java.sql.SQLException: 结果集开始前已经有rs.next

Question

所以我正在连接到数据库，我想从 table 投票中获取奶牛编号以在条形图上显示它，但我收到错误 "java.sql.SQLException: Before start of result set" 但我有 rs.next 有人可以帮我吗

conn = DbCon.ConnectDb();
String sql = "SELECT * FROM votes";
try
{
      pst = conn.prepareStatement(sql);
      rs = pst.executeQuery();
      String cows = rs.getString("cows");
      if (rs.next())
      {
          int cowss = Integer.parseInt(cows);
          DefaultCategoryDataset dataset=new DefaultCategoryDataset();
          dataset.setValue(cowss ,"Votes", "Cows");
          dataset.setValue(20 ,"Votes", "Pigs");
          dataset.setValue(20 ,"Votes", "Dogs");
          dataset.setValue(50 ,"Votes", "Donkeys");
          JFreeChart chart = ChartFactory.createBarChart("Results", "", "Votes", dataset, PlotOrientation.VERTICAL , false, true, true);
          ChartFrame frame = new ChartFrame("Results", chart);
          frame.setVisible(true);
          frame.setSize(450,350);
          frame.setLocationRelativeTo(null);
          frame.setResizable(false);
     }
 }
 catch(Exception e)
 {
     JOptionPane.showMessageDialog(null, e);
 }

Answer 1

您需要在读取列值之前调用ResultSet.next()，以便光标指向结果中的第一行：

if (rs.next()) { String cows = rs.getString("cows"); int cowss = Integer.parseInt(cows); ...

您在这里也真的不需要 PreparedStatement -- 没有参数化查询。您可以简单地使用正常的 Statement.

java.sql.SQLException: 结果集开始前已经有rs.next

java.sql.SQLException: Before start of result set already have rs.next

java

sql

jdbc