java - jsp在表单上控制服务器端

Question

我想将发送的数据与数据库中的所有数据进行比较。该 coce 仅将日期插入与最后一行进行比较。如何与数据库中的所有行进行比较？...................................................... ................................................

String sData= request.getParameter("idatadata");
        String sAzienda= request.getParameter("idazienda");
        String sCommessa= request.getParameter("idcommessa");



        String date = "";
        String company = "";
        String order = "";




        Connect con = new Connect();

        try {

            Connection connection = con.createConnection();

            Statement statement = connection.createStatement();
            String sql ="SELECT * FROM table";

            ResultSet resultSet = statement.executeQuery(sql);

            while(resultSet.next()) {
            date = resultSet.getString("iddata");
            company = resultSet.getString("idazienda");
            order = resultSet.getString("idcommessa");

            }

            if((sData.equals(date) && sAzienda.equals(company)) && sCommessa.equals(order)) {
            out.print("already sent");
            con.closeConnection(connection);

            } 

            else {

            DbConnect.insertInDb(connection, sData, sOre, sMinuti, sAzienda, sCommessa, sRifInterno);
            dbc.closeConnection(connection);

            response.getWriter().append("ok! ");

            }
        } catch (Exception e) {

            e.printStackTrace();
        }

    }

Answer 1

您只检查最后一行的原因是，每次检索一行时，您的 while 循环都会覆盖您的局部变量:

while(resultSet.next()) {
    // these lines overwrite the local vars for each row
    date = resultSet.getString("iddata");
    company = resultSet.getString("idazienda");
    order = resultSet.getString("idcommessa");
}

但是在进入数据库的下一行之前，您实际上并没有检查循环内的本地变量。您应该将检查添加到循环中:

while(resultSet.next()) {
    date = resultSet.getString("iddata");
    company = resultSet.getString("idazienda");
    order = resultSet.getString("idcommessa");

    // add your check here
    if((sData.equals(date) && sAzienda.equals(company)) && sCommessa.equals(order)) {
        out.print("already sent");
        break;
    } 
}

最好只根据您要查找的数据执行选择。如果没有得到结果，则数据不在数据库中。这种方法效率更高。如果您确实决定走这条路(这是一个好主意)，请使用准备好的语句，这样您就不会在代码中引入 SQL 注入(inject)漏洞。