Java Web Crawler Libraries

This is How your program 'visit' or 'connect' to web pages.

    URL url;
    InputStream is = null;
    DataInputStream dis;
    String line;

    try {
        url = new URL("http://stackoverflow.com/");
        is = url.openStream();  // throws an IOException
        dis = new DataInputStream(new BufferedInputStream(is));

        while ((line = dis.readLine()) != null) {
            System.out.println(line);
        }
    } catch (MalformedURLException mue) {
         mue.printStackTrace();
    } catch (IOException ioe) {
         ioe.printStackTrace();
    } finally {
        try {
            is.close();
        } catch (IOException ioe) {
            // nothing to see here
        }
    }

This will download source of html page.

For HTML parsing see this

Also take a look at jSpider and jsoup

Crawler4j is the best solution for you,

Crawler4j is an open source Java crawler which provides a simple interface for crawling the Web. You can setup a multi-threaded web crawler in 5 minutes!

Also visit. for more java based web crawler tools and brief explanation for each.

Right now there is a inclusion of many java based HTML parser that support visiting and parsing the HTML pages.

• Jsoup
• Jaunt API
• HtmlCleaner
• JTidy
• NekoHTML
• TagSoup

Here's the complete list of HTML parser with basic comparison.