登錄頁面輸入正確的用戶名和密碼

Question

即使輸入正確的用戶名和密碼組合，登錄頁面也會顯示一條錯誤消息，指示登錄失敗。這個問題的原因是什麼？

try { 
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); 
Connection conn = DriverManager.getConnection("jdbc:odbc:mydsn","sa","password@123"); 
String sql = "select customer_id, fname, lname, email_id, phone_number from customer_details where user_name=? and password=?"; 
PreparedStatement stmt; 
ResultSet rs = stmt.executeQuery(); 
if (rs.next()) { 
session.setAttribute("customerId", rs.getString(1)); 
session.setAttribute("userName", userName); 
session.setAttribute("fName", rs.getString(2)); 
session.setAttribute("lName", rs.getString(3)); 
session.setAttribute("emailId", rs.getString(4)); 
session.setAttribute("phoneNumber", rs.getString(5)); 
conn.close(); 
%> 
<jsp:forward page="welcome.jsp" /> 
<%} else {%> 
Sorry! You have entered an invalid username or password. Please try again. 
<%} 
conn.close(); 
} catch (SQLException e) { 
e.printStackTrace(); 
} 
} 

Answer 1

這是因爲

PreparedStatement stmt; 
ResultSet rs = stmt.executeQuery(); 

stmt是你的代碼null

幾點建議：

• Avoid java code in jsp
在 servlet
• 處理異常
• 編寫Java代碼正確