如何从网页内容中提取链接？

Question

I have download a web page and I want to extract all the links in that file. this links include absolutes and relatives. for example we have :

<script type="text/javascript" src="/assets/jquery-1.8.0.min.js"></script>

or

<a href="http://stackoverflow.com/" />

so after reading the file, what should I do?

Answer 1

This isn't that complicated to do, if you want to use the builtin regex system from Java. The hard bit is finding the right regex to match URLs ^[1][2] . For the sake of the answer, I'm gonna just assume you've done that, and stored that as a Pattern with syntax along the lines of this:

Pattern url = Pattern.compile("your regex here");

and some way of iterating through each line. What you'll want to do is define an ArrayList<String> :

ArrayList<String> urlsFound = new ArrayList<>();

From there, you'll have some loop to iterate through your file (assuming each line is a <? extends CharSequence> line ), and inside you'll put this:

Matcher urlMatch = url.matcher(line);
while (urlMatch.find()) urlsFound.add(urlMatch.match());

What this does is create a Matcher for your line and the URL-matching Pattern from before. Then, it loops until #find() returns false (ie, there are no more matches) and adds the match (with #group() ) to the list, urlsFound .

At the end of your loop, urlsFound will contain all the matches for all of the URLs on the page. Note that this can get quite memory-intensive if you've got a lot of text, as urlsFound will get quite big, and you'll be creating and ditching a lot of Matcher s.

^{1: I found a few good sites with a quick Google search ; the cream of the crop seem to be here and here , as far as I can tell. Your needs may vary.}

^{2: You'll need to make sure that the entire URL is captured with a single group, or this won't work at all. It can be tweaked to work if there are multiple parts, though.}