java - JDBC 从其中 x=(?) 选择 *

Question

我正在尝试创建一种从数据库中检索客户并将其存储在对象中的方法。但由于某种原因我的sql语句不起作用。

这是我的方法。

    public class CustomerDAO {

private String url = "jdbc:h2:tcp://localhost/project;IFEXISTS=TRUE";

Set<Customer> customerCollection = new TreeSet<>();


public Customer loginCustomer(String user,String pass) throws SQLException{

    String sql = "SELECT * FROM Customers WHERE USERNAME=(?) AND PASSWORD=(?) ;";

    try(
        //get connection form database
        Connection dbCon = JdbcConnection.getConnection(url);
        //create a statement
        PreparedStatement stmt = dbCon.prepareStatement(sql);                   
        ){

        stmt.setString(1, user);
        stmt.setString(2, pass);

        ResultSet rs = stmt.executeQuery();

        Customer c = new Customer(rs.getString("username"), rs.getString("name"), rs.getString("email"),
                                    rs.getString("address"), rs.getString("creditCardDetails"), rs.getString("password"));


        if(c.getUsername().contains(user))
            return c;
        else
            return null;


}catch (SQLException ex){
        throw new RuntimeException(ex);
    }

}

我用这个测试了

        public static void main(String[] args) throws SQLException {

    CustomerDAO dao = new CustomerDAO();

    Customer c = dao.loginCustomer("jesus", "1234");

    System.out.println(c.getName());
    System.out.println(c.getPassword());
    System.out.println(c.getAddress());



}

}

但我收到这些错误。

        Exception in thread "main" java.lang.RuntimeException: org.h2.jdbc.JdbcSQLException: No data is available [2000-187]
    at DAO.CustomerDAO.loginCustomer(CustomerDAO.java:54)
    at web.NewMain.main(NewMain.java:25)
Caused by: org.h2.jdbc.JdbcSQLException: No data is available [2000-187]
    at org.h2.message.DbException.getJdbcSQLException(DbException.java:345)
    at org.h2.message.DbException.get(DbException.java:179)
    at org.h2.message.DbException.get(DbException.java:155)
    at org.h2.message.DbException.get(DbException.java:144)
    at org.h2.jdbc.JdbcResultSet.checkOnValidRow(JdbcResultSet.java:3186)
    at org.h2.jdbc.JdbcResultSet.get(JdbcResultSet.java:3192)
    at org.h2.jdbc.JdbcResultSet.get(JdbcResultSet.java:3209)
    at org.h2.jdbc.JdbcResultSet.getString(JdbcResultSet.java:302)
    at DAO.CustomerDAO.loginCustomer(CustomerDAO.java:43)
    ... 1 more
Java Result: 1

直接从数据库控制台运行该语句效果很好。例如

SELECT * FROM Customers WHERE USERNAME='jesus' AND PASSWORD='1234' ;

Answer 1

您必须将光标移动到下一行:添加

rs.next();

之后:

 ResultSet rs = stmt.executeQuery();