Data Access Layer is not responsible for transaction management am I correct? I have these DAO implementations: HibernateDAO and SqlDAO. If I will choose Hibernate and handle its transaction management at above layer, when I switch to SQL then I will change every single transaction management made by the Hibernate to SQL? This is bad right? What strategy will I gonna use in this case? TIA.
I've never worked on transactions outside of spring and JTA. Spring offers a transactions across several different platforms using transactions. You may want to check that out.
Also, I've seen JTA transactions work on ejb, Hibernate and Jms messages, but not sure if it will work for jdbc and hibernate, more on hibernate transactions here.
Related
I am using hibernate for the REST API. Right now all the transactions are handled by explicitly calling beginTransaction and transaction.commit. The transaction is rolled back in case of a failure. I am looking to use #Transactional instead of all the beginTransactions and commit transactions. Could someone tell me how can I integrate #Transactional in my hibernate. I am using mysql for querying the database.
You can annotate your query method with #Transactional so you get your transaction opened, commited and closed when your method ends.
Be careful about isolation levels (https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/transaction/annotation/Transactional.html#isolation--) because it indicates when Spring will create a new session for your transaction, or simply use already opened one.
When you thrown an exception on your method, transaction gets an automatic rollback and you're good :)
You can use Spring Framework with Hibernate Integration. The advantage is spring manages the Hibernate session's and all the low level things that we have to manage manually in hibernate like granular commit etc. Here is the example of this. this is older repository so uses older version of Spring and Hibernate but you can upgrade it here
In my standalone java application, jms and hibernate are used for fulfilling my requirements. I used the JTA transaction manager for the transaction management purposes. Can i enlist the XAResource for the hibernate and jms in the jta transaction to ensure the atomicity of my application.
Yes, it's possible. Called sometimes two-phase commit, it synchronises transactions between multiple resources.
First of all make sure you're RDBMS supports and has the feature turned on. In PostgreSQL, for example, this means setting the max_prepared_transactions configuration parameter from postgresql.conf to something above 0.
Also, make sure the JMS queue you're using support this transaction method. In Wildfly this means adding transaction="xa" on pooled-connection-factory.
Is it good practice to have interceptors to manage transactions?
I have a strong point though that it is equivalent to begin and commit in the action itself.
Why should I use interceptor managed transactions at all?
It's not bad practice, for example Spring framework uses aspects for 'auto-begin' and 'auto-commit' transactions using #Transactional annotation.
Why should I use interceptor managed transactions at all?
It reduces a lot of boilerplate code: opening connection, beginning transaction, committing transaction and closing connection.
But if you want to write your own transaction manager using interceptors - beware of concurrency issues
According to image you posted:
It's better not to expose transaction management from Service layer. It's better if your presentation layer don't know anything about Transaction management. So try to encapsulate your transaction management code in service layer or in DAO layer. If your presentation layer manages transaction and service layer is not, it's mean your services is not self-contained, and they can be reused by other client only if client provide some transaction management logic.
From Comments:
Better is to put transaction management code to service layer, because
service layer usually performs some business level operations, which
must be performed within one transaction. So your service method can
use 2 or more DAOs to perform all DB operations in one transaction.
Sorry, there is no links - I tell it your from my experience.
I am loading a large set of data into a database from a webservice. I am using eclipslink for persistence and running the application on glassfish 3.0. I run into problems on my test data set in that there are a few foreign key constraint violations. I am fine with the violation, I do not want that data if it is not complete. My problem however comes in that the exception is thrown in the container. That then marks my transaction for a rollback, and I get no data at all then.
I would like to continue using JTA but am not sure if I can do what I want to achieve, and that is create my own JTA transaction so I can control when it commits,etc. I am not sure if that is a good idea though as I feel by doing so I may be destroying some of the benefits of using JTA.
So is it possible to get a JTA transaction?
Do the database work in a method of a session bean. Annotate that method with:
#TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
It will be given its own transaction. The outer transaction will be suspended while it does its stuff.
http://wiki.eclipse.org/Using_Advanced_Unit_of_Work_API_%28ELUG%29#Integrating_the_Unit_of_Work_with_an_External_Transaction_Servicestrong text**
Read How to Acquire a Unit of Work with an External Transaction Service. Apparently you can snatch the UserTransaction and/or start your own by querying the container JNDI for UserTransaction
I wan to know how the transaction is internally implemented in EJB. I want to know the logic they use to create a transaction. if you could point out some articles that would be helpful
Hibernate doesn't implement transactions, it relies on and wraps JDBC transactions or JTA transactions (either container managed or application managed).
