Java library to extract links such as URLs and email addresses from plain text. Fast, small and smart about recognizing where links end.

Inspired by Rinku. Similar to it, regular expressions are not used. Instead, the input text is parsed in one pass with limited backtracking.

This library requires Java 7. It works on Android (minimum API level 15). It has no external dependencies.

Maven coordinates (see here for other build systems):

<dependency>
    <groupId>org.nibor.autolink</groupId>
    <artifactId>autolink</artifactId>
    <version>0.6.0</version>
</dependency>

Extract links:

import org.nibor.autolink.*;

String input = "wow, so example: http://test.com";
LinkExtractor linkExtractor = LinkExtractor.builder()
        .linkTypes(EnumSet.of(LinkType.URL, LinkType.WWW, LinkType.EMAIL))
        .build();
Iterable<LinkSpan> links = linkExtractor.extractLinks(input);
LinkSpan link = links.iterator().next();
link.getType();        // LinkType.URL
link.getBeginIndex();  // 17
link.getEndIndex();    // 32
input.substring(link.getBeginIndex(), link.getEndIndex());  // "http://test.com"

Note that by default all supported types of links are extracted. If you're only interested in specific types, narrow it down using the linkTypes method.

There's also a static method to replace links found in the text. Here's an example of using that for wrapping URLs in an <a> tag. Note that it doesn't handle escaping at all:

import org.nibor.autolink.*;

String input = "wow http://test.com such linked";
LinkExtractor linkExtractor = LinkExtractor.builder()
        .linkTypes(EnumSet.of(LinkType.URL)) // limit to URLs
        .build();
Iterable<LinkSpan> links = linkExtractor.extractLinks(input);
String result = Autolink.renderLinks(input, links, (link, text, sb) -> {
    sb.append("<a href=\"");
    sb.append(text, link.getBeginIndex(), link.getEndIndex());
    sb.append("\">");
    sb.append(text, link.getBeginIndex(), link.getEndIndex());
    sb.append("</a>");
});
result;  // "wow <a href=\"http://test.com\">http://test.com</a> such linked"

Extracts URLs of the form scheme://example with any scheme. URIs such as example:test are not matched (may be added as an option in the future). If only certain schemes should be allowed, the result can be filtered.

Includes heuristics for not including trailing delimiters such as punctuation and unbalanced parentheses, see examples below.

Supports internationalized domain names (IDN). Note that they are not validated and as a result, invalid URLs may be matched.

Example input and linked result:

• http://example.com. → http://example.com.
• http://example.com, → http://example.com,
• (http://example.com) → (http://example.com)
• (... (see http://example.com)) → (... (see http://example.com))
• https://en.wikipedia.org/wiki/Link_(The_Legend_of_Zelda) → https://en.wikipedia.org/wiki/Link_(The_Legend_of_Zelda)
• http://üñîçøðé.com/ → http://üñîçøðé.com/

Use LinkType.URL for this, and see test cases here.

Extract links like www.example.com. They need to start with www. but don't need a scheme://. For detecting the end of the link, the same heuristics apply as for URLs.

Examples:

• www.example.com. → www.example.com.
• (www.example.com) → (www.example.com)
• [..] link:www.example.com [..] → [..] link:www.example.com [..]

Not supported:

• Uppercase www's, e.g. WWW.example.com and wWw.example.com
• Too many or too few w's, e.g. wwww.example.com

The domain must have at least 3 parts, so www.com is not valid, but www.something.co.uk is.

Use LinkType.WWW for this, and see test cases here.

Extracts emails such as [email protected]. Matches international email addresses, but doesn't verify the domain name (may match too much).

Examples:

• [email protected] → [email protected]
• [email protected]. → [email protected].
• [email protected], → [email protected],
• üñîçøðé@üñîçøðé.com → üñîçøðé@üñîçøðé.com

Not supported:

• Quoted local parts, e.g. "this is sparta"@example.com
• Address literals, e.g. foo@[127.0.0.1]

Note that the domain must have at least one dot (e.g. foo@com isn't matched), unless the emailDomainMustHaveDot option is disabled.

Use LinkType.EMAIL for this, and see test cases here.

Extract Twitter/Facebook/Instagram Hashtags such as #photooftheday. Hashtags need to start with #. In general hashtags do not contain special characters other than _. Also hashtags cannot be all numeric. For example, #123 is not a valid hashtag.

Examples:

• #photooftheday → #photooftheday
• #photo_of_the_day. → #photo_of_the_day.

You can configure the allowed special characters in the hashtag. For example if you want to extract the hashtags containing both _ and '-', then you can configure your builder as shown:

import org.nibor.autolink.*;

String input = "#photo-of-the-day";
Set<Character> allowedSpecialChars = new HashSet<Character>() {{
    add('_');
    add('-');
}};
LinkExtractor linkExtractor = LinkExtractor.builder()
        .linkTypes(EnumSet.of(LinkType.URL, LinkType.HASHTAG))
        .allowedHashtagSpecialChars(allowedSpecialChars)
        .build();
Iterable<LinkSpan> links = linkExtractor.extractLinks(input);
String result = Autolink.renderLinks(input, links, new LinkRenderer() {
    @Override
    public void render(LinkSpan link, CharSequence text, StringBuilder sb) {
        System.out.println("Link: " + link);
        sb.append("<a href=\"https://api.twitter.com/1.1/search/tweets.json?q=");
        sb.append(text, link.getBeginIndex(), link.getEndIndex());
        sb.append("\">");
        sb.append(text, link.getBeginIndex(), link.getEndIndex());
        sb.append("</a>");
    }
});
System.out.println(result); // <a href="https://api.twitter.com/1.1/search/tweets.json?q=#photo-of-the-day">#photo-of-the-day</a>

see test cases here.

Pull requests, issues and comments welcome ☺. For pull requests:

• Add tests for new features and bug fixes
• Follow the existing style (always use braces, 4 space indent)
• Separate unrelated changes into multiple pull requests

Copyright (c) 2015-2016 Robin Stocker and others, see Git history

MIT licensed, see LICENSE file.