java.lang.NumberFormatException: null with Integer.Parseint(

*当我尝试在服务器上运行我的 JSP 时，我遇到了这个问题...... servlet 是：

@WebServlet({"/Registrazione" , "/Registrazione.jsp"})
public class Registrazione extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public Registrazione() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
ClienteDAO d=new ClienteDAO();
String idCliente=request.getParameter("userid");
String nome=request.getParameter("nome");
String cognome=request.getParameter("cog");
String partitaIva=request.getParameter("piva");
String codiceFiscale=request.getParameter("cf");
String email=request.getParameter("eml");
String fidelity=request.getParameter("fid");
String via=request.getParameter("via");
String numerocivico = request.getParameter("nciv");
String password=request.getParameter("pw");

Cliente cliente=new Cliente(Integer.parseInt(idCliente),nome,cognome,partitaIva,codiceFiscale, email,Integer.parseInt(fidelity),via,Integer.parseInt(numerocivico),password);
d.salvaCliente(cliente);
response.getWriter().append("utente registrato").append(request.getContextPath());
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}

JSP 是

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Registrazione</title>
</head>
<body>
<form action="/Registrazione" name="FormRegistrazione" method="get" >
Username:<input type="text" name="userid" value="">
<br>
Nome:<input type="text" name="nome" value="">
<br>
Cognome:<input type="text" name="cog" value="">
<br>
PIVA:<input type="text" name="piva" value="">
<br>
CF:<input type="text" name="cf" value="">
<br>
email:<input type="text" name="eml" value="">
<br>
fidelity:<input type="text" name="fid" value="">
<br>
via:<input type="text" name="via" value="">
<br>
civico:<input type="text" name="nciv" value="">
<br>
password:<input type="text" name="pw" value="">
<br>
<input type="submit" value="invia">
</form>
</body>
</html>
}*

但是当我尝试从服务器运行 JSP 时，我看到这个：

HTTP Status 500 – Internal Server Error

Type Exception Report
Message null
Description The server encountered an unexpected condition that prevented it from fulfilling the request.
Exception
java.lang.NumberFormatException: null
java.lang.Integer.parseInt(Unknown Source)
java.lang.Integer.parseInt(Unknown Source)
it.unirc.twd.BuyeDrink.servlet.NuovoCliente.doGet(NuovoCliente.java:37)
javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)

Note The full stack trace of the root cause is available in the server logs.

我有一个类似的servlet，它运行得很好，但在表单中也有"值。所以我无法理解整数解析Int 的问题......怎么了？

String x = null;    
Integer.parseInt(x) // will rase the exception

抛出： NumberFormatException - 如果字符串不包含可解析的整数。

在此处查看甲骨文文档

如果我运行这个servlet：

@WebServlet({ "/AggiungiStudente", "/AggiungiStudente.jsp" })
public class AggiungiStudente extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public AggiungiStudente() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
StudenteDAO dao = new StudenteDAO();
String matricola = request.getParameter("matricola");
String nome = request.getParameter("nome");
String cognome = request.getParameter("cognome");
String password = request.getParameter("password");
String idcdl = request.getParameter("idcdl");
Studente s = new Studente(Integer.parseInt(matricola),nome,cognome,password,Integer.parseInt(idcdl));
dao.salvaStudente(s);       
response.sendRedirect("/VisualizzaStudente");
response.getWriter().append("Utente aggiunto").append(request.getContextPath());
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}

}

有了这个JSP

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<form method="get" action="/AggiungiStudente">
<table style="height: 400px; width: 598px;border: 1">
<tbody>
<tr>
<td style="width: 118px;">&nbsp;Matricola:</td>
<td style="width: 473px;">&nbsp;<input type="text" name="matricola" value=""></td>
</tr>
<tr>
<td style="width: 118px;">&nbsp;Nome:&nbsp;</td>
<td style="width: 473px;">&nbsp;<input type="text" name="nome" value=""></td>
</tr>
<tr>
<td style="width: 118px;">&nbsp;Cognome:</td>
<td style="width: 473px;">&nbsp;<input type="text" name="cognome" value=""></td>
</tr>
<tr>
<td style="width: 118px;">&nbsp;Password:</td>
<td style="width: 473px;">&nbsp;<input type="password" name="password" value=""></td>
</tr>
<tr>
<td style="width: 118px;">IdCdl:</td>
<td style="width: 473px;">&nbsp;<input type="text" name="idcdl" value=""></td>
</tr>
</tbody>
</table>

<input type="submit" value="Aggiungi">
</form>         
</body>
</html>

当我单击"Aggiungi"时，我在表单中插入的值将插入到甲骨文的数据库中......我想在另一个数据库中做同样的事情

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