Wednesday 13 August 2014


When connecting to a database a transaction is often required.  There are a number of ways of doing this but the most common is to use Spring transactions.


This dependency is needed to allow transactions


Spring Context

In the spring configuration an entity manager is necessary (see Entity Manager blog entry)

<tx:annotation-driven transaction-manager="transactionManager" proxy-target-class="true" />

<!-- Define a transaction manager so that the @TransactionConfiguration and @Transactional can be used -->
<bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
<property name="entityManagerFactory" ref="entityManagerFactory" />

Proxy Class

The above combination will allow spring to create proxy classes which create a transaction before passing into the @Transactional method.  This means that because it is a proxy @Transactional doesn't work for any 'internal' call within the your class.  Eg even if a method is public if it is called from within the same class it won't pass through the proxy and therefore won't have a transaction.
If this type of behaviour is required then the transactions can be wired using AOP and the transaction code is created at compile time rather than a runtime proxy.

Exception Handling

Normal exceptions can be caught using the normal try - catch but if the database isn't there at all then there is an exception generated in the proxy before the method code is called.  The exception is a 

To catch the exception within the same method as the actual database errors the transaction can be created a different way.

Programmatic Transactions

A programmatic transaction can be created using the TransactionTemplate in which case the TransactionException (CannotCreateTransactionException) can be caught in the same place.

        transactionTemplate.execute(new TransactionCallbackWithoutResult()
            protected void doInTransactionWithoutResult(final TransactionStatus status)
                 // Do something to the database here
    catch (PersistenceException | TransactionException e)
        LOG.error("Database Error", e);

There is also a TransactionCallback() which returns the object from the database whereas the one above doesn't do that.

The transactionTemplate can be created in spring configuration,

    <property name="transactionTemplate">
        <bean class="">
            <constructor-arg ref="transactionManager" />

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