Question

In Java I have:

String params = "depCity=PAR&roomType=D&depCity=NYC";

I want to get values of depCity parameters (PAR,NYC).

So I created regex:

String regex = "depCity=([^&]+)";
Pattern p = Pattern.compile(regex);
Matcher m = p.matcher(params);

m.find() is returning false. m.groups() is returning IllegalArgumentException.

What am I doing wrong?

Answer 1

It doesn’t have to be regex. Since I think there’s no standard method to handle this thing, I’m using something that I copied from somewhere (and perhaps modified a bit):

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, when you call it, you will get all parameters and their values. The method handles multi-valued params, hence the List<String> rather than String, and in your case you’ll need to get the first list element.