ciao a tutti
ho fatto la seguente pagina jsp che fa da interfaccia con una servlet:
codice:
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<%@page import="it.netmon.OutputBean"%><html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>

<form method="post" name="myForm" action="/NetMon/AdminServlet">

	<table>
		<tr>
			<td>Tipo Richiesta</td>
			<td>
				<select name="opRich">
					<option value="1" <%=request.getParameter("opRich").equals("1")?"selected":"" %>>Lista Client[1]</option>
					<option value="2" <%=request.getParameter("opRich").equals("2")?"selected":"" %>>Info pc [2]</option>
					<option value="3" <%=request.getParameter("opRich").equals("3")?"selected":"" %>>Test TCP [3]</option>
					<option value="4" <%=request.getParameter("opRich").equals("4")?"selected":"" %>>Test UDP [4]</option>
					<option value="5" <%=request.getParameter("opRich").equals("5")?"selected":"" %>>Carico Centralizzato [5]</option>
					<option value="6" <%=request.getParameter("opRich").equals("6")?"selected":"" %>>Carico anello[6]</option>
					<option value="7" <%=request.getParameter("opRich").equals("7")?"selected":"" %>>Carico anello server[7]</option>	
				</select>
			</td>
		</tr>
		<tr>
			<td><input type="submit" name="Invio" value="Invio" /></td>
			<td><input type="submit" onclick="document.myForm.action='/NetMon/index.jsp'"  name="Reset" value="Reset"/></td>
		</tr>
	</table>
</form>
<% 	
	if (request.getParameter("Reset") != null) {
		session.setAttribute("outputBean",null);
	}
	
	if (request.getSession().getAttribute("outputBean") != null) {
		OutputBean ob = (OutputBean)request.getSession().getAttribute("outputBean");
		if (request.getParameter("opRich").equals("1")) {/* stampa solo le opzioni 1*/}
		for(int a = 0;a < ob.getNomeClient().size();a++) { %>
			Nome Client: <%= ob.getNomeClient().elementAt(a)%> attraverso la porta: <%= ob.getPortClient().elementAt(a)%>
<%		}	%>
		

<%		if (ob.getNote() != null) {%>
			Si è verificato un'errore: <%= ob.getNote()%>
	<%	}
	}

%>

</body>
</html>
ma quando la eseguo mi da il seguente errore:

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

org.apache.jasper.JasperException: java.lang.NullPointerException
org.apache.jasper.servlet.JspServletWrapper.handle JspException(JspServletWrapper.java:491)
org.apache.jasper.servlet.JspServletWrapper.servic e(JspServletWrapper.java:419)
org.apache.jasper.servlet.JspServlet.serviceJspFil e(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspSe rvlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet .java:717)


root cause

java.lang.NullPointerException
org.apache.jsp.index_jsp._jspService(index_jsp.jav a:72)
org.apache.jasper.runtime.HttpJspBase.service(Http JspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet .java:717)
org.apache.jasper.servlet.JspServletWrapper.servic e(JspServletWrapper.java:377)
org.apache.jasper.servlet.JspServlet.serviceJspFil e(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspSe rvlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet .java:717)



non riesco a capire a cosa sia dovuto...voi avete in mente qualcosa??