I've got a project of mine in which I would like to take advantage of Hibernate to increase the speed of development for basic operations, combined with Spring's JDBC template to be able to use my own SQL queries for some specific operations and not loose control, since there are some heavy, performance demanding operations.
Is this even possible or a good idea?
Yes, it is possible. And yes, it's a good idea.
The documentation says:
For distributed transactions across multiple Hibernate session factories, simply combine JtaTransactionManager as a transaction strategy with multiple LocalSessionFactoryBean definitions. Each DAO then gets one specific SessionFactory reference passed into its corresponding bean property. If all underlying JDBC data sources are transactional container ones, a business service can demarcate transactions across any number of DAOs and any number of session factories without special regard, as long as it is using JtaTransactionManager as the strategy.
[...]
HibernateTransactionManager can export the Hibernate JDBC Connection to plain JDBC access code, for a specific DataSource. This capability allows for high-level transaction demarcation with mixed Hibernate and JDBC data access completely without JTA, if you are accessing only one database. HibernateTransactionManager automatically exposes the Hibernate transaction as a JDBC transaction if you have set up the passed-in SessionFactory with a DataSource through the dataSource property of the LocalSessionFactoryBean class. Alternatively, you can specify explicitly the DataSource for which the transactions are supposed to be exposed through the dataSource property of the HibernateTransactionManager class.
So, if you're in a full-stack Java EE container supporting JTA transactions and DataSources, use a DataSource defined in your Java EE container and a JTATransactionManager.
If you'e in a simple web container such as Tomcat, use a Spring-provided DataSource and a HibernatTransactionManager.
Related
I was working on a Spring-data-jpa project with spring boot, I see that the creation of repository beans required a datasoure bean to be present, Why is it so?
And can a repository bean be created without datasource bean.
The purpose of a repository is to load and save data into a persistent store.
Spring Data JPA does that using JPA so it needs an EntityManager which in turn need a DataSource.
Strictly speaking the DataSource is only used once the database is actually accessed.
While you definitely nee a DataSource bean you may delay the construction of a normal DataSource by providing a wrapper which instantiates the the actual DataSource at a later point in time.
DelegatingDataSource might be of help, either as a basis class or, since you are going to change the DataSource as a template for an implementation.
See the somewhat related question https://stackoverflow.com/a/61208585/66686
I want to clarify my problem a bit more:
I understand the purposes of using SPring Framework (i.e. container-managed object lifecycle) and also Hibernate (using ORM between Javaobjects and relational database systems - impedance mismatch resolution).
I understand how we autowire an object and Spring takes over the creation and destruction of the object during runtime by looking at the applicationContext.xml file (in addition to persistence.xml file if using Hibernate or any other persistence provider).
What I want to do is the following:
I would like to implement my own shopping service. I already have entity (item) annotated with #Table, #Id, #Column, etc. to tell JPA that this is what will be stored in the database.
I already have a DAO interface (currently only add and delete methods) implemented by a DaoImpl class where I have done the following:
#Repository
#Transactional
public class MyShopDbDaoImpl implements MyShopDbDao {
// The following named unit will be in my persistence.xml file
// Which will be placed in src/main/resources/META-INF folder
#PersistenceContext(unitName="myShopDbDao")
private EntityManager em;
// Getters for em (simply returns em)
// Setters for em (simply assigns an em supplied in the args.)
// Other query method
}
I also have a ShopDbController controller class that uses:
#Autowired
// defined in the applicationContext.xml file
private MyShopDbDao myShopDbDaoImpl
What I am struggling with is the "Understanding" of EntityManagerFactory and EntityManager relationships along with how the transactions must be managed. I know that the following hierarchy is the main starting point to understand this:
Client talks to a controller.
Controller maps the request and gets the entitymanager to do queries and stuff to the database (either a test/local database with JUNIT test etc. or an actual SQL-type database).
