| 一個(gè)stmt多個(gè)rs進(jìn)行操作引起的ResultSet已經(jīng)關(guān)閉錯誤 |
| 2005-08-09 來(lái)源:CSDN 作者:yizdream |
| 一個(gè)stmt多個(gè)rs進(jìn)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(huì )引起rs已經(jīng)關(guān)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();//由于執行了rst=stmt.executeQuery(sql_a);rs就會(huì )被關(guān)閉掉！所以程序執行到此會(huì )提示ResultSet已經(jīng)關(guān)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(gè)stmt最好對應一個(gè)rs, 如果用一個(gè)時(shí)間內用一個(gè)stmt打開(kāi)兩個(gè)rs同時(shí)操作，會(huì )出現這種情況. 所以解決此類(lèi)問(wèn)題:1.就多創(chuàng )建幾個(gè)stmt,一個(gè)stmt對應一個(gè)rs;2.若用一個(gè)stmt對應多個(gè)rs的話(huà),那只能得到一個(gè)rs后就操作,處理完第一個(gè)rs后再處理其他的,如上"正確代碼". 多個(gè)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(); |
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