Entitymanager is null when inject by glassfish - ejb-3.0

Question

*when i deploy project in glassfish entitymanager is null.if i use another thing instead of RPC like servlet project work probably *
session bean is:
#Stateless
public class logic implements logicLocal {
#PersistenceContext(unitName="T2PU")
private EntityManager em;
#Override
public void addToDB(Test t){
em.persist(t);
}
}
and GWT RPC is :
public class MainRPCImpl extends RemoteServiceServlet implements MainRPC {
#EJB
logicLocal logic;
#Override
public String addToDB(Test t) {
String m="fail";
try {
logic.addToDB(t);
m="done successfuly";
} catch (Exception e) {
return m;
}
return m;
}
}
persistence unit is :
<persistence-unit name="T2PU" transaction-type="JTA">
<jta-data-source>acm</jta-data-source>
<exclude-unlisted-classes>false</exclude-unlisted-classes>
<properties/>
</persistence-unit>
</persistence>
and glassfish-resources
<resources>
<jdbc-connection-pool allow-non-component-callers="false" associate-with-thread="false" connection-creation-retry-attempts="0" connection-creation-retry-interval-in-seconds="10" connection-leak-reclaim="false" connection-leak-timeout-in-seconds="0" connection-validation-method="auto-commit" datasource-classname="com.mysql.jdbc.jdbc2.optional.MysqlDataSource" fail-all-connections="false" idle-timeout-in-seconds="300" is-connection-validation-required="false" is-isolation-level-guaranteed="true" lazy-connection-association="false" lazy-connection-enlistment="false" match-connections="false" max-connection-usage-count="0" max-pool-size="32" max-wait-time-in-millis="60000" name="mysql_acm_rootPool" non-transactional-connections="false" pool-resize-quantity="2" res-type="javax.sql.DataSource" statement-timeout-in-seconds="-1" steady-pool-size="8" validate-atmost-once-period-in-seconds="0" wrap-jdbc-objects="false">
<property name="serverName" value="localhost"/>
<property name="portNumber" value="3306"/>
<property name="databaseName" value="acm"/>
<property name="User" value="root"/>
<property name="Password" value="1234"/>
<property name="URL" value="jdbc:mysql://localhost:3306/acm"/>
<property name="driverClass" value="com.mysql.jdbc.Driver"/>
</jdbc-connection-pool>
<jdbc-resource enabled="true" jndi-name="acm" object-type="user" pool-name="mysql_acm_rootPool"/>
</resources>
specially thanks in advance.

Answer 1

Maybe there are different reasons, but don't you need to use the jdbc context prefix for your JNDI name in persistence.xml? Something like this:
<jta-data-source>jdbc/acm</jta-data-source>
From the Glassfish administration guide:
A JDBC resource is created by specifying the connection pool with
which the resource will be associated . Use a unique Java Naming and
Directory Interface (JNDI) name to identify the resource. ... Because
all JNDI names are in the java:comp/env subcontext, when specifying
the JNDI name of a JDBC resource in the Administration Console, use
only the jdbc/name format.