mysql - JBDC和MYSQL空值插入表

Question

下面是简单的登录系统。目前，它允许我在表中输入空白的用户名和密码，即使每个索引都指定为 NOT NULL？它不允许我输入重复项，这正是我想要的，但是如何捕获输入的空白​​参数？我错过了什么？

注册Servlet

....
LoginService loginService = new LoginService();
            connection = loginService.getConnection(connection);
            loginService.addNewUser(preparedStatement, connection, newUserId, newUserPassword, newUserFirstName, newUserLastName);
...

LoginService方法addNewUser

public void addNewUser(PreparedStatement ps, Connection connection, String newUserId, String newUserPassword,String newUserFirstName,String newUserLastname) throws SQLException
    {
        ps = connection.prepareStatement("INSERT INTO users (userId ,password , userFirstName, userLastName)VALUES(?,?,?,?)");
        ps.setString(1, newUserId);
        ps.setString(2, newUserPassword);
        ps.setString(3, newUserFirstName);
        ps.setString(4, newUserLastname);

        ps.executeUpdate();

    }

Answer 1

要解决当前问题，您可以将其添加到 addNewUser 方法的开头(行之前: ps = connection.prepareStatement("...");)

if (newUserId != null && "".equals(newUserId.trim()))
    newUserId = null;
if (newUserPassword != null && "".equals(newUserPassword.trim()))
    newUserPassword = null;

您应该在 JDBC 参数中传递真正的 NULL 值(空字符串不够好)