Overview

Learning Approach

This By Example series teaches Spring Framework through code-first learning with heavily annotated examples. Each example is self-contained and runnable, demonstrating specific Spring Framework concepts.

Target: 75-90 examples achieving 95% Spring Framework coverage

Annotation Density: 1.0-2.25 comment lines per code line (per example)

Format: All examples in both Java and Kotlin

Why By Example?

Traditional tutorials often provide long explanations before showing code. This approach inverts that pattern:

Code First: Start with working, runnable examples Inline Documentation: Every line annotated with // => explaining what happens Incremental Complexity: Simple examples first, building to advanced patterns Islamic Finance Context: Real-world scenarios (Zakat, Murabaha, Sadaqah)

Structure

Beginner Examples (0-50% Coverage)

Topics Covered:

• IoC Container basics
• Bean definitions with @Configuration and @Bean
• Component scanning with @Component, @Service, @Repository
• Dependency injection (constructor, setter, field)
• Bean scopes (singleton, prototype)
• Lifecycle callbacks (@PostConstruct, @PreDestroy)
• Property injection with @Value
• Profile-based configuration (@Profile)

Example Count: ~25-30 examples

Skill Level: No prior Spring knowledge required

Intermediate Examples (50-85% Coverage)

Topics Covered:

• Advanced dependency injection (qualifiers, primary beans)
• Data access with JdbcTemplate
• Transaction management (@Transactional)
• Spring AOP (aspects, pointcuts, advice types)
• Event publishing and handling
• SpEL (Spring Expression Language)
• Resource handling
• Validation with Bean Validation API
• Testing with Spring Test framework

Example Count: ~30-35 examples

Skill Level: Completed beginner examples or equivalent knowledge

Advanced Examples (85-95% Coverage)

Topics Covered:

• Custom bean post-processors
• Advanced AOP (custom annotations, around advice)
• Programmatic transaction management
• Custom scope implementations
• Conditional bean registration
• Spring Web MVC (controllers, REST APIs)
• Exception handling strategies
• Async processing with @Async
• Caching with @Cacheable
• Integration testing strategies

Example Count: ~20-25 examples

Skill Level: Completed intermediate examples or production Spring experience

Example Format

Each example follows a five-part structure:

1. Concept Introduction

Brief explanation of what the example demonstrates.

Example:

Concept: Constructor injection - Spring injects dependencies via constructor parameters, ensuring immutability and required dependencies.

2. Islamic Finance Scenario

Real-world context using Islamic finance concepts.

Example:

Scenario: ZakatService requires a ZakatRepository to persist Zakat payments. Constructor injection ensures the repository is always available.

3. Code Example (Heavily Annotated)

Self-contained, runnable code with inline annotations.

Java Example:

@Service  // => Marks as Spring-managed service component
public class ZakatService {

    private final ZakatRepository repository;  // => Final field - immutable

    // => Constructor injection (recommended)
    // => Spring automatically injects repository parameter
    public ZakatService(ZakatRepository repository) {
        this.repository = repository;          // => Dependency injected
    }                                          // => Repository cannot be null

    @Transactional  // => Transaction boundary
    public void recordPayment(BigDecimal amount) {
        repository.save(new ZakatRecord(amount));  // => Persists within transaction
    }                                              // => Auto-commit on success
}

Kotlin Example:

@Service  // => Spring-managed service
class ZakatService(
    private val repository: ZakatRepository  // => Constructor injection
) {  // => Concise Kotlin syntax

    @Transactional  // => Transaction boundary
    fun recordPayment(amount: BigDecimal) {
        repository.save(ZakatRecord(amount))  // => Persists record
    }  // => Auto-commit/rollback
}

4. Key Takeaways

Bullet points highlighting critical concepts.

Example:

• Constructor injection ensures required dependencies are never null
• @Service enables component scanning
• @Transactional provides declarative transaction management
• Final fields promote immutability

5. Common Mistakes

Anti-patterns and how to avoid them.

Example:

❌ Mistake: Using field injection

@Autowired
private ZakatRepository repository;  // => Hard to test, hides dependencies

✅ Correct: Use constructor injection

public ZakatService(ZakatRepository repository) {
    this.repository = repository;  // => Explicit, testable, immutable
}

Islamic Finance Context

Examples use authentic Islamic finance scenarios:

Zakat (Obligatory Charity)

Definition: 2.5% annual payment on qualifying wealth above nisab threshold

Examples:

• Calculating Zakat on savings
• Recording Zakat payments
• Tracking distribution to eligible recipients

Murabaha (Cost-Plus Financing)

Definition: Shariah-compliant financing where financier buys asset and sells at disclosed profit

Examples:

• Calculating payment schedules
• Recording installments
• Profit distribution calculations

Sadaqah (Voluntary Charity)

Definition: Voluntary charitable giving beyond obligatory Zakat

Examples:

• Recording donations
• Tracking campaigns
• Generating tax receipts

Qard Hassan (Benevolent Loan)

Definition: Interest-free loan as act of charity

Examples:

• Loan disbursement
• Repayment tracking
• Beneficiary management

How to Use This Series

Sequential Learning (Recommended)

Follow examples in order:

