ImplementingHibernateLongSessions

Implementing the Hibernate long-session-pattern

Being asked about how to use long hibernate sessions with Hivemind a couple of times on the Tapestry-Users-List - Here is what I did:

Overview

Basically all one needs to accomplish this is

• a persistence service which I called ClientStateStorage. It can be provided with an http session as the underlying storage mechanism for production (via a servlet filter). Otherwise it uses a simple Map for testing.

• a service-model extending AbstractServiceModelImpl which works much like the PooledServiceModel, the differences being firstly, that it comes with a different lifecycle and, secondly that it doesn't store service-implementations in a pool common to all clients but in the aforementioned ClientStateStorage.

Implementation

Here is the hivemodule.xml making the new service-model available to other modules. As well, it provides a very simple schema to configure the Hibernate Session Factory.

<?xml version="1.0"?>
<module id="scm.hivemind" version="1.0.0" 
                package="scm.hivemind.statefulservice">
   
  <contribution configuration-id="hivemind.ServiceModels">
    <service-model class="StatefulServiceModelFactory" 
                           name="stateful"/>
  </contribution>
  
  <service-point id="ClientStateStorage">
    <invoke-factory model="pooled"> 
                <construct class="ClientStateStorageImpl" />
    </invoke-factory>
  </service-point>
         
   <schema id="HibernateSessionFactory">
      <element name="property">
        a hibernate property       
        <attribute name="name" required="true">
          the property name
        </attribute>  
        <attribute name="value">
          the value ( as in config.hbm.xml without the leading "hibernate.")
        </attribute> 
        <conversion class="scm.hivemind.hibernate.HibernateProperty"/>
      </element>
      <element name="config-xml">
        the hibernate config.xml File       
        <attribute name="name" required="true">
           the name of the config.xml file
        </attribute>  
        <conversion class="scm.hivemind.hibernate.HibernateConfigFile"/>
      </element>
    </schema>
 
</module>

Java-Code

Here's the Java Code:

Client-State-Store

• ClientStateStorage

• ClientStateStorageImpl

• StateStorageClearanceListener

• StatefulHivemindFilter

service-model stuff

• StatefulServiceModel

• StatefulServiceModelFactory

• StatefulServiceLifecycleListener

the hibernate session-factory

• HibernateSessionFactory

• HibernateProperty

• HibernateConfigFile

Usage

The following snippet from an applications hivemodule.xml shows how to configure long hibernate Session which then can be injected into the app-specific services.

<service-point id="DWKHibernateSession" interface="net.sf.hibernate.Session">
     The hibernate-session itself. 
     <invoke-factory service-id="webkit.awk.DWKSessionFactory" 
                                 model="stateful"/>
  </service-point>
  
  <configuration-point id="DWKSessionFactory" 
                        schema-id="scm.hivemind.HibernateSessionFactory"/>
                        
  <contribution configuration-id="DWKSessionFactory" >
          <config-xml name="/scm/extranet/domain/hibernate.cfg.xml"/> 
          <property name="dialect" value="net.sf.hibernate.dialect.OracleDialect"/>
          <property name="cache.provider_class" value="net.sf.ehcache.hibernate.Provider"/>
          <property name="cache.use_query_cache" value="true"/>
  </contribution>
  
  <service-point id="DWKSessionFactory"  
                 interface="org.apache.hivemind.ServiceImplementationFactory">
        <invoke-factory model="singleton">
                <construct
                class="scm.hivemind.hibernate.HibernateSessionFactory"
            initialize-method="init">
                        <configuration>DWKSessionFactory</configuration>
        </construct>                            
        </invoke-factory>       
        <interceptor service-id="hivemind.LoggingInterceptor"/>
  </service-point>
  

In a real web-application you would have to configure the StatefulHivemindFilter for your controller Servlet.

Precautions

• Take care to avoid concurrent requests to your controller servlet (sync on the session or something)

• While the stuff will work on a cluster, it won't support transparent failover of sessions, because the Hivemind-Proxies don't serialize instance state.