Use a HTML parser instead of regex. This is dead simple with Jsoup.

public static String html2text(String html) {
    return Jsoup.parse(html).text();
}

Jsoup also supports removing HTML tags against a customizable whitelist, which is very useful if you want to allow only e.g. <b>, <i> and <u>.

See also:

• RegEx match open tags except XHTML self-contained tags
• What are the pros and cons of the leading Java HTML parsers?
• XSS prevention in JSP/Servlet web application