註冊驗證無效java

Question

String email = email_register_txt.getText(); 
    String username = username_register_txt.getText(); 

    Statement stmt = db_connection.connect().createStatement(); 

    String sql = "SELECT * FROM user_profile WHERE username=' "+username+" ' OR user_email=' "+email+" ' "; 

    res = stmt.executeQuery(sql); 

    if(res.next()) { 

     if(res.getString("username").equalsIgnoreCase(username)) { 
          JOptionPane.showMessageDialog(registerPanel, "The username has already been already registered!"); 

     } else if (res.getString("user_email").equalsIgnoreCase(email)) { 
          JOptionPane.showMessageDialog(registerPanel, "This email address has already been already registered!"); 
    } 

} else { ... 

當我輸入已插入數據庫的用戶名/電子郵件時，出現這些錯誤消息。 我的註冊工作，但我認爲驗證部分可能會錯過什麼？

Answer 1

你顯然不會顯示所有相關的代碼，或者你只是忽略了將所需的代碼放入應該使其工作的方法中。

A ResultSet基本上是您的查詢的結果集合，您需要遍歷該結果以訪問該查詢的所有結果。 A 而循環被廣泛用作遍歷結果集對象中包含的所有結果的手段。我在代碼中看不到你已經聲明瞭一個ResultSet對象，但你正在嘗試使用它。也許嘗試是這樣的：

String email = email_register_txt.getText(); 
String username = username_register_txt.getText(); 

try { 
    Connection conn = DriverManager.getConnection("...your jdbc connection string..."); 
    conn.setAutoCommit(false); 

    String sql = "SELECT * FROM user_profile WHERE username = ? OR user_email = ?"; 
    PreparedStatement stmt = conn.prepareStatement(sql); 
    stmt.setString(1, username); 
    stmt.setString(2, email); 

    ResultSet res = stmt.executeQuery(); 

    // Utilize a boolean Flag to indicate whether 
    // or not the User is registered. 
    boolean registered = false; 
    while (res.next()) { 
     if(res.getString("username").equalsIgnoreCase(username)) { 
      JOptionPane.showMessageDialog(registerPanel, 
        "The username has already been already registered!"); 
      registered = true; 
      break; // Get out of the loop. No more need for it. 
     } 
     else if(res.getString("user_email").equalsIgnoreCase(email)) { 
      JOptionPane.showMessageDialog(registerPanel, 
        "This email address has already been already registered!"); 
      registered = true; 
      break; // Get out of the loop. No more need for it. 
     } 
    } 

    // Do what needs to be done if User is NOT registered. 
    if (!registered) { 
     ............................... 
     ............................... 
    } 
    res.close(); 
    stmt.close(); 
    conn.close(); //Close the DB connection 
} 
catch (SQLException ex) { 
    ex.printStackTrace(); 
} 

你會發現使用PreparedStatement類。使用此類有許多好處：

1）PreparedStatement允許您編寫動態參數查詢。

2）PreparedStatement比使用Java中的Statement更快。

3）的PreparedStatement防止SQL注入攻擊在Java中

瞭解更多關於Why to use Prepared Statements in Java here。