Regex to strip HTML tags

Since you asked, here's a quick and dirty solution:

String stripped = input.replaceAll("<[^>]*>", "");

(Ideone.com demo)

Using regexps to deal with HTML is a pretty bad idea though. The above hack won't deal with stuff like

• <tag attribute=">">Hello</tag>
• <script>if (a < b) alert('Hello>');</script>

etc.

A better approach would be to use for instance Jsoup. To remove all tags from a string, you can for instance do Jsoup.parse(html).text().

Use a HTML parser. Here's a Jsoup example.

String input = "<font size=\"5\"><p>some text</p>\n<p>another text</p></font>";
String stripped = Jsoup.parse(input).text();
System.out.println(stripped);

Result:

some text another text

Or if you want to preserve newlines:

String input = "<font size=\"5\"><p>some text</p>\n<p>another text</p></font>";
for (String line : input.split("\n")) {
    String stripped = Jsoup.parse(line).text();
    System.out.println(stripped);
}

Result:

some text
another text

Jsoup offers more advantages as well. You could easily extract specific parts of the HTML document using the select() method which accepts jQuery-like CSS selectors. It only requires the document to be semantically well-formed. The presence of the since 1998 deprecated <font> tag is already not a very good indication, but if you know the HTML structure in depth detail beforehand, it'll still be doable.

See also:

• Pros and cons of leading HTML parsers in Java

Starting from aioobe's code, I tried something more daring:

String input = "<font size=\"5\"><p>some text</p>\n<p>another text</p></font>";
String stripped = input.replaceAll("</?(font|p){1}.*?/?>", "");
System.out.println(stripped);

The code to strip every HTML tag would look like this:

public class HtmlSanitizer {

    private static String pattern;

    private final static String [] tagsTab = {"!doctype","a","abbr","acronym","address","applet","area","article","aside","audio","b","base","basefont","bdi","bdo","bgsound","big","blink","blockquote","body","br","button","canvas","caption","center","cite","code","col","colgroup","content","data","datalist","dd","decorator","del","details","dfn","dir","div","dl","dt","element","em","embed","fieldset","figcaption","figure","font","footer","form","frame","frameset","h1","h2","h3","h4","h5","h6","head","header","hgroup","hr","html","i","iframe","img","input","ins","isindex","kbd","keygen","label","legend","li","link","listing","main","map","mark","marquee","menu","menuitem","meta","meter","nav","nobr","noframes","noscript","object","ol","optgroup","option","output","p","param","plaintext","pre","progress","q","rp","rt","ruby","s","samp","script","section","select","shadow","small","source","spacer","span","strike","strong","style","sub","summary","sup","table","tbody","td","template","textarea","tfoot","th","thead","time","title","tr","track","tt","u","ul","var","video","wbr","xmp"};

    static {
        StringBuffer tags = new StringBuffer();
        for (int i=0;i<tagsTab.length;i++) {
            tags.append(tagsTab[i].toLowerCase()).append('|').append(tagsTab[i].toUpperCase());
            if (i<tagsTab.length-1) {
                tags.append('|');
            }
        }
        pattern = "</?("+tags.toString()+"){1}.*?/?>";
    }

    public static String sanitize(String input) {
        return input.replaceAll(pattern, "");
    }

    public final static void main(String[] args) {
        System.out.println(HtmlSanitizer.pattern);

        System.out.println(HtmlSanitizer.sanitize("<font size=\"5\"><p>some text</p><br/> <p>another text</p></font>"));
    }

}

I wrote this in order to be Java 1.4 compliant, for some sad reasons, so feel free to use for each and StringBuilder...

Advantages:

• You can generate lists of tags you want to strip, which means you can keep those you want
• You avoid stripping stuff that isn't an HTML tag
• You keep the whitespaces

Drawbacks:

• You have to list all HTML tags you want to strip from your string. Which can be a lot, for example if you want to strip everything.

If you see any other drawbacks, I would really be glad to know them.

If you use Jericho, then you just have to use something like this:

public String extractAllText(String htmlText){
    Source source = new Source(htmlText);
    return source.getTextExtractor().toString();
}

Of course you can do the same even with an Element:

for (Element link : links) {
  System.out.println(link.getTextExtractor().toString());
}