PSQLException：ResultSet放置不正确，也许您需要调用下一个 [英] PSQLException: ResultSet not positioned properly, perhaps you need to call next

问题描述

public UserBean authenticate(String username,String password){
    PostGresDAO pg=new PostGresDAO();   //creates new connection
    Connection conn=pg.getConnecion();  //return connection object
    PreparedStatement ps;
    ResultSet rs;
    String query="select password,name from scg_users where username=?";
    UserBean ub=null;
    boolean authenticated=false;
    try{
        ps=conn.prepareStatement(query);
        ps.setString(1, username);
        rs=ps.executeQuery();

        if(rs!=null){

            authenticated=password.equals(rs.getString(1));  //exception raised here
            if(authenticated){
                ub=new UserBean();
                ub.setUser(rs.getString(2));
                ub.setUsername(username);
            }
        }
    }
    catch(SQLException e){
        e.printStackTrace();
    }
    return ub;
}

我正在使用此代码对用户进行身份验证。用户名和密码是从request参数中提取的，并传递到此方法进行身份验证。但是它抛出：

I am using this code for authenticating a user. The username and password are extracted from the request parameter and passed onto this method for authentication. But it throws a:

org.postgresql.util.PSQLException: ResultSet not positioned properly, perhaps you need to call next.

请咨询。

推荐答案

错误告诉您恰好出了什么问题-您没有在ResultSet上调用 next（）来获取结果的第一行。

The error is telling you exactly what's wrong - you're not calling next() on your ResultSet to get to the first row of the results.

此行：

if(rs!=null)

是毫无意义的；我认为 executeQuery 不会返回null。如果您的查询有问题，将引发异常。如果没有结果，它将返回一个空结果集。要查看是否有一行，应调用 next（）并检查返回值：

is pointless as far as I know; I don't believe executeQuery will ever return null. If there's a problem in your query, an exception will be thrown. If there are no results, it will return an empty result set. To see if there's a row, you should call next() and check the return value:

if (rs.next())

另外：

• 捕获异常并仅打印堆栈跟踪而不进行重新抛出几乎总是错误的方法


• 您的代码建议您以纯文本格式存储密码。请不要真的，真的不是。

• Catching an exception and just printing the stack trace without rethrowing is almost always the wrong approach
• Your code suggests that you're storing passwords in plain text. Please don't. Really, really don't.

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