| 一個stmt多個rs進行操作引起的ResultSet已經關閉錯誤 |
| 2005-08-09 來源:CSDN 作者:yizdream |
| 一個stmt多個rs進行操作. 那么從stmt得到的rs1,必須馬上操作此rs1后,才能去得到另外的rs2,再對rs2操作. 不能互相交替使用,會引起rs已經關閉錯誤. 錯誤的代碼如下: stmt=conn.createStatement(); rs=stmt.executeQuery("select * from t1"); rst=stmt.executeQuery("select * from t2"); rs.last();//由于執(zhí)行了rst=stmt.executeQuery(sql_a);rs就會被關閉掉！所以程序執(zhí)行到此會提示ResultSet已經關閉.錯誤信息為:java.sql.SQLException: Operation not allowed after ResultSet closed rst.last(); 正確的代碼: stmt=conn.createStatement(); rs=stmt.executeQuery("select * from t1"); rs.last();//對rs的操作應馬上操作,操作完后再從數據庫得到rst,再對rst操作 rst=stmt.executeQuery("select * from t2"); rst.last(); 原因是: The object used for executing a static SQL statement and returning the results it produces. By default, only one ResultSet object per Statement object can be open at the same time. Therefore, if the reading of one ResultSet object is interleaved with the reading of another, each must have been generated by different Statement objects. All execution methods in the Statement interface implicitly close a statment‘s current ResultSet object if an open one exists. 一個stmt最好對應一個rs, 如果用一個時間內用一個stmt打開兩個rs同時操作，會出現這種情況. 所以解決此類問題:1.就多創(chuàng)建幾個stmt,一個stmt對應一個rs;2.若用一個stmt對應多個rs的話,那只能得到一個rs后就操作,處理完第一個rs后再處理其他的,如上"正確代碼". 多個stmt對應各自的rs. stmt=conn.createStatement(); stmt2=conn.createStatement(); rs=stmt.executeQuery("select * from t1"); rst=stmt2.executeQuery("select * from t2"); rs.last(); rst.last(); |
