一个stmt多个rs进行操作引起的ResultSet已经关闭错误
类别: JAVA教程 
一个stmt多个rs进行操作.那么从stmt得到的rs1,必须马上操作此rs1后,才能去得到另外的rs2,再对rs2操作.不能互相交替使用,会引起rs已经关闭错误.错误的代码如下: stmt=conn.createStatement(); rs=stmt.executeQuery("select * from t1"); rst=stmt.executeQuery("select * from t2"); rs.last();//由于执行了rst=stmt.executeQuery(sql_a);rs就会被关闭掉！所以程序执行到此会提示ResultSet已经关闭.错误信息为:java.sql.SQLException: Operation not allowed after ResultSet closed rst.last();正确的代码: stmt=conn.createStatement(); rs=stmt.executeQuery("select * from t1"); rs.last();//对rs的操作应马上操作,操作完后再从数据库得到rst,再对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. 一个stmt最好对应一个rs, 如果用一个时间内用一个stmt打开两个rs同时操作，会出现这种情况.所以解决此类问题:1.就多创建几个stmt,一个stmt对应一个rs;2.若用一个stmt对应多个rs的话,那只能得到一个rs后就操作,处理完第一个rs后再处理其他的,如上"正确代码".多个stmt对应各自的rs.stmt=conn.createStatement();stmt2=conn.createStatement();rs=stmt.executeQuery("select * from t1");rst=stmt2.executeQuery("select * from t2");rs.last();rst.last();
