protected void doPost(
		HttpServletRequest request,
		HttpServletResponse response)
		throws ServletException, IOException {
        //service name,example for packagename.ServiceName
        String serviceName = request.getParameter(Constant.SERVICE);
		if (serviceName == null)
			throw new ServletException("There isn't service parameter![?service=]");
		String targetName = request.getParameter(Constant.TARGET);
        //the targeted file name,example for /fileName.jsp
		if (targetName == null)
			throw new ServletException("There isn't target parameter![?target=]");
		ServletContext servletcontext = getServletContext();
		try {
            //TODO:hashmap to reduce the generated instance? 
			Class serviceClass = Class.forName(serviceName);
			Service service = (Service) serviceClass.newInstance();
			service.execute(request, response, servletcontext);
		} catch (ClassNotFoundException classnotfoundexception) {
			throw new ServletException(classnotfoundexception.getMessage());
		} catch (IllegalAccessException illegalaccessexception) {
			throw new ServletException(illegalaccessexception.getMessage());
		} catch (Exception exception) {
			throw new ServletException(exception.getMessage());
		}
		forward(request, response, targetName);
	}

public interface Service {
	public abstract void execute(
		HttpServletRequest httpservletrequest,
		HttpServletResponse httpservletresponse,
		ServletContext servletcontext)
		throws Exception;
}

public class StartService implements Service {

	public void execute(
		HttpServletRequest httpservletrequest,
		HttpServletResponse httpservletresponse,
		ServletContext servletcontext)
		throws Exception {
        //test data
		List userList = new ArrayList();
        httpservletrequest.setAttribute("USERNAME", "TestUser");
        httpservletrequest.setAttribute("USERLIST", userList);
	}

}

<%
String userName=(String)request.getAttribute("USERNAME");
List userList=(List)request.getAttribute("USERLIST");
%>

//TODO:hashmap to reduce the generated instance? 
Class serviceClass = Class.forName(serviceName);
Service service = (Service) serviceClass.newInstance();
service.execute(request, response, servletcontext);