一、user java class

    test pass under Window platform

    public class Util {
         /**
          * Get web application root real path

          * 
          */
         public static String getWebAppRootPath() {
            String result = Util.class.getResource("Util.class").toString();
            System.out.print(result);
            int index = result.indexOf("WEB-INF");
            if (index == -1) {
               index = result.indexOf("bin");
            }
            result = result.substring(0, index);
            if (result.startsWith("zip")) {     //  class at *.war ,"zip:D:/ ..."
               result = result.substring(10);
            } else if (result.startsWith("file")) {    //  class at classes, "file:/f:/ ..."   
               result = result.substring(6);
            }else if(result.startsWith("jar")){        // class at *.jar, "jar:file:/F:/ ..."
               result = result.substring(4);
            }
            if (result.endsWith("/"))  result = result.substring(0, result.length() - 1);
               result = result.replace("%20", " "); 

               return result;
         }

    }
二、user Web application object

   JSP：
      <%= application.getRealPath("/") %>
   Servlet:
      this.getFilterConfig().getServletContext().getRealPath("/");//invoke at servlet filter
   Struts2:
      org.apache.struts2.ServletActionContext.getServletContext().getRealPath("/");