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

-----------------------------------------------------------------

用户登陆

用户登陆

if(request.getAttribute( "errInf ")!=null){

%>

帐号

密码

返回

---------------------------------------------------------

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);

}

}

------空指针异常解决方法--------------------------------------------------------

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

这样肯定不会空指针异常的！

out.print(result);//为什么会是null呢

可能是ResultSet resultset=db.executeQuery(query);有异常了。

------解决方法--------------------------------------------------------

if(session.getAttribute( "userId ")==null){

这句当中的'userID'你在哪setAttribute了？

------解决方法--------------------------------------------------------

DBClass db=new DBClass();

db.connect();

ResultSet resultset=db.executeQuery(query);

这个需要看看 DBClass 这个类里面的 executeQuery 方法，是怎么写的了。

有可能这个方法，把Exception给截获了，没有抛出来。

因为出错了以后，就返回NULL