java.sql.SQLException：对空结果集的非法操作。在验证时 [英] java.sql.SQLException: Illegal operation on empty result set. when authenticating

问题描述

我要做的是：

1. 接受用户名（uname）和密码（passw）作为输入来自用户。

1. Accept username(uname) and password(passw) as an input from the user.

使用 ResultSet ，检索唯一的元组，数据库中的用户名和用户提供的用户名套装。此元组将包含用户名和密码。

Using ResultSet, retrieve the only tuple, to which username in the database and username given by user suits. This tuple will contain username and password.

如果用户提供的密码也适合数据库中的密码，则显示两个creadentials正确的消息否则其中一个是错的。

If the password given by user also suits the password in the database, the display the message that both creadentials are correct else one of them is wrong.

除一例外，一切正常。当用户名本身错误时，mysql根本找不到该属性，并且会给出以下错误： java.sql.SQLException：对空结果集的非法操作。

Everything works fine except in one case. When the username itself is wrong, the mysql will not find the attribute at all and will give this error: java.sql.SQLException: Illegal operation on empty result set.

代码是：

ok.addActionListener(new ActionListener()
    {
        public void actionPerformed(ActionEvent ae)
        {
            String uname=jf1.getText();
            String passw=jf2.getText();
            String n;
            String m;
            try
            {
                Class.forName("com.mysql.jdbc.Driver").newInstance();
                Connection conn = DriverManager.getConnection("jdbc:mysql://localhost/authentication?" + "user=root&password=letmein");
                PreparedStatement stmt=conn.prepareStatement("Select * from admin where id = ?");
                stmt.setString(1,uname);
                ResultSet rs=stmt.executeQuery();
                rs.next();
                n=rs.getString("id");
                m=rs.getString("pass");
                conn.close();
                if(n.equalsIgnoreCase(uname) && m.equalsIgnoreCase(passw))
                {
                    JOptionPane.showMessageDialog(null,"Username and password is correct");
                }
                else
                {
                    JOptionPane.showMessageDialog(null,"Username or password is not correct");
                }

            }
            catch(Exception ex)
            {
                  System.out.println(ex);
            }
        }//end of actionperformed
    });//end of actionlistener

我有什么方法可以一次完成两个操作（在关闭与数据库的连接之前）？如果没有，那么替代方法是什么？

Is there any way I can do both operations at a time (before closing the connection with database)?. If not, what's the alternative method?

推荐答案

你应该使用 rs.next的结果（）：

            if (rs.next()) {
                n=rs.getString("id");
                m=rs.getString("pass");
            }

如果 rs.next（）返回false，这表示查询没有返回任何行。

If rs.next() returns false, this means the query returned no rows.

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