hi:

in my webapp, I use JPA to store the runtime state,i use this code in VdcService.java which is a sample  java class:

EntityManagerFactory emf =Persistence.createEntityManagerFactory( "org.drools.persistence.jpa" );
Environment env = KnowledgeBaseFactory.newEnvironment();
env.set( EnvironmentName.ENTITY_MANAGER_FACTORY, emf );

 // create a new knowledge session that uses JPA to store the runtime state
StatefulKnowledgeSession ksession = JPAKnowledgeService.newStatefulKnowledgeSession( kbase, null, env );

I put persistence.xml to webRoot/META-INF/  , persistence.xml:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<persistence
    version="1.0"
    xsi:schemaLocation=
        "http://java.sun.com/xml/ns/persistence
         http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd
         http://java.sun.com/xml/ns/persistence/orm
         http://java.sun.com/xml/ns/persistence/orm_1_0.xsd"
    xmlns:orm="http://java.sun.com/xml/ns/persistence/orm"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/persistence">

    <persistence-unit name="org.drools.persistence.jpa" transaction-type="JTA">
        <provider>org.hibernate.ejb.HibernatePersistence</provider>
        <jta-data-source>java:comp/env/jdbc/mysql</jta-data-source>       
    <class>org.drools.persistence.session.SessionInfo</class>
 <class>org.drools.persistence.processinstance.ProcessInstanceInfo</class>
    <class>org.drools.persistence.processinstance.ProcessInstanceEventInfo</class>
    <class>org.drools.persistence.processinstance.WorkItemInfo</class>
   

        <properties>
            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect"/>           
            <property name="hibernate.max_fetch_depth" value="3"/>
            <property name="hibernate.hbm2ddl.auto" value="create" />
            <property name="hibernate.show_sql" value="true" />   
            <property name="hibernate.transaction.manager_lookup_class" value="org.hibernate.transaction.BTMTransactionManagerLookup" />
        </properties>       
    </persistence-unit>
   
</persistence>

I use resin 3.1.10,  $resin-home/conf/resin.conf:

           <database>
           <jndi-name>jdbc/mysql</jndi-name>
           <driver type="org.gjt.mm.mysql.Driver">
             <url>jdbc:mysql://127.0.0.1:3306/test</url>
             <user>root</user>
             <password></password>
            </driver>
            <prepared-statement-cache-size>8</prepared-statement-cache-size>
            <max-connections>20</max-connections>
            <max-idle-time>30s</max-idle-time>
          </database>

when i run this webapp , i got this exception:

java.lang.NullPointerException
    at com.caucho.amber.manager.AmberPersistenceProvider.createEntityManagerFactory(AmberPersistenceProvider.java:65)
    at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:69)
    at com.abc.abc.service.VdcService.exec(VdcService.java:32)
    at com.abc.abc.resources.Apply.apply(Apply.java:55)
    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.sun.jersey.server.impl.model.method.dispatch.AbstractResourceMethodDispatchProvider$TypeOutInvoker._dispatch(AbstractResourceMethodDispatchProvider.java:156)
    at com.sun.jersey.server.impl.model.method.dispatch.ResourceJavaMethodDispatcher.dispatch(ResourceJavaMethodDispatcher.java:67)
    at com.sun.jersey.server.impl.uri.rules.HttpMethodRule.accept(HttpMethodRule.java:208)
    at com.sun.jersey.server.impl.uri.rules.ResourceClassRule.accept(ResourceClassRule.java:75)
    at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:115)
    at com.sun.jersey.server.impl.uri.rules.RootResourceClassesRule.accept(RootResourceClassesRule.java:67)
    at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:724)
    at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:689)
    at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:680)
    at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:324)
    at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:425)
    at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:604)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:91)
    at com.caucho.server.dispatch.ServletFilterChain.doFilter(ServletFilterChain.java:103)
    at org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:416)
    at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:87)
    at org.apache.struts2.dispatcher.ActionContextCleanUp.doFilter(ActionContextCleanUp.java:99)
    at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:87)
    at com.caucho.server.webapp.WebAppFilterChain.doFilter(WebAppFilterChain.java:187)
    at com.caucho.server.dispatch.ServletInvocation.service(ServletInvocation.java:265)
    at com.caucho.server.http.HttpRequest.handleRequest(HttpRequest.java:273)
    at com.caucho.server.port.TcpConnection.run(TcpConnection.java:682)
    at com.caucho.util.ThreadPool$Item.runTasks(ThreadPool.java:743)
    at com.caucho.util.ThreadPool$Item.run(ThreadPool.java:662)
    at java.lang.Thread.run(Thread.java:619)

i can't solve it.How to solve it?help me ,THS