JSP页面上获取servlet里面值的问题

servlet中：List accounts = new ArrayList();
System.out.print("!!!"+accounts.size());//能正确输出大小

JSP中： List VistSites=(List)request.getAttribute("accounts");

System.out.print( VistSites.size()); //出错
下面是
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:521)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:430)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet.java:723)

root cause
java.lang.NullPointerException
org.apache.jsp.Search_jsp._jspService(Search_jsp.java:179)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:723)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:388)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet.java:723)

JSP页面上获取servlet 的传值：
在Servlet中使用request.setAttribute("name",value);
RequestDispatcher rd=request.getRequestDispatcher("跳转的页面");
rd.forward(request,response);
在JSP页面中取得值写法：<%=request.setAttribute("name")%>

servlet中用request.getparameter("参数名")取得值,前台你js里面把需要传的i变量,加入到访问servlet的url后面就行