[[transaction-programmatic]]
= Programmatic Transaction Management

The Spring Framework provides two means of programmatic transaction management, by using:

* The `TransactionTemplate` or `TransactionalOperator`.
* A `TransactionManager` implementation directly.

The Spring team generally recommends the `TransactionTemplate` for programmatic
transaction management in imperative flows and `TransactionalOperator` for reactive code.
The second approach is similar to using the JTA `UserTransaction` API, although exception
handling is less cumbersome.


[[tx-prog-template]]
== Using the `TransactionTemplate`

The `TransactionTemplate` adopts the same approach as other Spring templates, such as
the `JdbcTemplate`. It uses a callback approach (to free application code from having to
do the boilerplate acquisition and release transactional resources) and results in
code that is intention driven, in that your code focuses solely on what
you want to do.

NOTE: As the examples that follow show, using the `TransactionTemplate` absolutely
couples you to Spring's transaction infrastructure and APIs. Whether or not programmatic
transaction management is suitable for your development needs is a decision that you
have to make yourself.

Application code that must run in a transactional context and that explicitly uses the
`TransactionTemplate` resembles the next example. You, as an application
developer, can write a `TransactionCallback` implementation (typically expressed as an
anonymous inner class) that contains the code that you need to run in the context of
a transaction. You can then pass an instance of your custom `TransactionCallback` to the
`execute(..)` method exposed on the `TransactionTemplate`. The following example shows how to do so:

[source,java,indent=0,subs="verbatim,quotes",role="primary"]
.Java
----
	public class SimpleService implements Service {

		// single TransactionTemplate shared amongst all methods in this instance
		private final TransactionTemplate transactionTemplate;

		// use constructor-injection to supply the PlatformTransactionManager
		public SimpleService(PlatformTransactionManager transactionManager) {
			this.transactionTemplate = new TransactionTemplate(transactionManager);
		}

		public Object someServiceMethod() {
			return transactionTemplate.execute(new TransactionCallback() {
				// the code in this method runs in a transactional context
				public Object doInTransaction(TransactionStatus status) {
					updateOperation1();
					return resultOfUpdateOperation2();
				}
			});
		}
	}
----
[source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
.Kotlin
----
	// use constructor-injection to supply the PlatformTransactionManager
	class SimpleService(transactionManager: PlatformTransactionManager) : Service {

		// single TransactionTemplate shared amongst all methods in this instance
		private val transactionTemplate = TransactionTemplate(transactionManager)

		fun someServiceMethod() = transactionTemplate.execute<Any?> {
			updateOperation1()
			resultOfUpdateOperation2()
		}
	}
----


If there is no return value, you can use the convenient `TransactionCallbackWithoutResult` class
with an anonymous class, as follows:

[source,java,indent=0,subs="verbatim,quotes",role="primary"]
.Java
----
	transactionTemplate.execute(new TransactionCallbackWithoutResult() {
		protected void doInTransactionWithoutResult(TransactionStatus status) {
			updateOperation1();
			updateOperation2();
		}
	});
----
[source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
.Kotlin
----
	transactionTemplate.execute(object : TransactionCallbackWithoutResult() {
		override fun doInTransactionWithoutResult(status: TransactionStatus) {
			updateOperation1()
			updateOperation2()
		}
	})
----


Code within the callback can roll the transaction back by calling the
`setRollbackOnly()` method on the supplied `TransactionStatus` object, as follows:

[source,java,indent=0,subs="verbatim,quotes",role="primary"]
.Java
----
	transactionTemplate.execute(new TransactionCallbackWithoutResult() {

		protected void doInTransactionWithoutResult(TransactionStatus status) {
			try {
				updateOperation1();
				updateOperation2();
			} catch (SomeBusinessException ex) {
				status.setRollbackOnly();
			}
		}
	});
----
[source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
.Kotlin
----
	transactionTemplate.execute(object : TransactionCallbackWithoutResult() {

		override fun doInTransactionWithoutResult(status: TransactionStatus) {
			try {
				updateOperation1()
				updateOperation2()
			} catch (ex: SomeBusinessException) {
				status.setRollbackOnly()
			}
		}
	})
----

[[tx-prog-template-settings]]
=== Specifying Transaction Settings

You can specify transaction settings (such as the propagation mode, the isolation level,
the timeout, and so forth) on the `TransactionTemplate` either programmatically or in
configuration. By default, `TransactionTemplate` instances have the
xref:data-access/transaction/declarative/txadvice-settings.adoc[default transactional settings]. The
following example shows the programmatic customization of the transactional settings for
a specific `TransactionTemplate:`

[source,java,indent=0,subs="verbatim,quotes",role="primary"]
.Java
----
	public class SimpleService implements Service {

		private final TransactionTemplate transactionTemplate;

		public SimpleService(PlatformTransactionManager transactionManager) {
			this.transactionTemplate = new TransactionTemplate(transactionManager);

