初次使用无状态sessionbean的问题

huim

无状态sessionbean的方法test()中,两次从Datasource取连接,
     如果前一连接在取得之后,什么也不做便关闭,则后一连接的AutoCommit()值为true;
     如果前一连接有做查询的话,为什么后一连接的AutoCommit值会为false??
     (注:此sessionbean的事务设置为容器管理)

     如果将此方法放到普通的javabean里来实现,则方法中取得的两次连接的AutoCommit()值均为true,

     请问这是为什么??

     测试代码如下:

测试一:
public void test() throws SQLException, Exception {
System.out.println("test1");
Context ictx1 = new InitialContext();
DataSource ds1 = (DataSource) ictx1.lookup("JNDI/SIDB");
Connection conn1=ds1.getConnection();
System.out.println("conn1.getAutoCommit()="+conn1.getAutoCommit());
conn1.close();

Context ictx2 = new InitialContext();
DataSource ds2 = (DataSource) ictx2.lookup("JNDI/SIDB");
Connection conn2=ds2.getConnection();
System.out.println("conn2.getAutoCommit()="+conn2.getAutoCommit());
conn2.close();
}

运行结果:
[07-2-1 11:00:48:969 CST] 462c89fd SystemOut     O test1
[07-2-1 10:58:53:203 CST]  896c9e5 SystemOut     O conn1.getAutoCommit()=true
[07-2-1 10:58:53:219 CST]  896c9e5 SystemOut     O conn2.getAutoCommit()=true

测试二:
public void test() throws SQLException, Exception {
System.out.println("test2");
Context ictx1 = new InitialContext();
DataSource ds1 = (DataSource) ictx1.lookup("JNDI/SIDB");
Connection conn1=ds1.getConnection();
System.out.println("conn1.getAutoCommit()="+conn1.getAutoCommit());

PreparedStatement pstmt=conn1.prepareStatement("select * from sysuser");
ResultSet rs=pstmt.executeQuery();

rs.close();
pstmt.close();
conn1.close();

Context ictx2 = new InitialContext();
DataSource ds2 = (DataSource) ictx2.lookup("JNDI/SIDB");
Connection conn2=ds2.getConnection();
System.out.println("conn2.getAutoCommit()="+conn2.getAutoCommit());
conn2.close();
}
运行结果:

[07-2-1 11:00:48:969 CST] 462c89fd SystemOut     O test2
[07-2-1 11:00:48:969 CST] 462c89fd SystemOut     O conn1.getAutoCommit()=true
[07-2-1 11:00:48:984 CST] 462c89fd SystemOut     O conn2.getAutoCommit()=false(****区别之处****)