Java - preparedstatement

Question

ResultSet rs;

PreparedStatement st = MyConnection.prepareStatement("Select * from logindetails where Username = ? and Password = ?");

st.setString(1, username);
st.setString(2, password);

while (rs.next() )
{
    //login correct = true, redirect
}

rs.close();
MyConnection.close();

这个问题是我不能使用PreparedStatement在while循环中使用next（），因为我想用用户输入的参数搜索数据库。

我该如何解决这个问题？

Answer 1

您不需要while (rs.next())，因为您的PreparedStatement已使用您设置的用户名和密码查询了结果集。而是使用if语句来测试结果集： -

// returns AuthenticatedUser object if authentication is successful, otherwise null
public AuthenticatedUser authenticate(String username, String password) {   
    PreparedStatement st = ...;
    st.setString(1, username);
    st.setString(2, password);

    ResultSet rs = st.executeQuery();

    AuthenticatedUser user = null;

    //login valid because there is something from the result set, then create user object
    if (rs.next() ) {
        // set all the useful user information in this POJO
        user = new AuthenticatedUser(username, rs.getString("name"), rs.getString("whatever_important_info"));
    }

    ... // close resultset, preparedStatement, connection, clean up, etc.

    return user;  
}

从你的服务器/控制器，你可以做这样的事情来处理页面重定向： -

// call the method above to get the user object based on the provided username and password
AuthenticatedUser user = dao.authenticate(username, password);

// successful authentication
if (user != null) {
   // set user object in session so that you don't need to query the database for user info again and again
   session.setAttribute("user", user); 

   // redirect to welcome page
   request.getRequestDispatcher("/your-welcome-page").forward(request, response);
}
else {
   // redirect to login page if authentication fails
   request.getRequestDispatcher("/login-page").forward(request, response);
}

Answer 2

不确定我是否正确理解了您的问题，但我猜您想要遍历结果集并访问列数据......

rs = st.executeQuery();

while (rs.next() ) {
       rs.getString("columnname");
}

Answer 3

如果这是用于生产应用程序（而不是学习或家庭作业），为什么不使用像iBatis这样的抽象层来隔离这个生物传感器呢？