银行卡号等掩码处理（优化）

public class StartUtils {

    /**
     * 掩码转换规则
     * @param len
     * @return
     */
    public static Map convertToStartRule(int len) {
        Map m = new HashMap();
        String indexRule ="";
        switch (len) {
            case 9:
            {
                indexRule="4|1";
                break;
            }
            case 10:
            {
                indexRule="3|3";
                break;
            }
            case 11:
            {
                indexRule="3|4";
                break;
            }
            case 12:
            {
                indexRule="4|4";
                break;
            }
            case 13:
            {
                indexRule="4|5";
                break;
            }
            case 14:
            {
                indexRule="4|6";
                break;
            }
            case 15:{
                indexRule="4|7";
                break;
            }
            case 16:
            {
                indexRule="4|8";
                break;
            }
            case 17:
            {
                indexRule="4|9";
                break;
            }
            case 18:
            {
                indexRule="4|10";
                break;
            }
            case 19: {
                indexRule="4|11";
                break;
            }
            default:{
                if(len>3) {
                    int mol = len % 4;
                    int s=len/4;
                    indexRule=s+"|"+(2*s+mol);
                }else {
                    indexRule="0|1";
                }
                break;
            }
        }
        m.put(len,indexRule);
        return m;
    }


    /**
     * 转换成掩码
     * @param str
     * @return
     */
    public static String convertToStart(String str) {
        String result = str;
        int len = str.length();
        Map mapRule=convertToStartRule(len);
        String ruleStr=mapRule.get(len);
        String[] ruleArr=ruleStr.split("\\|");
        int frontIndex=Integer.parseInt( ruleArr[0]);
        int subLength=Integer.parseInt(ruleArr[1]);
        String frontStr= str.substring(0,frontIndex);
        String backStr=str.substring(frontIndex+subLength,len);
        result=frontStr+printStart(subLength)+backStr;
        return result;
    }

    /**
     * 打印掩码个数
     * @param subLength
     * @return
     */
    public static String printStart(int subLength) {
        String start = "";
        for(int i=0;i