How can I append a query parameter to an existing URL?

Question

I\'d like to append key-value pair as a query parameter to an existing URL. While I could do this by checking for the existence of whether the URL has a query part or a frag

Answer 1

Use the URI class.

Create a new URI with your existing String to "break it up" to parts, and instantiate another one to assemble the modified url:

URI u = new URI("http://example.com?email=john@email.com&name=John#fragment");

// Modify the query: append your new parameter
StringBuilder sb = new StringBuilder(u.getQuery() == null ? "" : u.getQuery());
if (sb.length() > 0)
    sb.append('&');
sb.append(URLEncoder.encode("paramName", "UTF-8"));
sb.append('=');
sb.append(URLEncoder.encode("paramValue", "UTF-8"));

// Build the new url with the modified query:
URI u2 = new URI(u.getScheme(), u.getAuthority(), u.getPath(),
    sb.toString(), u.getFragment());