在将其标记为重复之前,请注意,我查看了关于在stackoverflow上存在的空指针异常的线程。不幸的是,我还没有设法解决这个问题,如果有人能指引我走向正确的方向,我会感激不尽,因为我现在陷入了一段时间。Java/MySQL准备语句错误
我正在一个错误
显示java.lang.NullPointerException在 sample.LoginWindow.setBtnLogin(LoginWindow.java:39))点在 以下行了PreparedStatement.setString(1,txtUserName.getText ()
我有DBUtilities
类握住我的数据库连接,并关闭一些方法:
public class DBUtilities {
// Getting connection to the database.
public static Connection getConnection() throws SQLException {
String url = "jdbc:mysql://localhost:3306/studentmanagementdb";
String user = "admin";
String pass = "administrator";
Connection connection = DriverManager.getConnection(url, user, pass);
return connection;
}
// Close prepared statement.
public static void closePreparedStatement(PreparedStatement pStmt) {
try {
if(pStmt != null) {
pStmt.close();
}
}catch(SQLException sExepction) {
showErrorMsg("SQL Database Error:", "Prepared Statement could not be closed.");
}
}
// Close result set.
public static void closeResultSet(ResultSet resSet) {
try {
if (resSet != null){
resSet.close();
}
}catch (SQLException sException) {
showErrorMsg("SQL Database Error:", "Result Set could not be closed.");
}
}
public static void closeConnection(Connection connect) {
try {
if(connect != null) {
connect.close();
}
}catch (SQLException sException) {
showErrorMsg("SQL Database Error:", "Database Connection could not be close.");
}
}
// Shows error message.
public static void showErrorMsg(String title, String msg) {
Platform.runLater(() -> {
Alert alert = new Alert(Alert.AlertType.ERROR);
alert.setTitle(title);
alert.setHeaderText(msg);
alert.setWidth(200);
alert.setHeight(200);
alert.showAndWait();
});
}
}
类,它使用的连接:
public class LoginWindow implements Initializable{
@FXML
private TextField txtUserName;
@FXML
private PasswordField txtPassword;
@FXML
private Button btnLogin;
Connection connection = null;
PreparedStatement preparedStatement = null;
ResultSet resultSet = null;
DBUtilities dbUtil = new DBUtilities();
// Setting the login button.
@FXML
private void setBtnLogin(ActionEvent event) {
try {
connection = dbUtil.getConnection();
String sqlQuery = "SELECT * FROM 'User_Login_Details' WHERE 'User_Name' = ? AND 'User_Password' = ?";
connection.prepareStatement(sqlQuery);
preparedStatement.setString(1, txtUserName.getText());
preparedStatement.setString(2, txtPassword.getText());
resultSet = preparedStatement.executeQuery();
}catch (Exception exception) {
//dbUtilities.showErrorMsg("Database Connection Error:", "Could not connect to the database.");
exception.printStackTrace();
}finally {
dbUtil.closePreparedStatement(preparedStatement);
dbUtil.closeResultSet(resultSet);
dbUtil.closeConnection(connection);
}
}
@Override
public void initialize(URL location, ResourceBundle resources) {
btnLogin.setOnAction(this::setBtnLogin);
}
}
'preparedStatement' not initialised – Satya
PreparedStatement preparedStatement = null;然后connection.prepareStatement(sqlQuery);.这是不够的?对不起,我是mySQL的新手。 – helloumarian
它返回一个PreparedStatement。你需要捕捉它。 https://docs.oracle.com/javase/7/docs/api/java/sql/Connection.html#prepareStatement(java.lang.String) –