What I do know is that transactions can be managed either manually (i.e. beginning, committing, and closing a session) or through Spring container (i.e. using bean defs in applicationContext.xml file). How can I get more information about the entitymanagers and entitymanagerfactory in order to setup my system?
I didn't find the online documentation from Oracle/Spring/Hibernate very helpful. I need an example and the explanation on the relationship between entitymanagerfactory, sessionfactory, entitymanager, and transactionmanager. Could someone please help me with this?
I don't need people to hold my hand, but just put me in a right direction. I have done Spring projects before, but never got to the bottom of some stuff. Any help is appreciated.
EntityManagerFactory will obtain java.sql.Connection objects, through opening/closing new physical connections to the database or using a connection pool (c3p0, bonecp, hikari or whatever implementation you like). After obtaining a Connection, it will use it to create a new EntityManager. The EntityManager can interact with your objects and your database using this Connection and can manage the transaction through calling EntityManager#getTransaction and then calling EntityTransaction#begin, EntityTransaction#commit and EntityTransaction#rollback that internally works with Connection#begin, Connection#commit and Connection#rollback respectively. This is plain vanilla JPA and Spring has nothing to do up to this point.
For transaction management, Spring helps you to avoid opening/closing the transactions manually by using a transaction manager, specifically a class called JpaTransactionManager. This transaction manager will make use of your EntityManagerFactory to open and close a transaction for the EntityManager created for a set of operations. This can be done either using XML configuration or #Transactional annotation on your classes/methods. When using this approach, you won't directly work with your specific classes anymore, instead Spring will create proxies for your classes using cglib and make use of the transaction manager class to open the transaction, call your specific method(s) and execute a commit or rollback at the end, depending on your configuration. Apart of this, Spring provides other configurations like read-only transactions (no data modification operation allowed).
Here's a basic configuration of the elements explained above using Spring/Hibernate/JPA:
<!--
Declare the datasource.
Look for your datasource provider like c3p0 or HikariCP.
Using most basic parameters. It's up to you to tune this config.
-->
<bean id="jpaDataSource"
class="..."
destroy-method="close"
driverClass="${app.jdbc.driverClassName}"
jdbcUrl="${app.jdbc.url}"
user="${app.jdbc.username}"
password="${app.jdbc.password}" />
<!--
Specify the ORM vendor. This is, the framework implementing JPA.
-->
<bean id="hibernateVendor"
class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter"
showSql="false"/>
<!--
Declare the JPA EntityManagerFactory.
Spring provides a class implementation for it.
-->
<bean id="entityManagerFactory"
class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"
persistenceXmlLocation="classpath*:META-INF/persistence.xml"
persistenceUnitName="hibernatePersistenceUnit"
dataSource-ref="jpaDataSource"
jpaVendorAdapter-ref="hibernateVendor"/>
<!--
Declare a transaction manager.
Spring uses the transaction manager on top of EntityManagerFactory.
-->
<bean id="transactionManager"
class="org.springframework.orm.jpa.JpaTransactionManager"
entityManagerFactory-ref="entityManagerFactory"/>
From what i see, your em reference should be a functioning proxy object to your database (this EntityManager is the thing that should be a spring bean, having configured everything, like DB url, driver, etc. Apart from this none of your code should depend on what DB you have). You don't need to know about the classes you mention (entitymanagerfactory sessionfactory transactionmanager). Easy example is:
List<MyBean> bean = (List<MyBean>)em.createNamedQuery("select * from mydb").getResultList();
It should be this easy to run a select * query and get your MyBean typed objects straight ahead, without any explicit conversion by you (this is what hibernate is for).
Similar for insert:
em.persist(myBean);
where myBean is something annotated for Hibernate.
Briefly about transactions, i found best to annotate #Transactional on service METHODS (you did it on a whole dao).
To be very very general:
an entitymanagerfactory is an object responsible of the creation of the entitymanager and it comes from the JPA specifications.
