【转】微博URL短网址生成算法原理及（java版、php版实现实例）

微博URL短网址生成算法原理及（java版、php版实现实例）

算法二

a-zA-Z0-9 这64位取6位组合,可产生500多亿个组合数量.把数字和字符组合做一定的映射,就可以产生唯一的字符串,如第62个组合就是aaaaa9,第63个组合就是aaaaba,再利用洗牌算法，把原字符串打乱后保存，那么对应位置的组合字符串就会是无序的组合。

把长网址存入数据库,取返回的id,找出对应的字符串,例如返回ID为1，那么对应上面的字符串组合就是bbb,同理 ID为2时，字符串组合为bba,依次类推,直至到达64种组合后才会出现重复的可能，所以如果用上面的62个字符，任意取6个字符组合成字符串的话，你的数据存量达到500多亿后才会出现重复的可能。

具体参看这里彻底完善新浪微博接口和超短URL算法,算法四可以算作是此算法的一种实现,此算法一般不会重复,但是如果是统计的话,就有很大问题,特别是对域名相关的统计,就抓瞎了。

public class ShortUrlGenerator {

/**
* @param args
*/
public static void main(String[] args) {

String sLongUrl = "http://474515923.qzone.qq.com" ; //长链接
String[] aResult = shortUrl (sLongUrl);
// 打印出结果
for ( int i = 0; i < aResult. length ; i++) {
System. out .println( "[" + i + "]:::" + aResult[i]);
}
}

public static String[] shortUrl(String url) {
// 可以自定义生成 MD5 加密字符传前的混合 KEY
String key = "mengdelong" ;
// 要使用生成 URL 的字符
String[] chars = new String[] { "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"

};
// 对传入网址进行 MD5 加密
String sMD5EncryptResult = ( new CMyEncrypt()).md5(key + url);
String hex = sMD5EncryptResult;

String[] resUrl = new String[4];
for ( int i = 0; i < 4; i++) {

// 把加密字符按照 8 位一组 16 进制与 0x3FFFFFFF 进行位与运算
String sTempSubString = hex.substring(i * 8, i * 8 + 8);

// 这里需要使用 long 型来转换，因为 Inteper .parseInt() 只能处理 31 位 , 首位为符号位 , 如果不用 long ，则会越界
long lHexLong = 0x3FFFFFFF & Long.parseLong (sTempSubString, 16);
String outChars = "" ;
for ( int j = 0; j < 6; j++) {
// 把得到的值与 0x0000003D 进行位与运算，取得字符数组 chars 索引
long index = 0x0000003D & lHexLong;
// 把取得的字符相加
outChars += chars[( int ) index];
// 每次循环按位右移 5 位
lHexLong = lHexLong >> 5;
}
// 把字符串存入对应索引的输出数组
resUrl[i] = outChars;
}
return resUrl;
}
}

跳转原理

当我们生成短链接之后，只需要在表中（数据库或者NoSql ）存储原始链接与短链接的映射关系即可。当我们访问短链接时，只需要从映射关系中找到原始链接，即可跳转到原始链接。

附：控制长度？

package testjava;

import java.util.HashMap;
import java.util.Random;

/*
* URL Shortener
*/
public class URLShortener {
// storage for generated keys
private HashMap<String, String> keyMap; // key-url map
private HashMap<String, String> valueMap;// url-key map to quickly check
// whether an url is
// already entered in our system
private String domain; // Use this attribute to generate urls for a custom
// domain name defaults to http://fkt.in private char myChars[]; // This array is used for character to number
// mapping
private Random myRand; // Random object used to generate random integers
private int keyLength; // the key length in URL defaults to 8

// Default Constructor
URLShortener() {
keyMap = new HashMap<String, String>();
valueMap = new HashMap<String, String>();
myRand = new Random();
keyLength = 8;
myChars = new char[62];
for (int i = 0; i < 62; i++) {
int j = 0;
if (i < 10) {
j = i + 48;
} else if (i > 9 && i <= 35) {
j = i + 55;
} else {
j = i + 61;
}
myChars[i] = (char) j;
}
domain = "http://fkt.in";
}

// Constructor which enables you to define tiny URL key length and base URL
// name
URLShortener(int length, String newDomain) {
this();
this.keyLength = length;
if (!newDomain.isEmpty()) {
newDomain = sanitizeURL(newDomain);
domain = newDomain;
}
}

// shortenURL
// the public method which can be called to shorten a given URL
public String shortenURL(String longURL) {
String shortURL = "";
if (validateURL(longURL)) {
longURL = sanitizeURL(longURL);
if (valueMap.containsKey(longURL)) {
shortURL = domain + "/" + valueMap.get(longURL);
} else {
shortURL = domain + "/" + getKey(longURL);
}
}
// add http part
return shortURL;
}

// expandURL
// public method which returns back the original URL given the shortened url
public String expandURL(String shortURL) {
String longURL = "";
String key = shortURL.substring(domain.length() + 1);
longURL = keyMap.get(key);
return longURL;
}

// Validate URL
// not implemented, but should be implemented to check whether the given URL
// is valid or not
boolean validateURL(String url) {
return true;
}

// sanitizeURL
// This method should take care various issues with a valid url
// e.g. www.google.com,www.google.com/, http://www.google.com, // http://www.google.com/ // all the above URL should point to same shortened URL
// There could be several other cases like these.
String sanitizeURL(String url) {
if (url.substring(0, 7).equals("http://"))
url = url.substring(7);

if (url.substring(0, 8).equals("https://"))
url = url.substring(8);

if (url.charAt(url.length() - 1) == '/')
url = url.substring(0, url.length() - 1);
return url;
}

/*
* Get Key method
*/
private String getKey(String longURL) {
String key;
key = generateKey();
keyMap.put(key, longURL);
valueMap.put(longURL, key);
return key;
}

// generateKey
private String generateKey() {
String key = "";
boolean flag = true;
while (flag) {
key = "";
for (int i = 0; i <= keyLength; i++) {
key += myChars[myRand.nextInt(62)];
}
// System.out.println("Iteration: "+ counter + "Key: "+ key);
if (!keyMap.containsKey(key)) {
flag = false;
}
}
return key;
}

// test the code
public static void main(String args[]) {
URLShortener u = new URLShortener(5, "www.tinyurl.com/");
String urls[] = { "www.google.com/", "www.google.com",
"http://www.yahoo.com", "www.yahoo.com/", "www.amazon.com",
"www.amazon.com/page1.php", "www.amazon.com/page2.php",
"www.flipkart.in", "www.rediff.com", "www.techmeme.com",
"www.techcrunch.com", "www.lifehacker.com", "www.icicibank.com" };

for (int i = 0; i < urls.length; i++) {
System.out.println("URL:" + urls[i] + "\tTiny: "
+ u.shortenURL(urls[i]) + "\tExpanded: "
+ u.expandURL(u.shortenURL(urls[i])));
}
}
}