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Force spring to use only one connection for transaction

I have a spring (version 3.2.15) application that uses more than one connection in a transactional method.
My use case is:
Call to transactional method (which opens one connection)
Query for an entity (which opens and closes another connection)
Persist the entity
End of the method (closes the first connection)
The problem is that I have a limited number of connections, and I need to ensure that only one connection is used per transactional method. This problem causes a dead lock in my application because there are much more transactions opened than the number of connections available.
Is there any way that I can use the same connection spring uses to maintain the transaction on my method? I have already tried the hibernate option hibernate.connection.release_mode in after_statement mode, but an error occurs when hibernate is trying to commit the transaction. 
I've read the spring transaction documentation but I cannot figure out how to configure spring to behave this way.

JDBC RollBack After Connection Close

Say a connection is opened and auto commit is set to false to start a transaction. After the transaction is complete, I would like to rollback any changes to bring the database to the state it was before I started the transaction.
My problem is, that during the transaction the connection is closed, and thus all the changes are committed at that time.
Is there a way to rollback the state of the database to before the initial transaction started?
and yes I've tried using Savepoints to no avail.

This really depends on what you're doing, why and how.
If you have a reference to the transaction, you can rollback yourself.
If not, can you throw an exception at the end?
If all you want is to test things, why not use an embedded DB like H2 and start from scratch each time?
If H2 doesn't cut it, check out testcontainers.

Transaction Management in EJB

Recently I was asked a question which left me thinking..want to get the community views on the same question.
I have a CustomerEJB which has say a createCustomer method. My EJB is exposed as a web service and hence createCustomer is one of its operations.
When a request hits createCustomer, 2 operations need to be performed
An INSERT SQL query into the database which may be adding certain data into db that came in input request
creation of a text file, say .txt in the file system.
Now the question is I want to couple these two tasks into a transaction. If any one task fails, I rollback the other task as well.
Without mentioning any hot technologies, like Spring/Hibernate what is the approach I can follow for Transaction management
My thoughts:
1. I can use JTA, demarcate the transaction boundaries and perform commit and rollback accordingly. JDBC can be used for the SQL task
2. I can use DAOs
Inviting your kind suggestions/comments

You would need to wrap the file creating in a XA capable JCA connector (not sure whether there's a ready made one out there, a quick good only found this fsconnector which doesn't support transactions yet), and use an XA driver for your DB transaction (most DBs will will be able handle this) and then wrap your EJB in an XA transaction (should be straightforward).
As long as both resources can handle the XA transactions, you'll get the benefit of 2-phase commits, which is what you're after.

How to debug transaction commit in sybase?

I have a transaction based application and it rolls the operation back on an error. However
in some cases, the rollback doesn't happen. ( Though its getting called from the application). Ours is a very complex application and there are chances that some code is directly committing the data. Is there a way to debug the commit to the database? (Either from java or from the database?). From java, we are not able to do this because, java.sql.Connection is an interface and the implementation is provided by sybase jconnect for which we don't have the source.

I am not sure this will help, but with this driver, this helps in tracing all the DML operations you perform on the database including commit & rollback. When you use p6spy
it logs every database hit into a log file, from where you can easily figure out where your application is performing a commit.
Apart from the above suggestion, I fell every database comes with some sort of monitoring tools, which with you can monitor which DML is fired within a span of time.

Viewing Data From Transactional Tests - Hibernate + Spring + MySQL

I have a bunch of tests in a Hibernate/Spring application. Yesterday, I transitioned them from using the JUnit 3.8 base test class provided by Spring to the JUnit 4.4 one.
Everything works great, because now, my tests are wrapped in transactions, and data created/modified is automatically rolled back (instead of me writing code to delete newly-created entities).
The only problem is that I cannot peek into the database during test execution. If a test fails, I often add breakpoints near the end and peer into the MySQL database via SQL Yog to see what's going on. But now, I just see empty tables. (I mean in integration tests that simulate production very closely and actually touch the database.)
I tried setting the global isolation level to read uncommitted, but it didn't change the fact that I can't see the data. How can I configure Spring/Hibernate to allow me to view the data from another process?

I had the same issue, and found that setting the session isolation level while using YOG sometimes helped.
SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
This only uncovered another disturbing issue - while running tests, the Hibernate didn't actually run some of the actions unless I used HibernateTemplate.flush(); after every Hibernate operation.
As this very annoying, I finally set Hibernate so it would always flush queries, like this:
HibernateTemplate hibernateTemplate;
...
hibernateTemplate.setFlushMode(HibernateTemplate.FLUSH_ALWAYS);