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🌱 Spring Boot – @Profile

1️⃣ What is @Profile in Spring Boot?

@Profile is a Spring annotation used to activate or deactivate beans based on the current runtime environment.

👉 In simple words:
Different environments → Different configurations → Different beans

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2️⃣ Why Do We Need @Profile? (Problem Statement)

In real-world applications, we usually have multiple environments:

Environment	Purpose
Dev / Local	Development
QA / Stage	Testing
Prod	Live users

Each environment has different configurations, such as:

• Database credentials
• URLs and ports
• Timeout values
• Retry limits
• Throttle values

📌 As shown on Page 1 of the PDF,
Dev, QA, and Prod machines all connect to different databases with different credentials.

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3️⃣ Without @Profile – The Problem

❌ If we put all configurations in application.properties:

• Values will clash
• Risk of using prod DB in dev
• Manual changes required before deployment
• High chance of misconfiguration

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4️⃣ Profiling Concept (Core Idea)

Spring Boot supports profile-based configuration files:

application.properties              (default)
application-dev.properties
application-qa.properties
application-prod.properties

📌 Only one or more profiles are activated at runtime.

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5️⃣ How Spring Chooses Configuration Files

Priority Order:

1. application.properties
2. application-{activeProfile}.properties

Example:

spring.profiles.active=dev

✔ Spring loads:

• application.properties
• application-dev.properties

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6️⃣ Activating Profiles (From PDF + Extra)

✅ Method 1: application.properties

spring.profiles.active=qa

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✅ Method 2: Command Line

mvn spring-boot:run -Dspring-boot.run.profiles=prod

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✅ Method 3: POM.xml

<profiles>
  <profile>
    <id>production</id>
    <properties>
      <spring-boot.run.profiles>prod</spring-boot.run.profiles>
    </properties>
  </profile>
</profiles>

Run using:

mvn spring-boot:run -Pproduction

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7️⃣ Using @Profile on Beans

Example: Common Codebase, Different Beans

@Component
@Profile("dev")
public class DevDBConnection {
}

@Component
@Profile("prod")
public class ProdDBConnection {
}

✔ Only matching profile bean is created.

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8️⃣ Multiple Profiles at Once (From PDF)

spring.profiles.active=dev,qa

✔ Beans with:

• @Profile("dev")
• @Profile("qa")
  are both loaded.

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9️⃣ Common Codebase – Multiple Applications Use Case

📌 PDF Scenario (Page 3):

• 2 applications
• Same codebase
• Bean should be created only for one application

Solution:

@Component
@Profile("app1")
public class App1SpecificBean {
}

✔ Bean is created only when app1 profile is active.

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🔟 Difference: @Profile vs @ConditionalOnProperty

Feature	@Profile	@ConditionalOnProperty
Based On	Environment	Property value
Use Case	Dev / QA / Prod	Feature toggle
Flexibility	Medium	High
Complexity	Low	Medium

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1️⃣1️⃣ Advantages of @Profile

✅ Clean environment separation
✅ Avoids accidental prod usage
✅ Easy deployment configuration
✅ Works well with CI/CD
✅ Reduces manual changes

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1️⃣2️⃣ Disadvantages of @Profile

❌ Hardcoded environment names
❌ Too many profiles can confuse
❌ Not ideal for feature toggles
❌ Needs proper documentation

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1️⃣3️⃣ Best Practices (Added)

✔ Use profiles mainly for environment differences
✔ Avoid putting business logic behind profiles
✔ Log active profiles at startup
✔ Combine with @ConditionalOnProperty if needed
✔ Never store secrets in Git

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🧠 Interview Questions & Answers

Q1️⃣ What is @Profile in Spring Boot?

Answer:
@Profile is used to enable or disable beans based on the active environment profile.

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Q2️⃣ Where do we define active profiles?

Answer:

• application.properties
• Command line
• JVM arguments
• POM.xml

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Q3️⃣ Can we activate multiple profiles?

Answer:
Yes, using comma-separated values.

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Q4️⃣ Difference between @Profile and @ConditionalOnProperty?

Answer:
@Profile is environment-based, while @ConditionalOnProperty is configuration-value based.

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Q5️⃣ What happens if no profile is active?

Answer:
Only application.properties is loaded.

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Q6️⃣ Is @Profile evaluated at runtime?

Answer:
No, it is evaluated during application startup.

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Q7️⃣ Can we apply @Profile on @Configuration classes?

Answer:
Yes, both on beans and configuration classes.

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Q8️⃣ Real-world use of @Profile?

Answer:
Different DBs, APIs, credentials, logging levels per environment.

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📌 One-Line Summary

@Profile helps manage environment-specific configurations and beans cleanly and safely in Spring Boot.

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