空指针异常
在提交的servlet里出现异常
ACCESS数据库
id自动获取
password文本类型
测试id,password值能传递过来
不明白为什么
String query="select * from customer where password="+pwd; //这样是空指针异常
String query="select * from customer where id='"+id+"' and password='"+pwd+"'";//这样也是空指针异常
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<%@page contentType="text/html;charset=gb2312" language="java" import="java.sql.*" errorPage=""%>
<html>
<head><title>用户登陆</title></head>
<body>
用户登陆
<form method="post" action="/jsp/UserLogin">
<%
if(request.getAttribute("errInf")!=null){
%>
<%=(String)request.getAttribute("errInf")%>
<%}%>
帐号<input type="text" name="id">
密码<input type="password" name="password"></p>
<input type="submit" value="提交">
<a href="/jsp/changePassword.jsp">返回</a>
</body>
</html>
---------------------------------------------------------
UserLogin
import java.io.*;
import java.sql.*;
import javax.servlet.*;
import javax.servlet.http.*;
import bean.DBClass;
import bean.StrClass;
import bean.UserInf;
public class UserLogin extends HttpServlet{
public void doPost(HttpServletRequest request,HttpServletResponse response)throws ServletException,IOException{
HttpSession session=request.getSession();
String toJsp="/hasLogin.jsp";
if(session.getAttribute("userId")==null){
String id=request.getParameter("id");
String pwd=request.getParameter("pwd"); //String query="select * from customer where id="+id; 这样就可以正常登陆
//String query="select * from customer where password="+pwd; 这样是空指针异常
String query="select * from customer where id='"+id+"' and password='"+pwd+"'";//这样也是空指针异常
DBClass db=new DBClass();
db.connect();
ResultSet resultset=db.executeQuery(query);
try{
if(resultset.next()){
session.setAttribute("userid",id);
toJsp="/loginSuccess.jsp";
}
else{
toJsp="/userLogin.jsp";
request.setAttribute("errIn","*密码与帐号不匹配");
}
}
catch(SQLException sqle){
System.err.println("Erro width connection:"+sqle);
}
db.closeConnection();
}
RequestDispatcher dispatcher=request.getRequestDispatcher(toJsp);
dispatcher.forward(request,response);
}
}