Regarding EJBs, if you want to understand the details of a JTA Transaction Manager, you'll need to be fluent with the JTA interfaces UserTransaction, TransactionManager, and XAResource which are described in the JTA specification. The JDBC API Tutorial and Reference, Third Edition will also be useful to understand the XA part of a JDBC driver.
Then, get the sources of an EJB container (like JBoss) or of a standalone JTA Transaction Manager (like Atomikos) to analyze the TM part. And good luck.
This question could have answers at many levels.
A general discussion of what's going on can be found here
My summary goes like this ... First, somewhere there must be a transaction coordinator, the EJB container will know about the coordinator - typically that's part of the application server. So all the EJB container has to do is to call
someobject.BeginTransaction()
that's it. The actual API the EJB container uses is JTA. EJBs can actually use Bean Managed transaction transaction or Container managed transactions. In the Bean Managed case the implementer nhas to make the JTA calls. More usually we use Container Managed transactions (CMT). In which case the container has logic which is run before the implementation is reached. For example:
if ( we're not already in a transaction )
begin transaction
call the EJB implementation
and later the container has logic
if ( finished processing request )
commit transaction
with other paths to abort the transaction if errors have happened.
Now that logic is more complex because CMT EJBs are annotated with transaction control statements. For example you can say things "if we already have a transaction, use it" So if one EJB calls another only a single transaction is used. Read up the EJB spec for that.
However all that's pretty obvious in any write-up of Java EE EJBs. So I suspect that you're asking moe about what happens inside the JTA calls, how the transaction manager is implemented and its relationship to the transactional resource managers (eg. Databases). That's a huge topic. You've actually go implementations of the XA distributed transaction protocol down there. Frankly I doubt that you really need to need to know this. At some point you have trust the APIs you're using. However there is one key detail: your Transaction Manager (typically the App Server itself) must be able to tell the REsource Managers the fate of any given transaction, and that information must survive restart of the App Server, hence some persistent store of transaction information must be kept. You will find transaction logs somewhere, and in setting up the App Server you need to make sure those logs are well looked after.
From EJB in Action book
The protocol commonly used to achieve multiple resource is the two-phase commit. The two-phase commit protocol performs an additional preparatory step before the final commit. Each resource manager involved is asked if the current transaction can be successfully committed. If any of the resource managers indicate that the transaction cannot be committed if attempted, the entire transaction is abandoned (rolled back). Otherwise, the transaction is allowed to proceed and all resource managers are asked to commit.
A resource manager can be a database, for instance. Others examples includes a Message Service. The component which coordinates transactions is called Transaction manager.
Suppose you have an application which involves two distincts databases. How does Transaction manager performs its work by using Two phase commit protocol ?
Transaction Manager ask database 1 if it can commit the current transaction
If so, ask database 2 if it can commit the current transaction
Transaction Manager ask database 1 to commit
Transaction Manager ask database 2 to commit
Hibernate is built on top of the JDBC API. It just coordinates one database. So if you call
session.commit();
Behind the scenes, it call
connection.commit();
If you really want to study Transaction internals, my advice is Java Transaction Processing book.
Hibernate has TransactionFactory:
An abstract factory for Transaction instances. Concrete implementations are specified by hibernate.transaction.factory_class.
It has implementations: JDBCTransactionFactory, JTATransactionFactory, CMTTransactionFactory. These factories create an instance of Transaction - for example JDBCTransaction.
Then I can't tell you what happens for JTA and CMT, but for JDBC it's as simple as setting the auto-commit to false (when you call begin a transaction):
connection.setAutoCommit(false);
And respectively on transaction.commit(): connection.commit()
If any exception occurs when operating with the session, it invokes connection.rollback()
Another good read would be the JTS articles by Brian Goetz; links:
http://www.ibm.com/developerworks/java/library/j-jtp0305.html
http://www.ibm.com/developerworks/java/library/j-jtp0410/index.html
http://www.ibm.com/developerworks/java/library/j-jtp0514.html