URL短地址压缩算法 微博短地址原理解析(再转与Java实现)

主要是一次发新浪微博，发网址时看到网址被压缩了，才对这个有兴趣，于是查了查，查到这些

URL短地址压缩算法 微博短地址原理解析

和其Java实现的博文

URL短地址压缩算法 微博短地址原理解析 （Java实现）

对第一篇博文，留了疑问，主要是觉得于四个得到的压缩地址中取一个，那之前循环计算不是有些浪费计算能力吗？

不多说废话，这里就贴下自己的Java验证实现代码：

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.io.*;

public class ShortUrl{
	public static void main(String[] args){
		String url = "http://www.sunchis.com";
		for(String string:ShortText(url)){
			print(string);
		}
	}
	public static String[] ShortText(String string){
		String key = "XuLiang";			//自定义生成MD5加密字符串的混合KEY
		String[] chars = new String[]{		//要使用生成URL的字符
			"a","b","c","d","e","f","g","h",
			"i","j","k","l","m","n","o","p",
			"q","r","s","t","u","v","w","x",
			"y","z", "0","1","2","3","4","5",
			"6","7","8","9","A","B","C","D",
			"E","F","G","H","I","J","K","L",
			"M","N","O","P","Q","R","S","T",
			"U","V", "W","X","Y","Z"
		};
		String hex = MD5Encode(key + string);
		int hexLen = hex.length();
		int subHexLen = hexLen/8;
		String[] ShortStr = new String[4];

		for(int i = 0;i < subHexLen;i++){
			String outChars = "";
			int j = i+1;
			String subHex = hex.substring(i*8,j*8);
			long idx = Long.valueOf("3FFFFFFF",16) & Long.valueOf(subHex,16);
			
			for(int k = 0;k < 6;k++){
				int index = (int)(Long.valueOf("0000003D",16) & idx);//这里取5位没有要求吗？不是取连续的5位
				outChars += chars[index];
				idx = idx >> 5;
			}
			ShortStr[i] = outChars;
		}
		return ShortStr;
	}

	private final static String[] hexDigits = {
		"0","1","2","3","4","5","6","7",
		"8","9","a","b","c","d","e","f"
	};
	public static String byteArrayToHexString(byte[] b){
		StringBuffer resultSb = new StringBuffer();
		for(int i = 0;i < b.length;i++){
			resultSb.append(byteToHexString(b[i]));
		}
		return resultSb.toString();
	}
	
	private static String byteToHexString(byte b){
		int n = b;
		if(n < 0)
			n = 256 + n;
		int d1 = n / 16;
		int d2 = n % 16;
		return hexDigits[d1] + hexDigits[d2];
	}

	public static String MD5Encode(String origin){
		String resultString = null;
		try{
			resultString = new String(origin);
			MessageDigest md = MessageDigest.getInstance("MD5");

			resultString.trim();

			resultString = byteArrayToHexString(md.digest(resultString.getBytes("UTF-8")));
		}catch(Exception ex){}
		return resultString;
	}

	private static void print(Object messagr){
		System.out.println(messagr);
	}
}