Java: How to easily check if a URL was already shortened?

问题

If I have a general url (not restricted to twitter or google) like this:

http://t.co/y4o14bI

is there an easy way to check if this url is shortened?

In the above case, I as a human can of course see that it was shortend, but is there an automatic and elegant way?

回答1:

You could do a request to the URL, look if you get redirected and if so, assume it's a shortening service. For this you'd have to read the HTTP status codes.

On the other hand, you could whitelist some URL shortening services (t.co, bit.ly, and so on) and assume all links to those domains are shortened.

Drawback of the first method is that it isn't certain, some sites use redirects internally. The drawback of the second method is that you'd have to keep adding shortening services, although only a few are used widely.

回答2:

One signal may be to request the URL and see if it results in a redirect to another domain. However, without a good definition of what "shortened" means, there is no generic way.

回答3:

if you know all the domains that can be used to shorten your URLs, check if it is contained :

String[] domains = {"bit.ly", "t.co"...};
for(String domain : domains){
  if(url.startsWith("http://" + domain)){
    return true;
  }
}
return false;

回答4:

You can't: You will have to work by assumption.

Assumption:

Does www exist in url.
Does the server name end with a valid domain (e.g. com, edu, etc.) or does it has co.xx where xx is a valid country or organization code.

And you can add more assumption based on other url shortening links.

回答5:

You can't.

You can only check if you list a couple of shorteners and check if the url starts with it.

You can also try checking whether the url is shorter than a given length (and contains path/query string), but some shorteners (tinyurl for example) may have longer urls than normal sites (aol.com)

I would prefer the list of known shorteners.

回答6:

Here's what you could do in Java, groovy and the like.

Get the url you want to test;
Open the url with HttpURLConnection
Check the response code
if it is a valid code, 200 for example, the you can retrieve the url string in long form from the connection object if it was shortened or back in its original form if it wasn't.

We all love to see some code don't we. Its crude, but hey!

String addr = "http://t.co/y4o14bI";
URL url = new URL(addr);

HttpURLConnection connection = (HttpURLConnection) url.openConnection();

if (connection.getResponseCode() == 200) {
    String longUrl = connection.url;
    System.out.println(longUrl);
} else {
    // You decide what you want to do here!
}

回答7:

Actually, you as a human, can't. The only way you know that it's shortened is that it's a t.co domain. The y4o14bI could be an CMS identifier for all you know.

The best way would be to use a list of known shortener urls, and lookup against that.

And even then you would have problems. I use bit.ly with a personal domain, wtn.gd

So http://wtn.gd/random would also be a shortened URL.

You could maybe do a HTTP HEAD-request, and check for a 301/302 ?

回答8:

If you request an URL like this, your HttpCLient should receive a HTTP Redirect instead of a HTML page. This wouldn't be an evidence but at least a hint.

回答9:

Evaluate the URL and look for some clues:

the Path meets certain criteria
- only has one step (i.e. not multiple slashes)
- does not end with filename extensions
- not longer than X characters (would need to evaluate various URL shortening services and adjust the upper bounds for the max token length)
HttpUrlConnection returns a redirect responseCode (i.e. 301, 302)

来源：https://stackoverflow.com/questions/8151163/java-how-to-easily-check-if-a-url-was-already-shortened

标签

java

url-shortener