This is a simple encode() and decode() function.
Note that we haven't created the MD5 hashing approach here as this only deals with the concept.
Step:
encode()
- save the long url in db, get a unique long id from db for that url
- pass that long id to the
encode(id)function - so for a long value we keep diving it by 62 and pick a value from the allowed chars array and keep adding it
- make sure to reverse the created string
private static final String allowedString = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
private final char[] allowedCharacters = allowedString.toCharArray();
private final int base = allowedCharacters.length; // 62
public String encode(long input){
var encodedString = new StringBuilder();
if(input == 0) {
return String.valueOf(allowedCharacters[0]);
}
while (input > 0) {
encodedString.append(allowedCharacters[(int) (input % base)]);
input = input / base;
}
return encodedString.reverse().toString();
}
decode()
- send the last part of the url - which is the encoded string
- convert the string to array
- from first value we pick index of value and multiply it with
62^remaining characters - the number is the decoded id
public long decode(String input) {
var characters = input.toCharArray();
var length = characters.length;
var decoded = 0;
//counter is used to avoid reversing input string
var counter = 1;
for (char character : characters) {
decoded += allowedString.indexOf(character) * Math.pow(base, length - counter);
counter++;
}
return decoded;
}
So if we have the decoded url, we could simply return it as a header location - with the response code of 302 (FOUND)
@GetMapping(value = "{shortUrl}")
public ResponseEntity<Void> getAndRedirect(@PathVariable String shortUrl) {
var url = urlService.getOriginalUrl(shortUrl);
return ResponseEntity.status(HttpStatus.FOUND)
.location(URI.create(url))
.build();
}
}
The problems:
- we are relaying on a single db table id to generate the ids
- not scalable, how do we handle a fixed size return url
- how do we allow customised URLs
- can we reuse a short-url which is removed/expired?
I will be working on a more distributed solutions in coming posts, Thanks you for reaching here.
Here's a 🍪
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