SessionFactory is the hibernate implementation of entitymanagerfactory
session is the hibernate implementation of entitymanager
A transacation manager is an object who manages transaction when you want to define a transaction manually.
So if you want to use hibernate, use SessionFactory and session. And if you want you to stay "generic" use the EntityManagerFactory.
http://www.javabeat.net/jpa-entitymanager-vs-hibernate-sessionfactory/
http://www.theserverside.com/tip/How-to-get-the-Hibernate-Session-from-the-JPA-20-EntityManager
We have an web application under Tomcat, integrated with Hibernate 4X, Spring 4X and HibernateTransactionManager as our transaction manager (currently one MySQL resource).
As part of our configuration distribution, we should integrate with Infinispan as our cache manager to store configuration with other format than in the MySQL. Meaning, not as Hibernate second level cache integration!
I managed to integrate Infinispan with Spring but now I'm facing a big problem due to the fact the MySql transaction and Infinispan must be on the same #Transactional.
I read about Spring JTA and how to integrate with Atomikos (e.g.) as our Global Transaction manager but I'm not sure if we can combine the whole entities to work together and how :(
I need to know if there's an option to work with Atomikos Spring JTA so the Infinispan will recognize this JTA implementation and will handle the MySql and Infinispan as one global transaction! (2PC)
Thanks!
At first I would suggest to configure Spring + Hibernate + JTA together. Here is a very nice tutorial. If you configured everything correctly - you should have one bean of a type TransactionManager. In above tutorial it is configured inside this block:
#Bean(initMethod = "init", destroyMethod = "close")
public TransactionManager transactionManager() throws Throwable {
UserTransactionManager userTransactionManager = new UserTransactionManager();
userTransactionManager.setForceShutdown(false);
return userTransactionManager;
}
Now you may configure Infinispan to use this transaction manager. The easiest way to achieve this, is to implement your own TransactionManagerLookup. This should return the transaction manager, which was created above.
Finally you have to create transactional cache, like this:
<local-cache name="transactional">
<transaction mode="FULL_XA"/>
</local-cache>
After that everything should work with the same Transaction Manager and Spring should handle everything within single #Transactional annotation.
In our project we use Spring and Spring Data (for server side API service), but sometimes we do query not using Spring Data, but using JPA criteria. In order to do so we use:
#PersistenceContext
private EntityManager em;
...
CriteriaBuilder cb = em.getCriteriaBuilder();
...
From the Spring docs:
Although EntityManagerFactory instances are thread-safe, EntityManager instances are not. The injected JPA EntityManager behaves like an EntityManager fetched from an application server's JNDI environment, as defined by the JPA specification. It delegates all calls to the current transactional EntityManager, if any; otherwise, it falls back to a newly created EntityManager per operation, in effect making its usage thread-safe.
So it seems that the way we use should get the current session if exists and if not should create new one. The issue we are facing is a memory leak of this use. seems like this way opens a lot of Hibernate session and does not close them.
So for the question: What is the best practice to getCurrent/open new session in Spring with Hibernate?
Note: HibernateUtil does not have getSessionFactory() as suggested in some other posts
Thanks,
Alon
I went through the Data Access With Spring tutorial and the in memory database they use in step 3 is working. But, I'm not clear on what I need to add/change to get it to query my development (Oracle) database now?
I want to use Hibernate, do I still need this JPAConfiguration class or would I have something Hibernate specific?
Please don't just post a link to the Hibernate reference. I'm reviewing that as well, but since I'm also using Spring, it's not clear to me the proper way to load the hibernate.cfg.xml and inject the Hibernate session in that context.
Don't be blocked by the fact that the class is called JPAConfiguration. You need to understand what the class does. Note that it has the annotation #Configuration which you can use along with AnnotationConfigApplicationContext to produce a Spring bean context.
That functionality is described in the Spring documentation for The IoC container.
What you need to change is how your DataSource and EntityManagerFactory beans are created. You'll need to use a DataSource that gets Connection instances from a JDBC Driver that supports Oracle databases.