The connection does not exist + as400 + hibernate

Hello,
We are faced with the following problem: our db (db2 as400) is restarted on a weekly basis and every Monday morning a user trying to connect to our Hibernate tomcat application gets the exception below and we have to restart tomcat. How can we configure tomcat or hibernate so that this no longer happens?
Any clue welcome,
Julien.

java.sql.SQLException: The connection does not exist.
com.ibm.as400.access.JDError.throwSQLException(JDError.java:389)
com.ibm.as400.access.AS400JDBCConnection.checkOpen(AS400JDBCConnection.java:400)
com.ibm.as400.access.AS400JDBCConnection.getAutoCommit(AS400JDBCConnection.java:808)
org.hibernate.connection.DriverManagerConnectionProvider.getConnection(DriverManagerConnectionProvider.java:104)
org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:423)
org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:144)
org.hibernate.jdbc.AbstractBatcher.prepareQueryStatement(AbstractBatcher.java:139)
org.hibernate.loader.Loader.prepareQueryStatement(Loader.java:1547)
org.hibernate.loader.Loader.doQuery(Loader.java:673)
org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:236)
org.hibernate.loader.Loader.doList(Loader.java:2220)
org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2104)
org.hibernate.loader.Loader.list(Loader.java:2099)
org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:378)
org.hibernate.hql.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:338)
org.hibernate.engine.query.HQLQueryPlan.performList(HQLQueryPlan.java:172)
org.hibernate.impl.SessionImpl.list(SessionImpl.java:1121)
org.hibernate.impl.QueryImpl.list(QueryImpl.java:79)
org.hibernate.ejb.QueryImpl.getResultList(QueryImpl.java:66)
com.newedge.cdr.util.PopulateUtil.retrieveCodaClients(PopulateUtil.java:53)
com.newedge.cdr.revaluation.RevaluationResultsManagedBean.<init>(RevaluationResultsManagedBean.java:28)
sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
java.lang.reflect.Constructor.newInstance(Constructor.java:494)
java.lang.Class.newInstance0(Class.java:350)
java.lang.Class.newInstance(Class.java:303)
com.sun.faces.mgbean.BeanBuilder.newBeanInstance(BeanBuilder.java:188)
com.sun.faces.mgbean.BeanBuilder.build(BeanBuilder.java:105)
com.sun.faces.mgbean.BeanManager.createAndPush(BeanManager.java:368)
com.sun.faces.mgbean.BeanManager.create(BeanManager.java:222)
com.sun.faces.el.ManagedBeanELResolver.getValue(ManagedBeanELResolver.java:88)
javax.el.CompositeELResolver.getValue(CompositeELResolver.java:53)
com.sun.faces.el.FacesCompositeELResolver.getValue(FacesCompositeELResolver.java:72)
org.apache.el.parser.AstIdentifier.getValue(AstIdentifier.java:61)
org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:186)
com.sun.faces.mgbean.BeanBuilder$Expression.evaluate(BeanBuilder.java:551)
com.sun.faces.mgbean.ManagedBeanBuilder$BakedBeanProperty.set(ManagedBeanBuilder.java:606)
com.sun.faces.mgbean.ManagedBeanBuilder.buildBean(ManagedBeanBuilder.java:133)
com.sun.faces.mgbean.BeanBuilder.build(BeanBuilder.java:107)
com.sun.faces.mgbean.BeanManager.createAndPush(BeanManager.java:368)
com.sun.faces.mgbean.BeanManager.create(BeanManager.java:230)
com.sun.faces.el.ManagedBeanELResolver.getValue(ManagedBeanELResolver.java:88)
javax.el.CompositeELResolver.getValue(CompositeELResolver.java:53)
com.sun.faces.el.FacesCompositeELResolver.getValue(FacesCompositeELResolver.java:72)
org.apache.el.parser.AstIdentifier.getValue(AstIdentifier.java:61)
org.apache.el.parser.AstValue.getValue(AstValue.java:103)
org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:186)
org.apache.jasper.el.JspValueExpression.getValue(JspValueExpression.java:101)
javax.faces.component.UIOutput.getValue(UIOutput.java:184)
com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer.getValue(HtmlBasicInputRenderer.java:201)
com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.getCurrentValue(HtmlBasicRenderer.java:284)
com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeEnd(HtmlBasicRenderer.java:154)
javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:856)
org.ajax4jsf.renderkit.RendererBase.renderChild(RendererBase.java:286)
org.ajax4jsf.renderkit.RendererBase.renderChildren(RendererBase.java:262)
org.ajax4jsf.renderkit.html.AjaxOutputPanelRenderer.encodeChildren(AjaxOutputPanelRenderer.java:79)
javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:832)
org.ajax4jsf.renderkit.RendererBase.renderChild(RendererBase.java:282)
org.ajax4jsf.renderkit.RendererBase.renderChildren(RendererBase.java:262)
org.ajax4jsf.renderkit.html.AjaxOutputPanelRenderer.encodeChildren(AjaxOutputPanelRenderer.java:79)
javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:832)
javax.faces.component.UIComponent.encodeAll(UIComponent.java:936)
javax.faces.component.UIComponent.encodeAll(UIComponent.java:942)
com.sun.faces.application.ViewHandlerImpl.doRenderView(ViewHandlerImpl.java:271)
com.sun.faces.application.ViewHandlerImpl.renderView(ViewHandlerImpl.java:202)
org.ajax4jsf.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:108)
org.ajax4jsf.application.AjaxViewHandler.renderView(AjaxViewHandler.java:189)
com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:109)
com.sun.faces.lifecycle.Phase.doPhase(Phase.java:100)
com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:139)
javax.faces.webapp.FacesServlet.service(FacesServlet.java:266)
org.ajax4jsf.webapp.BaseXMLFilter.doXmlFilter(BaseXMLFilter.java:147)
org.ajax4jsf.webapp.BaseFilter.handleRequest(BaseFilter.java:256)
org.ajax4jsf.webapp.BaseFilter.processUploadsAndHandleRequest(BaseFilter.java:362)
org.ajax4jsf.webapp.BaseFilter.doFilter(BaseFilter.java:488)

You might want a cron script that restarts Tomcat for you right after the db comes back online.

Mark