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beginner Phase · Spring Boot Fundamentals

application.properties

Configure Spring Boot using application.properties files.

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application.properties

Common Properties

# Server
server.port=8080
server.servlet.context-path=/api

# Database
spring.datasource.url=jdbc:postgresql://localhost:5432/mydb
spring.datasource.username=user
spring.datasource.password=pass
spring.jpa.hibernate.ddl-auto=update

# Logging
logging.level.root=INFO
logging.level.com.example=DEBUG
logging.file.name=app.log

# Jackson (JSON)
spring.jackson.serialization.write-dates-as-timestamps=false
spring.jackson.default-property-inclusion=non_null

Externalized Configuration

# Override via command line
java -jar app.jar --server.port=9090

# Override via environment variable
SERVER_PORT=9090 java -jar app.jar

# Override via profile
java -jar app.jar --spring.profiles.active=prod

Property Precedence (highest to lowest)

  1. Command line arguments
  2. System properties
  3. Environment variables
  4. Profile-specific properties
  5. application.properties
  6. Default properties

Best Practices

Key Principles

  1. Follow SOLID principles
  2. Write clean, readable code
  3. Test thoroughly
  4. Document decisions
  5. Monitor in production

Implementation

  • Start simple, refactor as needed
  • Use established patterns
  • Consider trade-offs
  • Review with peers

Continuous Improvement

  • Learn from incidents
  • Update documentation
  • Share knowledge
  • Mentor others

Key Points

  • Understanding application.properties is essential for production systems
  • Always consider scalability and maintainability
  • Test thoroughly before deploying to production
  • Monitor performance and set up alerting

Common Patterns

  1. Validation: Always validate input at the boundary
  2. Error Handling: Use structured error responses
  3. Logging: Log key events for debugging
  4. Testing: Unit, integration, and load tests
  5. Documentation: Keep docs updated with code changes

Practice Problems

0 / 3 solved
Implement application.properties

Design and implement a solution for application.properties in a backend system. Consider scalability, error handling, and production readiness.

Solution 
// application.properties implementation
// Key aspects: validation, error handling, logging, testing

public class applicationproperties {
    // Production-ready implementation
}
application.properties Edge Cases

Identify and handle edge cases for application.properties. What happens under high load, with invalid input, or during failures?

Solution 
// Edge case handling:
// 1. Null/empty input -> validation
// 2. High load -> rate limiting, queuing
// 3. Failures -> retries, circuit breaker
// 4. Concurrent access -> locks, idempotency
application.properties Testing Strategy

Write a testing strategy for application.properties. Include unit tests, integration tests, and performance tests.

Solution 
// Test plan:
// - Unit: 80% coverage target
// - Integration: API contracts
// - Performance: latency, throughput
// - Chaos: failure injection

Quiz

1. How do you override a property via environment variable?

Question 1 options

2. What is the highest precedence for property override?

Question 2 options

3. What is a common mistake when implementing application.properties?

Question 3 options

Flashcards

Question

Highest property precedence?

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Answer

Command line arguments (--server.port=9090)

Question

Environment variable format?

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Answer

UPPER_CASE: server.port → SERVER_PORT

Question

application.properties best practices

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Answer

Follow SOLID principles, write clean code, test thoroughly, document decisions, and monitor in production.

Revision Notes

Key Takeaways

  • 1. application.properties configures Spring Boot
  • 2. Externalize: command line, env vars, profiles
  • 3. Property precedence: CLI > System > Env > Profile > properties
  • 4. Use profiles for environment-specific config

Interview Tips

  • • Know how to override properties
  • • Understand property precedence

Cheat Sheet

application.properties

  • Server: server.port, server.servlet.context-path
  • DB: spring.datasource., spring.jpa.
  • Override: CLI args > env vars > profiles > properties
  • Env vars: server.port → SERVER_PORT