			// the transaction settings can be set here explicitly if so desired
			this.transactionTemplate.setIsolationLevel(TransactionDefinition.ISOLATION_READ_UNCOMMITTED);
			this.transactionTemplate.setTimeout(30); // 30 seconds
			// and so forth...
		}
	}
----
[source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
.Kotlin
----
	class SimpleService(transactionManager: PlatformTransactionManager) : Service {

		private val transactionTemplate = TransactionTemplate(transactionManager).apply {
			// the transaction settings can be set here explicitly if so desired
			isolationLevel = TransactionDefinition.ISOLATION_READ_UNCOMMITTED
			timeout = 30 // 30 seconds
			// and so forth...
		}
	}
----

The following example defines a `TransactionTemplate` with some custom transactional
settings by using Spring XML configuration:

[source,xml,indent=0,subs="verbatim,quotes"]
----
	<bean id="sharedTransactionTemplate"
			class="org.springframework.transaction.support.TransactionTemplate">
		<property name="isolationLevelName" value="ISOLATION_READ_UNCOMMITTED"/>
		<property name="timeout" value="30"/>
	</bean>
----

You can then inject the `sharedTransactionTemplate`
into as many services as are required.

Finally, instances of the `TransactionTemplate` class are thread-safe, in that instances
do not maintain any conversational state. `TransactionTemplate` instances do, however,
maintain configuration state. So, while a number of classes may share a single instance
of a `TransactionTemplate`, if a class needs to use a `TransactionTemplate` with
different settings (for example, a different isolation level), you need to create
two distinct `TransactionTemplate` instances.

[[tx-prog-operator]]
== Using the `TransactionalOperator`

The `TransactionalOperator` follows an operator design that is similar to other reactive
operators. It uses a callback approach (to free application code from having to do the
boilerplate acquisition and release transactional resources) and results in code that is
intention driven, in that your code focuses solely on what you want to do.

NOTE: As the examples that follow show, using the `TransactionalOperator` absolutely
couples you to Spring's transaction infrastructure and APIs. Whether or not programmatic
transaction management is suitable for your development needs is a decision that you have
to make yourself.

Application code that must run in a transactional context and that explicitly uses
the `TransactionalOperator` resembles the next example:

[source,java,indent=0,subs="verbatim,quotes",role="primary"]
.Java
----
	public class SimpleService implements Service {

		// single TransactionalOperator shared amongst all methods in this instance
		private final TransactionalOperator transactionalOperator;

		// use constructor-injection to supply the ReactiveTransactionManager
		public SimpleService(ReactiveTransactionManager transactionManager) {
			this.transactionalOperator = TransactionalOperator.create(transactionManager);
		}

		public Mono<Object> someServiceMethod() {

			// the code in this method runs in a transactional context

			Mono<Object> update = updateOperation1();

			return update.then(resultOfUpdateOperation2).as(transactionalOperator::transactional);
		}
	}
----
[source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
.Kotlin
----
	// use constructor-injection to supply the ReactiveTransactionManager
	class SimpleService(transactionManager: ReactiveTransactionManager) : Service {

		// single TransactionalOperator shared amongst all methods in this instance
		private val transactionalOperator = TransactionalOperator.create(transactionManager)

		suspend fun someServiceMethod() = transactionalOperator.executeAndAwait<Any?> {
			updateOperation1()
			resultOfUpdateOperation2()
		}
	}
----

`TransactionalOperator` can be used in two ways:

* Operator-style using Project Reactor types (`mono.as(transactionalOperator::transactional)`)
* Callback-style for every other case (`transactionalOperator.execute(TransactionCallback<T>)`)

Code within the callback can roll the transaction back by calling the `setRollbackOnly()`
method on the supplied `ReactiveTransaction` object, as follows:

[source,java,indent=0,subs="verbatim,quotes",role="primary"]
.Java
----
	transactionalOperator.execute(new TransactionCallback<>() {

		public Mono<Object> doInTransaction(ReactiveTransaction status) {
			return updateOperation1().then(updateOperation2)
						.doOnError(SomeBusinessException.class, e -> status.setRollbackOnly());
			}
		}
	});
----
[source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
.Kotlin
----
	transactionalOperator.execute(object : TransactionCallback() {

		override fun doInTransactionWithoutResult(status: ReactiveTransaction) {
			updateOperation1().then(updateOperation2)
						.doOnError(SomeBusinessException.class, e -> status.setRollbackOnly())
		}
	})
----

[[tx-prog-operator-cancel]]
=== Cancel Signals

In Reactive Streams, a `Subscriber` can cancel its `Subscription` and stop its
`Publisher`. Operators in Project Reactor, as well as in other libraries, such as `next()`,
`take(long)`, `timeout(Duration)`, and others can issue cancellations. There is no way to
know the reason for the cancellation, whether it is due to an error or a simply lack of
interest to consume further. Since version 5.3 cancel signals lead to a roll back.
As a result it is important to consider the operators used downstream from a transaction
`Publisher`. In particular in the case of a `Flux` or other multi-value `Publisher`,
the full output must be consumed to allow the transaction to complete.


