open and save web page selenium java

In Selenium you can do this:

SafariDriver driver = new SafariDriver(); //you can use any drivers like Chrome,FireFox
driver.get("your link");
String pageSource = driver.getPageSource(); //now you have the page source
//you can save the pageSource to the file or do what ever you want. 

Look at the getPageSource docs here.

If you want to get data from the specific tags, like say for example body, then you can do this:

String pageSource=driver.findElement(By.tagName("body")).getText();

Keep in mind that Selenium is meant for web page automation, so for interacting with the pages automatically. If only the source is really what you need, you can use a JSoup a really solid Java Html parser, in two lines of code, you should have your source

     try {
            Document doc = Jsoup.connect("http://www.ncbi.nlm.nih.gov/nuccore/NM_007002").userAgent("Mozilla/5.0").timeout(30000).get();
            System.out.println(doc.toString());
        } catch (IOException e) {
            e.printStackTrace();
        }