Question

求大神帮我，pstmt = conn.prepareStatement(sql);空指针，sql是能够运行的

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

pstmt = conn.prepareStatement(sql);这句话出现空指针，那肯定说明conn是空的，把BaseDao里的代码全贴出来

Answer 2

直接设置if(conn!=null){
pstmt = conn.prepareStatement(sql)
............代码
}