java - ResultSet 关闭后不允许操作？

Question

据我了解，当 ResultSet 一次只能打开一次时，就会出现此问题。所以我添加了更新

try
{          
  String sql = "SELECT * FROM test;
  ResultSet rs = stmt.executeQuery(sql);

  if(rs.next()){
    do {
        if(rs.getString("sent").equals("0")) {
            try {

                //update

                try {
                    String psSQL = "UPDATE sent SET ..........";
                    updateStatement = conn.prepareStatement(psSQL);
                    updateStatement.setString(1, ....);
                    updateStatement.setString(2, ....);
                    updateStatement.setString(3, ...);

                    updateStatement.executeUpdate();
                    System.out.println("Record updated");
                } catch (SQLException e) {
                    System.out.println(e.getMessage());
                } finally {
                    if(updateStatement != null) {
                        updateStatement.close();
                    }
                    if (conn != null) {
                        conn.close();
                    }
                }

            } catch (MessagingException mex) {
             mex.printStackTrace();
            }
        }
    } while(rs.next()); **<---- Still same Error here**
  } else if (rs.getRow() == 0) {
    if (!mailSender.equals(".....")) {
        try{
                //insert

             try {
                    String psSQL2 = "INSERT INTO sent"
                            + "(......) VALUES"
                            + "(?,?,?)";
                    insertStatement = conn.prepareStatement(psSQL2);
                    insertStatement.setString(1, ...);
                    insertStatement.setString(2, ....);
                    insertStatement.setString(3, ....);

                    insertStatement.executeUpdate();
                    System.out.println("Insert done!");
             } catch (SQLException e) {
                System.out.println(e.getMessage());
             } finally {
                if(insertStatement != null) {
                    insertStatement.close();
                }
                if (conn != null) {
                    conn.close();
                }
             }                 
          }catch (MessagingException mex) {
             mex.printStackTrace();
          }
    } else {
        return null;
    }
  }
}
catch (SQLException se)
{
  se.printStackTrace();
}
catch (Exception e)
{
  e.printStackTrace();
}
finally
{
  try
  {
    if (stmt != null) {
      stmt.close();
    }
  }
  catch (SQLException se2) {}
  try
  {
    if (conn != null) {
      conn.close();
    }
  }
  catch (SQLException se)
  {
    se.printStackTrace();
  }
}

所以.. while(rs.next()) 运行时出现错误。我在 rs.next() while 循环之前和之后放入了一个 system.out.println，并在该 while 循环之后放入了第 n 个母 pig 。

我尝试使用另一个结果集 rs2，但它也不起作用，所以我不知道这个问题是从哪里来的..

Answer 1

完成您想要的操作的更好方法是使用单个 ResultSet

  String sql = "SELECT * FROM test";
  ResultSet rs = stmt.executeQuery(sql);

  if(rs.next()){
      do {

        if (rs.getString("sent").equals("0")) {

          try{
             //if there is a row and it is equals to 0.. so update it to 1.. 

             String sql2 = "UPDATE test SET test='1' WHERE test=....";
             Statement updateStatement = <create statement here>;

             int rs3 = updateStatement.executeUpdate();
             updateStatement.close();
          }catch (SQLException sqlex) { 
             sqlex.printStackTrace();
          }
        }
     }while(rs.next());
   }else {
      try{
             //insert if i couldn't get any rows in the table
             String sql2 = "INSERT INTO test......";
             Statement insertStatement = <create statement here>;
             int rs3 = insertStatement.executeUpdate();
             insertStatement.close();
          }catch (SQLException sqlex) {
             sqlex.printStackTrace();
          }
    }

    rs.close();
    stmt.close();
    conn.close(); 

希望这有帮助。