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Java class for generating tiny URLs based on github.com/fogleman/ShortUrl.

jshell> ShortUrlEncoder shortUrl = ShortUrlEncoder.getInstance()
shorturl ==> ShortUrlEncoder@deadbeef

jshell> shortUrl.encodeUrl(123)
$1 ==> "9epgb"

jshell> shortUrl.decodeUrl("9epgb")
$2 ==> 123

jshell> shortUrl.encodeUrl(124)
$3 ==> "2yy2m"

jshell> shortUrl.decodeUrl("2yy2m")
$4 ==> 124

A bit-shuffling approach is used to avoid generating URLs in a consecutive, predictable order. However, the algorithm is deterministic and guarantees that no collisions will occur.

The URL alphabet is fully customizable and may contain any number of characters. By default, digits and lower-case letters are used, with some removed to avoid confusion between characters like o, O and 0. The default alphabet is shuffled and has a prime number of characters to further improve the results of the algorithm.

The block size specifies how many bits will be shuffled. The lower BLOCK_SIZE bits are reversed. Any bits higher than BLOCK_SIZE will remain as is. BLOCK_SIZE of 0 will leave all bits unaffected and the algorithm will simply be converting your integer to a different base. BLOCK_SIZE is necessary to establish an upper-bound for the bit reversal and to generate the URLs at an appropriate length.

The intended use is that incrementing, consecutive integers will be used as keys to generate the short URLs. For example, when creating a new URL, the unique integer ID assigned by a database could be used to generate the URL by using this module. Or a simple counter may be used. As long as the same integer is not used twice, the same short URL will not be generated twice.

The module supports both encoding and decoding of URLs. The min_length parameter allows you to pad the URL if you want it to be a specific length.

Use the functions in the top-level of the module to use the default encoder. Otherwise, you may create your own UrlEncoder object and use its encode_url and decode_url methods.