I am currently trying to integrate the "open-session-in-view" pattern in my
project (tapestry4 + ejb3).
Both technologies are great, but I get this LazyInitializationException, you
know what I mean.
Inspired by the Seam-approach I tried to do something similar using tapestry
instead of jsf.
My main problem is the handling of "injected" EntityManagers.
EntityManager of type "EXTENDED" are only inherited to other @EJB resources
within a JTA-transaction.
For my understanding the "open-session-in-view" does not need a transaction at
all,
just a open session (=> HibernateSession = EntityManager(EXTENDED)) to prevent
the LazyInitializationException.
But calling an EJB (having a PersistenceContext.TRANSACTION) in the weblayer
without having a JTA-transaction returns detached Entities.
This is correct according to the EJB 3 spec, so I thought about a solution by
using an @Interceptor.
public class ThreadedEntityManagerInterceptor
| {
| private final static ThreadLocal<EntityManager> THREADED_ENTITY_MANAGER
= new ThreadLocal<EntityManager>();
|
| public synchronized static void setEntityManager(EntityManager eMgr)
| {
| THREADED_ENTITY_MANAGER.set(eMgr);
| }
|
| @AroundInvoke
| public Object injectEntityManager(InvocationContext ctx) throws
Exception
| {
| if(THREADED_ENTITY_MANAGER.get() == null)
| {
| return ctx.proceed();
| }
|
| Class cls = ctx.getBean().getClass();
|
| for(Field f : cls.getDeclaredFields())
| {
| if(EntityManager.class.isAssignableFrom(f.getType()))
| {
| if(f.isAnnotationPresent(PersistenceContext.class))
| continue;
|
| if(f.get(ctx.getBean()) == null)
| f.set(ctx.getBean(), THREADED_ENTITY_MANAGER.get());
| }
| }
|
| return ctx.proceed();
| }
| }
"setEntityManager" will be called by a servlet-filter before any EJB is
referenced.
The filter passes in a EntityManager(PersistenceContext.EXTENDED) of a
@Stateful session-bean.
This should work in my opinion.
But calling a method on a EntityManager which is setted by the above
@Intercepter results in the following exception:
Caused by: java.lang.NullPointerException
| at
org.jboss.ejb3.entity.ExtendedEntityManager.getPersistenceContext(ExtendedEntityManager.java:59)
| at
org.jboss.ejb3.entity.ExtendedEntityManager.find(ExtendedEntityManager.java:114)
| at
de.jitek.component.friendler.EntityServiceBean.findByPrimaryKey(EntityServiceBean.java:32)
| 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:585)
| at
org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:109)
| at
org.jboss.ejb3.interceptor.InvocationContextImpl.proceed(InvocationContextImpl.java:168)
| at
de.jitek.component.friendler.ThreadedEntityManagerInterceptor.injectEntityManager(ThreadedEntityManagerInterceptor.java:57)
| 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:585)
| at
org.jboss.ejb3.interceptor.InvocationContextImpl.proceed(InvocationContextImpl.java:120)
| at
org.jboss.ejb3.interceptor.EJB3InterceptorsInterceptor.invoke(EJB3InterceptorsInterceptor.java:62)
| at
org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:98)
| at
org.jboss.ejb3.AllowedOperationsInterceptor.invoke(AllowedOperationsInterceptor.java:47)
| at
org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:98)
| at
org.jboss.aspects.tx.TxPolicy.invokeInCallerTx(TxPolicy.java:126)
Would be great if someone could explain why this happen and how to solve the
problem.
Is it possible at all, what I am trying to do or is there already an existing
solution of the LazyInitializationException (tapestry + ejb3) ?
Any help would very appreciated.
Regards,
Jan
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