java + app engine + cloudSQL + spring/hibernate

Question

I am using Spring Hibernate with app engine and cloudSQL for my project but i am getting one error frequently. This occurs when application becomes ideal for sometimes.

For every query (fetching or save/update to database), i open session and close session after its use. like this -- My code for database fetching is

try{ 
        Session session = getSessionFactory().openSession();
        if(session != null)
        {

        List<Account> accounts = session.createQuery("from " + this.clazz.getName() + " where subDomainName = '"+subDomain+"'").list();

        session.close();

        if(accounts != null)
        {
            if(accounts.size()>0){
                return accounts.get(0);
            }
            else{
                return null;
            }
        }
        else
        {
            return null;
        }
        }
        else {
            return null;
        }
        }
        catch(Exception e){
            log.info("Error in retriving subdomain details :: in Account Dao");
            return null;

        }

I am using Autowired structuring. but when application becomes ideal for sometime and after some time when i refresh page its display the error as Stream Closed of CloudSQL on app engine, error is shown below...

Error is :

6 Jan, 2014 6:21:04 AM com.google.appengine.repackaged.org.apache.http.impl.client.DefaultRequestDirector handleResponse
WARNING: Authentication error: Unable to respond to any of these challenges: {bearer=WWW-Authenticate: Bearer realm="https://www.google.com/accounts/AuthSubRequest", error=invalid_token}
6 Jan, 2014 6:21:04 AM com.google.appengine.api.rdbms.dev.LocalRdbmsServiceRemoteDriver openConnection
WARNING: openConnection
java.sql.SQLException: Stream closed
    at com.google.cloud.sql.jdbc.internal.googleapi.RpcGoogleApi.newOpenConnectionIOException(RpcGoogleApi.java:187)
    at com.google.cloud.sql.jdbc.internal.googleapi.RpcGoogleApi.openConnection(RpcGoogleApi.java:105)
    at com.google.appengine.api.rdbms.dev.LocalRdbmsServiceRemoteDriver.openConnection(LocalRdbmsServiceRemoteDriver.java:206)
    at com.google.appengine.api.rdbms.dev.LocalRdbmsService.openConnection(LocalRdbmsService.java:119)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.google.appengine.tools.development.ApiProxyLocalImpl$AsyncApiCall.callInternal(ApiProxyLocalImpl.java:498)
    at com.google.appengine.tools.development.ApiProxyLocalImpl$AsyncApiCall.call(ApiProxyLocalImpl.java:452)
    at com.google.appengine.tools.development.ApiProxyLocalImpl$AsyncApiCall.call(ApiProxyLocalImpl.java:430)
    at java.util.concurrent.Executors$PrivilegedCallable$1.run(Executors.java:461)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.util.concurrent.Executors$PrivilegedCallable.call(Executors.java:458)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
    at java.util.concurrent.FutureTask.run(FutureTask.java:138)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
    at java.lang.Thread.run(Thread.java:662)
Caused by: java.io.IOException: Stream closed
    at java.util.zip.GZIPInputStream.ensureOpen(GZIPInputStream.java:42)
    at java.util.zip.GZIPInputStream.read(GZIPInputStream.java:85)

For this to engage app engine and cloudSQL i have wriiten cron job of certains request but this is not feasible solution, i can not gets why cloudSQL closes its stream for app engine.