Simplest way to strip an int out of a URL in Java?

I have a String containing a URL. I want to get just one piece of data out of it: an int th开发者_如何学编程at should be showing up in the query string.

So if the url is:

http://domain.tld/page.html?iVar=123

I want to get "123" into an int.

What's the most elegant way you know to do this?

You could try matching just that parameter in the URL string:

public static Integer getIVarParamValue(String urlStr) {
  Pattern p = Pattern.compile("iVar=(\\d+)");
  Matcher m = p.matcher(urlStr);
  if (m.find()) {
    return Integer.parseInt(m.group(1));
  }
  return null;
}

It seems you want to obtain get parameters and parse them. I have this method here (got it from somewhere on SO, I guess):

public static Map<String, List<String>> getQueryParams(String url) {
    try {
        Map<String, List<String>> params = new HashMap<String, List<String>>();
        String[] urlParts = url.split("\\?");
        if (urlParts.length > 1) {
            String query = urlParts[1];
            for (String param : query.split("&")) {
                String[] pair = param.split("=");
                String key = URLDecoder.decode(pair[0], "UTF-8");
                String value = "";
                if (pair.length > 1) {
                    value = URLDecoder.decode(pair[1], "UTF-8");
                }

                List<String> values = params.get(key);
                if (values == null) {
                    values = new ArrayList<String>();
                    params.put(key, values);
                }
                values.add(value);
            }
        }

        return params;
    } catch (UnsupportedEncodingException ex) {
        throw new AssertionError(ex);
    }
}

So:

String var = WebUtils.getQueryParams(url).get("iVar");
int intVar = Integer.parseInt(var);

You can use the URL class. i.e.:

URL myUrl = new URL("http://domain.tld/page.html?iVar=123");

String query = myUrl.getQuery(); //this will return iVar=123
//at this point you can either parse it manually (i.e. use some of the regexp in the other suggestions, or use something like:
String[] parts = query.split();
String variable = parts[0];
String value = parts[1];

This will work only for this case though and won't work if you have additional params or no params. There are a number of solution that will split it into a param map online, you can see some here.

If it's really as simple as you describe: There is only 1 int in your URL and all you want is that int, I'd go for a regular expression. If it is actually more complicated see the other answers.

    Pattern p = Pattern.compile("[0-9]+");
    Matcher m = p.matcher("http://domain.tld/page.html?iVar=123");
    if (m.find())
        System.out.println(m.group());

This also could do the work :

public static int getIntParam(HttpServletRequest request, String name, int defaultValue) {
    String value = request.getParameter(name);
    try {
        if (value != null) {
            return Integer.valueOf(value);
        }
    } catch (NumberFormatException e) {
    }
    return defaultValue;
}

Hope it helps!

If the query string part of the URL is always the same (so if it was always iVar) you could use urlAsString.indexOf("iVar=") to find iVar= and then knowing the number is after that, extract the number. That is admittedly not the least brittle approach.

But if you're looking for all the query strings then Bozho's answer is much better.