Question

Sometimes you need to construct a full URL to your web app context inside a servlet/JSP/whatever based on HttpServletRequest.
Something like http://server.name:8080/context/. Servlet API doesn’t have a single method to achieve this.

The straightforward approach is to append all URL components to a StringBuffer, like

ctxUrl = sb.append(req.getScheme()).append("://")
.append(req.getgetServerName()).append(":")
.append(req.getServerPort()) etc

I wonder if there’s anything wrong with this alternative (which is 10 times faster):

ctxUrl = req.getRequestURL();
ctxUrl = ctxUrl.substring(0, ctxUrl.lastIndexOf("/")));

Will two above methods always produce the same result?

Answer 1

It’s called the "base URL" (the one you could use in HTML <base> tag). You can obtain it as follows:

StringBuffer url = req.getRequestURL();
String uri = req.getRequestURI();
String ctx = req.getContextPath();
String base = url.substring(0, url.length() - uri.length() + ctx.length()) + "/";

Your ctxUrl.substring(0, ctxUrl.lastIndexOf("/"))); approach will fail on URLs with multiple folders like http://server.name:8080/context/folder1/folder2/folder3.

See also:

• How to use relative paths without including the context root name? (for a JSP answer)
• How get the base URL? (for a JSF answer)