1. Start: Beginner examples (foundational concepts)
2. Progress: Intermediate examples (practical patterns)
3. Master: Advanced examples (production techniques)

Reference Learning

Jump to specific topics using index:

• Need transaction management? → Intermediate #15
• Need REST APIs? → Advanced #08
• Need custom annotations? → Advanced #12

Practice-Based Learning

After each example:

1. Read the annotated code
2. Type the code yourself (muscle memory)
3. Modify the example (experiment)
4. Test your changes (verify understanding)

Prerequisites

Required Knowledge

Java or Kotlin:

• OOP concepts (classes, interfaces, inheritance)
• Generics basics
• Lambda expressions (Java 8+) or Kotlin functions

Build Tools:

• Maven or Gradle basics
• Dependency management concepts

Database Basics:

• SQL fundamentals (SELECT, INSERT, UPDATE)
• JDBC concepts (connections, statements)

Setup Requirements

Complete Initial Setup to have:

• Java 17+ or Kotlin 1.9+ installed
• Maven or Gradle configured
• IDE configured (IntelliJ IDEA recommended)

Learning Outcomes

After completing all examples, you will:

Understand:

• Spring IoC container architecture
• Dependency injection patterns and best practices
• Bean lifecycle and scopes
• Transaction management strategies
• AOP concepts and applications

Apply:

• Java-based configuration effectively
• Component scanning and stereotype annotations
• JdbcTemplate for data access
• Declarative transaction management
• Testing strategies with Spring Test

Evaluate:

• When to use Spring Framework vs Spring Boot
• Trade-offs between injection types
• Appropriate transaction boundaries
• Performance implications of AOP

Example Catalog

Core Container (Examples 1-15)

Beginner Level:

1. Basic bean definition with @Bean
2. Constructor injection
3. Setter injection
4. Component scanning with @Component
5. Autowiring by type
6. Singleton vs prototype scope
7. @PostConstruct and @PreDestroy
8. @Value property injection
9. Profile-based configuration
10. Multiple configuration classes

Intermediate Level:

1. @Qualifier for disambiguation
2. @Primary for default beans
3. Method injection with @Lookup
4. Circular dependency resolution
5. Lazy initialization with @Lazy

Data Access (Examples 16-35)

Beginner Level:

1. JdbcTemplate basics - insert
2. JdbcTemplate - query with RowMapper
3. JdbcTemplate - update and delete
4. Named parameters with NamedParameterJdbcTemplate

Intermediate Level:

1. @Transactional basics
2. Transaction propagation (REQUIRED, REQUIRES_NEW)
3. Transaction isolation levels
4. Rollback rules
5. Programmatic transaction management
6. Multiple DataSource configuration
7. Connection pooling with HikariCP
8. Database initialization with schema.sql

Advanced Level:

1. Custom TransactionManager
2. Distributed transactions overview
3. Optimistic locking patterns
4. Batch operations with JdbcTemplate
5. Stored procedure calls
6. Custom exception translation
7. JDBC testing strategies
8. Transaction testing with @Transactional rollback

AOP (Examples 36-50)

Intermediate Level:

1. Basic aspect with @Before advice
2. @After and @AfterReturning advice
3. @Around advice for method interception
4. Pointcut expressions
5. Custom annotations as pointcuts
6. Passing arguments to advice
7. Aspect ordering

Advanced Level:

1. Introduction aspects (@DeclareParents)
2. Performance monitoring aspect
3. Logging aspect
4. Security aspect (authorization checks)
5. Retry logic with AOP
6. Caching with AOP
7. Async execution with AOP
8. AOP testing strategies

Web MVC (Examples 51-70)

Intermediate Level:

1. Basic @Controller with request mapping
2. @RequestParam for query parameters
3. @PathVariable for URL variables
4. @RequestBody for JSON input
5. @ResponseBody for JSON output
6. Model and View resolution
7. Form handling with @ModelAttribute
8. Validation with Bean Validation API
9. Exception handling with @ExceptionHandler
10. RESTful API with @RestController

Advanced Level:

1. Content negotiation
2. Custom argument resolvers
3. Interceptors for request processing
4. File upload handling
5. Async request processing
6. Server-Sent Events (SSE)
7. CORS configuration
8. Security headers
9. REST API testing
10. Integration testing with MockMvc

Advanced Topics (Examples 71-90)

1. Event publishing with ApplicationEventPublisher
2. Event listening with @EventListener
3. SpEL in annotations
4. Resource loading
5. Custom property sources
6. Custom scope implementation
7. Bean post-processors
8. @Conditional annotations
9. Caching with @Cacheable
10. Async methods with @Async
11. Scheduling with @Scheduled
12. Custom validators
13. Type conversion with ConversionService
14. Internationalization (i18n)
15. Profile-specific beans
16. Environment abstraction
17. Application context events
18. Graceful shutdown
19. Health checks
20. Metrics collection

Navigation

Start Learning:

• Beginner Examples - Examples 1-30 (0-50% coverage)
• Intermediate Examples - Examples 31-65 (50-85% coverage)
• Advanced Examples - Examples 66-90 (85-95% coverage)

Other Learning Paths:

• Overview - Conceptual introduction
• Initial Setup - Installation and project setup
• Quick Start - Complete working application