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https://issues.apache.org/struts/browse/WW-1399?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_42823
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ahardy66 edited comment on WW-1399 at 12/23/07 10:29 AM:
-----------------------------------------------------------
Simplified my previous entry
The following is a servlet filter written for the most stripped-down,
standards-compliant JPA implementation that I can currently reasonably put
together. It's probably too specific to my requirements to be any use, but here
it is anyway.
The DAOs retrieve the same entity manager every time by calling ContextManager.
I don't use the Spring DAO component. Any call to
EntityManagerFactory.createEntityManager() from the same thread will retrieve
the same EntityManager - this is in the JPA spec. See section 5.2.
This is only for the extended persistence context paradigm - I haven't looked
at implementing it in container with JEE transactions.
public class OpenEntityManagerInViewFilter implements Filter
{
public final void doFilter(ServletRequest request,
ServletResponse response, FilterChain filterChain)
throws ServletException, IOException
{
ContextManager.init();
EntityManager entityManager = ContextManager.getEntityManager();
try
{
filterChain.doFilter(request, response);
}
finally
{
ContextManager.closeEntityManager();
}
}
public void destroy()
{
}
public void init(FilterConfig newArg0) throws ServletException
{
}
}
public class ContextManager
{
private static EntityManagerFactory entityManagerFactory;
private static ThreadLocal<EntityManager> entityManagerThreadLocal =
new ThreadLocal<EntityManager>();
public static synchronized init()
{
if (entityManagerFactory == null)
{
entityManagerFactory =
Persistence.createEntityManagerFactory("myPersistenceUnit",
getJpaParameters());
}
}
public static EntityManager getEntityManager()
{
EntityManager entityManager = entityManagerThreadLocal.get();
if (entityManager == null)
{
entityManager = entityManagerFactory.createEntityManager();
entityManagerThreadLocal.set(entityManager);
}
return entityManager;
}
public static void closeEntityManager()
{
EntityManager entityManager = entityManagerThreadLocal.get();
if (entityManager != null && entityManager.isOpen())
{
entityManager.close();
}
// dump reference to EntityManager
entityManagerThreadLocal.remove();
}
}
NB For transaction management by the Spring Framework, the Spring context
config sets up a transaction manager using
org.springframework.orm.jpa.JpaTransactionManager which takes the
EntityManagerFactory as a constructor parameter, using the ContextManager as
the factory bean:
<bean id="transactionManager"
class="org.springframework.orm.jpa.JpaTransactionManager">
<property name="entityManagerFactory">
<bean class="org.permacode.ContextManager"
factory-method="getEntityManagerFactory" />
</property>
</bean>
NB The method getJpaParameters() is superfluous if all the parameters are in
the persistence.xml.
NB I stripped down this version here because the code as I have it in my app
only initializes JPA on a just-in-time basis, i.e. if null, initialize. For
this reason I have a lot of checks in the close-down methods to make it
shutdown gracefully from any state.
was (Author: ahardy66):
Simplified my previous entry
The following is a servlet filter written for the most stripped-down,
standards-compliant JPA implementation that I can currently reasonably put
together. It's probably too specific to my requirements to be any use, but here
it is anyway.
For transaction management by the Spring Framework, the Spring context config
sets up a transaction manager using
org.springframework.orm.jpa.JpaTransactionManager which takes the
EntityManagerFactory as a constructor parameter.
The DAOs can retrieve the same entity manager that Spring is given. (I don't
use the Spring DAO component.) Any call to
EntityManagerFactory.createEntityManager() from the same thread will retrieve
the same EntityManager - this is in the JPA spec. See section 5.2.
This is only for the extended persistence context paradigm - I haven't looked
at implementing it in container with JEE transactions.
public class OpenEntityManagerInViewFilter implements Filter
{
public final void doFilter(ServletRequest request,
ServletResponse response, FilterChain filterChain)
throws ServletException, IOException
{
EntityManagerFactory entityManagerFactory =
ContextManager.getEntityManagerFactory();
EntityManager entityManager = ContextManager.getEntityManager();
try
{
filterChain.doFilter(request, response);
}
finally
{
ContextManager.closeEntityManager();
}
}
public void destroy()
{
}
public void init(FilterConfig newArg0) throws ServletException
{
}
}
public class ContextManager
{
private static ThreadLocal<EntityManager> entityManagerThreadLocal =
new ThreadLocal<EntityManager>();
public static EntityManager getEntityManager()
{
EntityManager entityManager = entityManagerThreadLocal.get();
if (entityManager == null)
{
EntityManagerFactory entityManagerFactory =
Persistence.createEntityManagerFactory("myPersistenceUnit",
getJpaParameters());
entityManager = entityManagerFactory.createEntityManager();
entityManagerThreadLocal.set(entityManager);
}
return entityManager;
}
public static void closeEntityManager()
{
EntityManager entityManager = entityManagerThreadLocal.get();
if (entityManager != null && entityManager.isOpen())
{
entityManager.close();
}
// dump reference to EntityManager
entityManagerThreadLocal.remove();
}
}
> MailReader - Migrate to JPA and Derby
> -------------------------------------
>
> Key: WW-1399
> URL: https://issues.apache.org/struts/browse/WW-1399
> Project: Struts 2
> Issue Type: Improvement
> Components: Example Applications
> Reporter: Ted Husted
> Assignee: Ted Husted
> Priority: Minor
> Fix For: 2.1.x
>
>
> The in-memory XML database used by the MailReader is interesting, but a
> best-practices example that used the JPA and a SQL DBMS would be more
> instructive.
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