Does Spring @Transactional attribute work on a private method?

Proxy mechanism: The Backbone of @Transactional

Spring's @Transactional, much like a sophisticated concert, operates through proxies orchestrating the show from the backstage. But here’s the catch — these proxies can only manage your public performances (methods), not your private rehearsals.

Why so? It's because of a Java language constraint that private methods can't be overridden, making them invisible to proxies. Think of it as trying to manage an invisible actor on the stage. That'd be a disaster!

Exception Handling in Private methods: Surprises in Disguise

While @Transactional might give the cold shoulder to private methods, it’s not ignorant of errors occurring in them. Even though it can't see private methods, any exceptions that these methods throw are still detected by the transaction boundary set up by the public method.

Self-Invocation: A Wolf in Sheep's Clothing

Do not be tricked by self-invocation! In the Spring context, a self-invoked method doesn’t pass through the proxy, hence it sidesteps any transactional trellis defined by @Transactional.

@Service
public class TransactionalService {

    // Here should be a drumroll 🥁
    @Transactional
    public void performService() {
        // Nope, not a magical portal, just method invocation
        internalMethod();
    }
    
    // ....and the crowd goes silent
    private void internalMethod() {
        // ... secret code ...
    }
}
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Alternative Superhero: AspectJ

If Batman (@Transactional) fails to protect your private transactions, you can call Superman — a.k.a AspectJ. AspectJ has no issues with method visibility since it operates at the bytecode level. It's like Superman who can go where Batman can't, defying the rules of visibility.

Including AspectJ: Superman's Signal Device

Just like getting Superman's attention requires a special signal, ensuring AspectJ's support in your project requires additional configuration involving the AdviceMode.ASPECTJ and aspectjrt dependency.

Maven AspectJ Plugin: Superman's Costume

Don't forget to equip Superman with his costume. Configure the AspectJ plugin in your Maven build to enable bytecode weaving:

<plugin>
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>aspectj-maven-plugin</artifactId>
    <version>{version}</version>
    <configuration>
        <complianceLevel>{java-version}</complianceLevel>
    </configuration>
    <executions>
        <execution>
            <goals>
                <goal>compile</goal>
                <goal>test-compile</goal>
            </goals>
        </execution>
    </executions>
</plugin>
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Honing AspectJ: Supercharging Superman

Flexibility and performance are key. Tune AspectJ parameters for optimal performance, especially with Java 8 or later. It's like customizing Superman's powers to battle different types of villains!

Plan B: @Transactional Alternatives

When all else fails, we can always rely on TransactionTemplate. It might not be the superhero you wished for, but it’s the one you need. The TransactionTemplate allows manual management of transactions and gives you more control in scenarios where annotations might not suffice.

Hands-On Transaction Management

public void executeWithTransactionTemplate() {
    new TransactionTemplate(transactionManager).execute(status -> {
        // Not today, @Transactional
        doSomethingPrivate();
        return null;
    });
}
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