servlet中获得tomcat项目根目录的绝对路径

public class CreateXmlAction extends HttpServlet {

private ServletConfig config;
public void init(ServletConfig config) throws ServletException {
this.config = config;
}

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String  filePath = config.getServletContext().getRealPath("/");
}
}