Question

pstmt = conn.prepareStatement(sql);中报空指针错误，sql是能运行的

----------------------------------------------------------------------------------
package Daoimpl;

import java.sql.SQLException;

import Dao.BaseDao;
import Dao.Login;

public class Loginimpl extends BaseDao implements Login{
public void Login(String a,String b) {
BaseDao base=new BaseDao();
base.openConnection();
String sql = "select * from login where username='a' and userpass='b';";
try {
pstmt = conn.prepareStatement(sql);
rs = pstmt.executeQuery();
if(!rs.next()){
System.out.print("<script>windows.location.href='/index.jsp';</script>");
}

System.out.print("<script>windows.location.href='/menu.jsp';</script>");
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally{
base.closeResource();
}
}
public void Dropservice() {
// TODO Auto-generated method stub

}
}
package Dao;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class BaseDao {
protected Connection conn = null;
protected PreparedStatement pstmt = null;
protected ResultSet rs = null;

/**
* 数据库连接方法
*/

Answer 1

你的那个conn在哪儿？

追问

在BaseDao 里面定义的 protected Connection conn = null;

追答

这不是都等于null了么，你之后又给conn赋值了么？