[[tx-prog-operator-settings]]
=== Specifying Transaction Settings

You can specify transaction settings (such as the propagation mode, the isolation level,
the timeout, and so forth) for the `TransactionalOperator`. By default,
`TransactionalOperator` instances have
xref:data-access/transaction/declarative/txadvice-settings.adoc[default transactional settings]. The
following example shows customization of the transactional settings for a specific
`TransactionalOperator:`

[source,java,indent=0,subs="verbatim,quotes",role="primary"]
.Java
----
	public class SimpleService implements Service {

		private final TransactionalOperator transactionalOperator;

		public SimpleService(ReactiveTransactionManager transactionManager) {
			DefaultTransactionDefinition definition = new DefaultTransactionDefinition();

			// the transaction settings can be set here explicitly if so desired
			definition.setIsolationLevel(TransactionDefinition.ISOLATION_READ_UNCOMMITTED);
			definition.setTimeout(30); // 30 seconds
			// and so forth...

			this.transactionalOperator = TransactionalOperator.create(transactionManager, definition);
		}
	}
----
[source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
.Kotlin
----
	class SimpleService(transactionManager: ReactiveTransactionManager) : Service {

		private val definition = DefaultTransactionDefinition().apply {
			// the transaction settings can be set here explicitly if so desired
			isolationLevel = TransactionDefinition.ISOLATION_READ_UNCOMMITTED
			timeout = 30 // 30 seconds
			// and so forth...
		}
		private val transactionalOperator = TransactionalOperator(transactionManager, definition)
	}
----

[[transaction-programmatic-tm]]
== Using the `TransactionManager`

The following sections explain programmatic usage of imperative and reactive transaction
managers.

[[transaction-programmatic-ptm]]
=== Using the `PlatformTransactionManager`

For imperative transactions, you can use a
`org.springframework.transaction.PlatformTransactionManager` directly to manage your
transaction. To do so, pass the implementation of the `PlatformTransactionManager` you
use to your bean through a bean reference. Then, by using the `TransactionDefinition` and
`TransactionStatus` objects, you can initiate transactions, roll back, and commit. The
following example shows how to do so:

[source,java,indent=0,subs="verbatim,quotes",role="primary"]
.Java
----
	DefaultTransactionDefinition def = new DefaultTransactionDefinition();
	// explicitly setting the transaction name is something that can be done only programmatically
	def.setName("SomeTxName");
	def.setPropagationBehavior(TransactionDefinition.PROPAGATION_REQUIRED);

	TransactionStatus status = txManager.getTransaction(def);
	try {
		// put your business logic here
	} catch (MyException ex) {
		txManager.rollback(status);
		throw ex;
	}
	txManager.commit(status);
----
[source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
.Kotlin
----
	val def = DefaultTransactionDefinition()
	// explicitly setting the transaction name is something that can be done only programmatically
	def.setName("SomeTxName")
	def.propagationBehavior = TransactionDefinition.PROPAGATION_REQUIRED

	val status = txManager.getTransaction(def)
	try {
		// put your business logic here
	} catch (ex: MyException) {
		txManager.rollback(status)
		throw ex
	}

	txManager.commit(status)
----


[[transaction-programmatic-rtm]]
=== Using the `ReactiveTransactionManager`

When working with reactive transactions, you can use a
`org.springframework.transaction.ReactiveTransactionManager` directly to manage your
transaction. To do so, pass the implementation of the `ReactiveTransactionManager` you
use to your bean through a bean reference. Then, by using the `TransactionDefinition` and
`ReactiveTransaction` objects, you can initiate transactions, roll back, and commit. The
following example shows how to do so:

[source,java,indent=0,subs="verbatim,quotes",role="primary"]
.Java
----
	DefaultTransactionDefinition def = new DefaultTransactionDefinition();
	// explicitly setting the transaction name is something that can be done only programmatically
	def.setName("SomeTxName");
	def.setPropagationBehavior(TransactionDefinition.PROPAGATION_REQUIRED);

	Mono<ReactiveTransaction> reactiveTx = txManager.getReactiveTransaction(def);

	reactiveTx.flatMap(status -> {

		Mono<Object> tx = ...; // put your business logic here

		return tx.then(txManager.commit(status))
				.onErrorResume(ex -> txManager.rollback(status).then(Mono.error(ex)));
	});
----
[source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
.Kotlin
----
	val def = DefaultTransactionDefinition()
	// explicitly setting the transaction name is something that can be done only programmatically
	def.setName("SomeTxName")
	def.propagationBehavior = TransactionDefinition.PROPAGATION_REQUIRED

	val reactiveTx = txManager.getReactiveTransaction(def)
	reactiveTx.flatMap { status ->

		val tx = ... // put your business logic here

		tx.then(txManager.commit(status))
				.onErrorResume { ex -> txManager.rollback(status).then(Mono.error(ex)) }
	}
----


