PersistenceContext and EntityManager

[rmic]

Hi everybody,

I've got a problem with this "magical" @PersistenceContext... It doesn't inject any EntityManager :( ... my entityManager variable always evaluates to null and generates an horrible NullPointerException...

I already googled for hours to find a solution and the only thing I found was about using an EntityManagerFactory which also had to be injected and which stayed to the "null" value as well...

Does anybody knows something about that ?

Thanks in advance !

rmic.

[wauwau0977]

hi

hard to say what your mistake is. for me it works. see the trailblazer from jboss which is very helpful and up-to-date:
http://trailblazer.demo.jboss.com/EJB3Trail/

the basic idea if you are using your own datasource is about that

1) code incetion:

@PersistenceContext(unitName = "YourEntityManagerName")

2) a persistence.xml in metainf about like this:

<persistence>
 <persistence-unit name="YourEntityManagerName">
 <jta-data-source>java:/OpenPaintingDSMySql</jta-data-source>
 <properties>
 <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect"/>
 <property name="hibernate.cache.provider_class" value="org.jboss.ejb3.entity.TreeCacheProviderHook"/>
 <property name="hibernate.treecache.mbean.object_name" value="jboss.cache:service=EJB3EntityTreeCache"/>
 <property name="hibernate.hbm2ddl.auto" value="update"/>
 </properties>
 </persistence-unit>
</persistence>

3) define your datasource in the deploy folder of the server

<?xml version="1.0" encoding="UTF-8"?>
<!-- this file goes to server/xxx/deploy -->
<datasources>
 <local-tx-datasource>

 <jndi-name>OpenPaintingDSMySql</jndi-name>
 <connection-url>jdbc:mysql://localhost:3306/openpainting</connection-url>
 <driver-class>com.mysql.jdbc.Driver</driver-class>
 <user-name>xxxx</user-name>
 <password>yyyy</password>

 <min-pool-size>2</min-pool-size>
 <max-pool-size>20</max-pool-size>
 <idle-timeout-minutes>5</idle-timeout-minutes>

 <exception-sorter-class-name>com.mysql.jdbc.integration.jboss.ExtendedMysqlExceptionSorter</exception-sorter-class-name>
 <valid-connection-checker-class-name>
 com.mysql.jdbc.integration.jboss.MysqlValidConnectionChecker</valid-connection-checker-class-name>

 </local-tx-datasource>
</datasources>

but as mentioned... check out the tutorial, they did a very well job

regards,
patrick

--
patrick heusser
http://www.x8ing.com/fractal/

[rmic]

Thanks for your answer...

I certainly missed something... The tutorial is really well done, but all they tell about using the entity manager is only that it should be preceded by the @PersistenceContext annotation.

This is what my code looks like...

public class Mediastore implements Serializable {
 @PersistenceContext(unitName="mediastore")
 private EntityManager entityManager ;
 private String hello = "Hello World";

 private static final long serialVersionUID = -2416336874715455139L;

 @SuppressWarnings("unchecked")
 public Mediastore(){

 if(entityManager != null){
 System.out.println("Entity manager created successfully");
 }
 else {
 System.out.println("Entity Manager is null !");
 }

This is the code which helped me to say that the EntityManaged was not injected correctly, after having had a lot of null pointer exceptions...

Here's my persistence.xml file :

<persistence>
 <persistence-unit name="mediastore">
 <jta-data-source>java:/mediastoreDS</jta-data-source>
 <properties>
 <property name="hibernate.hbm2ddl.auto" value="create-drop"/>
 <property name="hibernate.cache.use_query_cache" value="true"/>
 <property name="hibernate.show_sql" value="true"/>
 </properties>
 </persistence-unit>
</persistence>

My "mediastore-ds.xml" file :

<?xml version="1.0" encoding="UTF-8"?>

<datasources>
 <local-tx-datasource>
 <jndi-name>mediastoreDS</jndi-name>
 <connection-url>jdbc:postgresql://localhost/mediastore</connection-url>
 <driver-class>org.postgresql.Driver</driver-class>
 <user-name>postgres</user-name>
 <password>postgres</password>
 <min-pool-size>5</min-pool-size>
 <max-pool-size>20</max-pool-size>
 <idle-timeout-minutes>10</idle-timeout-minutes>
 <track-statements>true</track-statements>
 </local-tx-datasource>
</datasources>

My ear file is packaged like this :

mediastore.ear
 /META-INF
 application.xml
 mediastore.jar
 /META-INF
 persistence.xml
 /packages/classfiles

 mediastore.war
 /WEB-INF
 web.xml
 faces-config.xml
 /lib
 jarfiles
 /classes
 packages/classes
 index.jsp
 home.jsp

I hope this could help someone to see what I did wrong.

Thanks in advance,

rmic.

[rmic]

In fact, I think I'm really doing something wrong ... the @EJB annotation doesn't work either ...

[bluevervet]

Hi rmic

I have come across exactly the same problem. Not sure whether it's us, JBoss or Hibernate.

Have you been able to shed any light on this yet?

Thanks
dh

[elponderador]

If you are relying on the debug messages you are printing out in the constructor that is your problem, since the values are injected AFTER the object is constructed.

[holeinone]

First: Your answer did the trick,Thanks a lot!
secondly: WHY?
Why is injection done AFTER the constructor? I made those nice final fields to be injected and now they fail ;-(

[alrubinger]

Why is injection done AFTER the constructor?

How is it possible to inject values into an object *before* the object itself has been created?

S,
ALR