Facing this kind of choice recently, I looked into possible migration paths between the two variants. One thing I have seen often on Seam 2 applications is that people really like the Hibernate criteria API and therefore use Hibernate directly. While Hibernate is an excellent ORM framework, it’s preferrable to use the JPA API when moving to Java EE 6. So - why not use Seam 2 with JPA 2, which finally features an even better (typesafe) criteria API?
It turns out to be a quite easy setup (once you get classloading right), with some small extra modifications. I’ve been using Maven, Seam 2.2 and Hibernate 3.5.4 on JBoss 4.2.3. Lets start with preparing the server. You need to remove the old Hibernate and JPA classes and add the new persistence provider with some dependencies (of course this will be different on other servers):
To be removed from server/lib:
Add to server/lib:
Next lets create a sample Seam project. I’m using the CTP Maven archetype for Seam. In the POM file, remove the references to the Hibernate and old JPA libraries and add the new JPA 2 libraries:
<!-- Remove all embedded dependencies
<dependency>
<groupId>org.jboss.seam.embedded</groupId>
<artifactId>...</artifactId>
</dependency -->
<dependency>
<groupId>org.hibernate.javax.persistence</groupId>
<artifactId>hibernate-jpa-2.0-api</artifactId>
<version>1.0.0.Final</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-core</artifactId>
<version>3.5.4-Final</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-jpamodelgen</artifactId>
<version>1.0.0.Final</version>
<scope>provided</scope>
</dependency>
Note: If you’ve been using embedded JBoss for your integration tests, this will probably not work without exchanging the JARS there too. I’ve been moving away from this approach as it turned out to be a common reason for headache on our nightly builds as well as running tests in Eclipse. I’m very excited to see Arquillian evolving on this topic!
JPA 2 integrates with JSR 303 bean validation, which is the successor of Hibernate Validator. Unfortunately Seam 2 has references to Hibernate Validator 3, where JPA needs version 4. Adding the validator legacy JAR fixes this problem. As bean validation is now part of Java EE 6, we can add it to the server classpath as shown above, as well as to our POM:
<dependency>
<artifactId>validation-api</artifactId>
<groupId>javax.validation</groupId>
<version>1.0.0.GA</version>
<scope>provided</scope>
</dependency>
Now it’s time to move to some code. You can jump straight in your persistence config files and bring the schema up to version 2:
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
version="2.0"> ...
<entity-mappings xmlns="http://java.sun.com/xml/ns/persistence/orm"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence/orm http://java.sun.com/xml/ns/persistence/orm_2_0.xsd"
version="2.0"> ...
Seam proxies entity managers to implement features like EL replacements in JPQL queries. This proxy does not implement methods new in JPA 2 and will therefore fail. You can write your own proxy very easy:
public class Jpa2EntityManagerProxy implements EntityManager {
private EntityManager delegate;
public Jpa2EntityManagerProxy(EntityManager entityManager) {
this.delegate = entityManager;
}
@Override
public Object getDelegate() {
return PersistenceProvider.instance()
.proxyDelegate(delegate.getDelegate());
}
@Override
public void persist(Object entity) {
delegate.persist(entity);
}
...
}
Add the special Seam functionality as needed. In order to use the proxy with Seam, you’ll have to overwrite the HibernatePersistenceProvider Seam component:
@Name("org.jboss.seam.persistence.persistenceProvider")
@Scope(ScopeType.STATELESS)
@BypassInterceptors
// The original component is precedence FRAMEWORK
@Install(precedence = Install.APPLICATION,
classDependencies={"org.hibernate.Session",
"javax.persistence.EntityManager"})
public class HibernateJpa2PersistenceProvider extends HibernatePersistenceProvider {
@Override
public EntityManager proxyEntityManager(EntityManager entityManager) {
return new Jpa2EntityManagerProxy(entityManager);
}
}
If you use Hibernate Search, have a look at the superclass implementation - you might want to instantiate a FullTextEntityManager directly (as you have it in your classpath - but note that this has not been tested here).
Both implementations are on our Google Code repository, and you can integrate them directly over the following Maven dependency:
<dependency>
<groupId>com.ctp.seam</groupId>
<artifactId>seam-jpa2</artifactId>
<version>1.0.0</version>
</dependency>
You’re now ready to code JPA 2 queries! We’ve already included the meta model generator utility, so let’s activate it for the build:
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>build-helper-maven-plugin</artifactId>
<executions>
<execution>
<id>add-source</id>
<phase>validate</phase>
<goals>
<goal>add-source</goal>
</goals>
<configuration>
<sources>
<source>${basedir}/src/main/hot</source>
<source>${basedir}/target/metamodel</source>
</sources>
</configuration>
</execution>
</executions>
</plugin>
<plugin>
<groupId>org.bsc.maven</groupId>
<artifactId>maven-processor-plugin</artifactId>
<version>1.3.1</version>
<executions>
<execution>
<id>process</id>
<goals>
<goal>process</goal>
</goals>
<phase>generate-sources</phase>
<configuration>
<outputDirectory>${basedir}/target/metamodel</outputDirectory>
<processors>
<processor>
org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor
</processor>
</processors>
</configuration>
</execution>
</executions>
</plugin>
In order to use the processor plugin, you also need the following Maven repositories in your POM:
<pluginRepository>
<id>annotation-processing-repository</id>
<name>Annotation Processing Repository</name>
<url>http://maven-annotation-plugin.googlecode.com/svn/trunk/mavenrepo</url>
</pluginRepository>
<pluginRepository>
<id>jfrog-repository</id>
<name>JFrog Releases Repository</name>
<url>http://repo.jfrog.org/artifactory/plugins-releases</url>
</pluginRepository>
Run the build, update the project config to include the new source folder - and finally we’re ready for some sample code:
@Name("userDao")
@AutoCreate
public class UserDao {
@In
private EntityManager entityManager;
private ParameterExpression<String> param;
private CriteriaQuery<User> query;
@Create
public void init() {
CriteriaBuilder cb = entityManager.getCriteriaBuilder();
query = cb.createQuery(User.class);
param = cb.parameter(String.class);
Root<User> user = query.from(User.class);
query.select(user)
.where(cb.equal(user.get(User_.username), param));
}
public User lookupUser(String username) {
return entityManager.createQuery(query)
.setParameter(param, username)
.getSingleResult();
}
}
This is now quite close to Java EE 6 code - all we will have to do is exchange some annotations:
@Stateful
public class UserDao {
@PersistenceContext
private EntityManager entityManager; ...
@Inject
public void init() { ...
}
Enjoy!
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