java 将long或int转换为62进制的字符串，可用于短链生成

短链生成方法，将自增的ID转化为62进制字符串即可缩短长度。 

package com.urlservices.common;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

//自定义数值跟字符串的映射
public class ShortURLHelper {
	private static Logger logger = LoggerFactory.getLogger(ShortURLHelper.class);
	// 自定62进制义字符
	private final static String sp = "iBCW3eQs5RJagMT7nOX8f2ozwGKxDZFbuNLSlYVIt4q6Ay1cP0Urkjmp9hvdEH";
	private final static int radix = sp.length();

	/**
	 * 将自定义62进制的字符串转为10进制long
	 * 
	 * @param str
	 * @return
	 */
	public static long StrToNum(String str) {
		try {
			long result = 0;
			for (int i = 0; i < str.length(); i++) {
				result += sp.indexOf(str.charAt(i)) * Math.pow(radix, i);
			}
			return result;
		} catch (Exception ex) {
			logger.error("将code转为long异常,input:"+str+",ex:"+ex.getMessage());
			ex.printStackTrace();
			return -1;
		}
	}

	/**
	 * 将10进制的数值转换为自定义的62进制的字符串
	 * 
	 * @param num
	 * @return
	 */
	public static String NumToStr(long num) {
		try {
			if (num < 0) {
				return null;
			}
			StringBuilder buf = new StringBuilder();
			int remainder = 0;
			do {
				remainder = (int) (num % radix);// 求余数
				num = num / radix;// 除以基数
				buf.append(sp.charAt(remainder));// 保存余数，记得要倒叙排列
			} while (num != 0);
			return buf.toString();
		} catch (Exception ex) {
			logger.error("将long转为code异常,input:"+num+",ex:"+ex.getMessage());
			return null;
		}
	}

	public static void main(String[] args) {
		for (int i = 0; i < 50000; i++)
			System.out.println(i + "--" + NumToStr(i) + "--" + StrToNum(NumToStr(i)));
	}
}