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📘 Spring Boot Transaction Management – @Transactional (Part-2)

 

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1️⃣ Hierarchy of Transaction Managers (Page-1 Diagram)

Core Interfaces & Classes

1. TransactionManager
   • Top-level marker interface.
2. PlatformTransactionManager (extends TransactionManager)
   • Defines 3 core methods:
     • getTransaction()
     • commit()
     • rollback()
3. AbstractPlatformTransactionManager (abstract class)
   • Provides default implementation for:
     • Transaction lifecycle
     • Commit & rollback handling
   • Concrete managers extend this.

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Concrete Implementations

Transaction Manager	Used With	Type
DataSourceTransactionManager	JDBC	Local
JdbcTransactionManager	JDBC	Local
HibernateTransactionManager	Hibernate	Local
JpaTransactionManager	JPA	Local
JtaTransactionManager	JTA	Distributed

✅ Important Note:

• JDBC, JPA, Hibernate → Local Transactions
• JTA → Distributed Transactions (multiple DBs / MQs)

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2️⃣ Transaction Management Types

🔹 Declarative Transaction Management

• Done using @Transactional
• Managed by Spring automatically
• Clean & recommended

🔹 Programmatic Transaction Management

• Manual control using code
• More flexible but complex

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3️⃣ Declarative Transaction Management (@Transactional)

Basic Example (from PDF)

@Component
public class User {

    @Transactional
    public void updateUser() {
        System.out.println("Update query to update user DB values");
    }
}

How Spring Chooses Transaction Manager

• Based on DataSource / JPA / Hibernate
• Spring Boot auto-configures the correct one

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4️⃣ Explicit Transaction Manager Configuration (Page-2)

@Bean
public DataSource dataSource() {
    DriverManagerDataSource ds = new DriverManagerDataSource();
    ds.setDriverClassName("org.h2.Driver");
    ds.setUrl("jdbc:h2:mem:testdb");
    ds.setUsername("sa");
    ds.setPassword("");
    return ds;
}

@Bean
public PlatformTransactionManager userTransactionManager(
        DataSource dataSource) {
    return new DataSourceTransactionManager(dataSource);
}

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5️⃣ Using Named Transaction Manager

@Component
public class UserDeclarative {

    @Transactional(transactionManager = "userTransactionManager")
    public void updateUserProgrammatic() {
        System.out.println("Insert Query ran");
        System.out.println("Update Query ran");
    }
}

📌 Use case:
When multiple DataSources exist in the application.

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6️⃣ Programmatic Transaction Management

Two Approaches

✅ Approach-1: PlatformTransactionManager

Steps:

1. Create TransactionDefinition
2. Start transaction
3. Commit / Rollback manually

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✅ Approach-2: TransactionTemplate (Recommended)

• Cleaner than approach-1
• Handles commit & rollback internally

transactionTemplate.execute(status -> {
    // DB operations
    return null;
});

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7️⃣ Transaction Propagation (Page-3 & 4)

Propagation defines how a method behaves when a transaction already exists.

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🔹 REQUIRED (Default)

@Transactional(propagation = Propagation.REQUIRED)

• If parent txn exists → use it
• Else → create new txn

✅ Most commonly used

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🔹 REQUIRES_NEW

@Transactional(propagation = Propagation.REQUIRES_NEW)

• Suspends parent transaction
• Creates a new transaction
• Parent resumes after completion

📌 Used for audit logs, notifications

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🔹 SUPPORTS

@Transactional(propagation = Propagation.SUPPORTS)

• If txn exists → use it
• Else → run without transaction

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🔹 NOT_SUPPORTED

@Transactional(propagation = Propagation.NOT_SUPPORTED)

• Suspends parent transaction
• Always runs without transaction

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🔹 MANDATORY

@Transactional(propagation = Propagation.MANDATORY)

• If txn exists → use it
• Else → ❌ Exception

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🔹 NEVER

@Transactional(propagation = Propagation.NEVER)

• If txn exists → ❌ Exception
• Else → run normally

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8️⃣ Transaction Synchronization Check (Page-5 Output)

TransactionSynchronizationManager.isActualTransactionActive();
TransactionSynchronizationManager.getCurrentTransactionName();

Used to verify:

• Is transaction active?
• Current transaction name

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🔥 EXTRA NOTES (Very Important – Not in PDF)

✅ Rollback Rules

• By default, Spring rolls back on:
  • RuntimeException
  • Error
• ❌ Does NOT rollback on Checked Exception

👉 Fix:

@Transactional(rollbackFor = Exception.class)

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✅ Self-Invocation Problem

this.innerMethod(); // @Transactional ignored

✔ Solution:

• Call from another bean
• Or use ApplicationContext.getBean()

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✅ Proxy Limitation

• @Transactional works only on public methods
• Uses AOP proxy

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🎯 Interview Questions & Answers

Q1. What is PlatformTransactionManager?

Ans:
It is the central interface in Spring that manages transactions using getTransaction(), commit(), and rollback().

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Q2. Difference between REQUIRED and REQUIRES_NEW?

Ans:

• REQUIRED → joins existing transaction
• REQUIRES_NEW → suspends existing and creates new one

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Q3. Which transaction manager is used for JPA?

Ans:
JpaTransactionManager

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Q4. Why JTA is used?

Ans:
For distributed transactions involving multiple databases or message queues.

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Q5. Does @Transactional work on private methods?

Ans:
❌ No. Only public methods due to proxy mechanism.

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Q6. What happens if a checked exception occurs?

Ans:
Transaction will not rollback unless explicitly configured.

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Q7. Which is better: Declarative or Programmatic?

Ans:
Declarative (@Transactional) – cleaner & recommended
Programmatic – used only when fine-grained control is needed

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