sae mysql hibernate 30秒断开连接的问题

问题是这样的，我的微信公众号后台放在sae上，使用的是proxool连接池，刚部署时，可以正常读取数据库，每当过几分钟后数据库连接就异常了。ps：本地测试正常
101.226.62.81 [29/May/2015:20:47:23 +0800] JAVA_Error: Couldn't perform the operation prepareStatement: You can't perform any operations on this connection. It has been automatically closed by Proxool for some reason (see logs). yq34.javaruntime

sae提示我说是使用了关闭的连接，我在hibernate中每次操作后都session关闭了。
proxool配置如下
28000
10

0
20
0

true
true
select id from test

因为sae中mysql在没有连接后的30秒自动断开数据库连接，所以我把检查时间设置为了28秒，但是还是出现了空连接，请教大神帮忙解决。

 <house-keeping-sleep-time>28000</house-keeping-sleep-time>
<maximum-new-connections>10</maximum-new-connections>  
<prototype-count>0</prototype-count>
<maximum-connection-count>20</maximum-connection-count>
<minimum-connection-count>0</minimum-connection-count>

 <test-before-use>true</test-before-use>
 <test-after-use>true</test-after-use>
  <house-keeping-test-sql>select id from test</house-keeping-test-sql>