Conditional bean creation in Spring Boot - Step-by-Step Execution

Concept Flow - Conditional bean creation

Start Application

↓

Check Condition on Bean

↓

Create Bean

↓

Continue Application Startup

Spring Boot checks a condition before creating a bean. If the condition is true, the bean is created; otherwise, it is skipped.

Execution Sample

Spring Boot

@Bean
@ConditionalOnProperty(name = "feature.enabled", havingValue = "true")
public MyService myService() {
    return new MyService();
}

This code creates the MyService bean only if the property 'feature.enabled' is set to 'true'.

Execution Table

Step	Action	Condition Checked	Condition Result	Bean Created
1	Start application context	N/A	N/A	No
2	Evaluate @ConditionalOnProperty for 'feature.enabled'	Is 'feature.enabled' == 'true'?	True	Yes, create MyService bean
3	Register MyService bean in context	N/A	N/A	Yes
4	Continue application startup	N/A	N/A	Beans ready
5	Application ready to use	N/A	N/A	Yes

💡 Bean creation depends on condition; if false, bean is skipped and not registered.

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
feature.enabled	undefined	true	true	true
MyService bean	not created	evaluated	created	created

Key Moments - 2 Insights

Why is the MyService bean not created if the property 'feature.enabled' is false or missing?

Because @ConditionalOnProperty checks the property value at Step 2 in the execution_table. If the condition is false, the bean creation is skipped as shown in the flow.

Can multiple beans use different conditions to control their creation?

Yes, each bean can have its own @Conditional annotation with different conditions, so Spring evaluates each separately during startup.

Visual Quiz - 3 Questions

Look at the execution table, at which step is the condition for bean creation evaluated?

A Step 2

B Step 3

C Step 1

D Step 4

💡 Hint

Check the 'Condition Checked' column in the execution_table.

If the property 'feature.enabled' is set to false, what happens to the MyService bean?

A It is created anyway

B It is not created

C It is created but disabled

D Application fails to start

💡 Hint

Refer to the 'Condition Result' and 'Bean Created' columns in the execution_table.

If you add another bean with a different condition, how does Spring handle bean creation?

A It only creates the first bean with a true condition

B It creates all beans regardless of conditions

C It evaluates each bean's condition separately

D It throws an error if multiple conditions exist

💡 Hint

See key_moments about multiple beans and conditions.

Concept Snapshot

Conditional bean creation in Spring Boot:
- Use @Conditional annotations (e.g., @ConditionalOnProperty)
- Spring checks condition during startup
- Bean is created only if condition is true
- Skips bean creation if condition is false
- Allows flexible, environment-based bean setup

Full Transcript

Conditional bean creation in Spring Boot means the framework decides whether to create a bean based on a condition. For example, using @ConditionalOnProperty, Spring checks if a property is set to a specific value. If true, it creates the bean; if false, it skips it. This happens during application startup. This approach helps to enable or disable features easily without changing code. Each bean can have its own condition, and Spring evaluates them one by one. This makes your application flexible and configurable.

Practice

1. What is the main purpose of using @ConditionalOnProperty in Spring Boot?

easy

A. To disable all beans in the application

B. To always create a bean regardless of configuration

C. To create a bean only if a specific property is set in the configuration

D. To create beans only during testing

Solution

1. Step 1: Understand the role of @ConditionalOnProperty

   This annotation checks if a property is set in the application configuration.

2. Step 2: Effect on bean creation

   If the property matches the condition, Spring Boot creates the bean; otherwise, it skips it.

3. Final Answer:

   To create a bean only if a specific property is set in the configuration -> Option C

4. Quick Check:

   Conditional bean creation = property check [OK]

Hint: Remember: @ConditionalOnProperty controls bean creation by config [OK]

Common Mistakes:

• Thinking it always creates beans
• Confusing it with disabling all beans
• Assuming it only works in tests

2. Which of the following is the correct way to use @ConditionalOnProperty to create a bean only when feature.enabled is true?

easy

A. @ConditionalOnProperty(property = "feature.enabled", value = "true")

B. @ConditionalOnProperty(name = "feature.enabled", havingValue = "true")

C. @ConditionalOnProperty(key = "feature.enabled", equals = "true")

D. @ConditionalOnProperty(enabled = "feature.enabled", isTrue = true)

Solution

1. Step 1: Recall correct annotation parameters

   The correct parameters are name for the property key and havingValue for the expected value.

2. Step 2: Match with options

   @ConditionalOnProperty(name = "feature.enabled", havingValue = "true") uses name and havingValue correctly, others use invalid parameter names.

3. Final Answer:

   @ConditionalOnProperty(name = "feature.enabled", havingValue = "true") -> Option B

4. Quick Check:

   Correct params = name + havingValue [OK]

Hint: Use 'name' and 'havingValue' parameters for @ConditionalOnProperty [OK]

Common Mistakes:

• Using wrong parameter names like 'property' or 'key'
• Confusing 'havingValue' with 'value'
• Using boolean true without quotes

3. Given this Spring Boot bean definition:

@Bean
@ConditionalOnProperty(name = "app.feature", havingValue = "enabled")
public Service myService() {
    return new Service();
}

What happens if the property app.feature=disabled is set in application.properties?

medium

A. The bean myService is created and available

B. The bean is created but disabled

C. Application fails to start with error

D. The bean myService is NOT created

Solution

1. Step 1: Understand the condition

   The bean is created only if app.feature equals "enabled".

2. Step 2: Check the property value

   The property is set to "disabled", which does not match "enabled".

3. Final Answer:

   The bean myService is NOT created -> Option D

4. Quick Check:

   Property mismatch = no bean creation [OK]

Hint: Bean creates only if property matches havingValue exactly [OK]

Common Mistakes:

• Assuming bean creates regardless of property value
• Thinking app fails to start on mismatch
• Believing bean is created but inactive

4. Consider this bean definition:

@Bean
@ConditionalOnProperty(name = "service.enabled", havingValue = "true")
public Service service() {
    return new Service();
}

Why does the bean never get created even when service.enabled=true is set in application.properties?

medium

A. The property key name is incorrect or misspelled

B. The property is a string but havingValue expects a boolean

C. The bean method is missing @Component annotation

D. The bean method must be static to work with @ConditionalOnProperty

Solution

1. Step 1: Verify property key spelling

   If the property key in application.properties is misspelled or different, condition fails.

2. Step 2: Check other options

   HavingValue compares strings, so boolean type mismatch is not an issue; @Component is not needed on @Bean methods; static is not required.

3. Final Answer:

   The property key name is incorrect or misspelled -> Option A

4. Quick Check:

   Property key must match exactly [OK]

Hint: Check property key spelling carefully for conditional beans [OK]

Common Mistakes:

• Assuming boolean type mismatch causes failure
• Thinking @Component is needed on @Bean methods
• Believing bean methods must be static

5. You want to create two beans of the same type but only one should be active based on a property mode which can be "simple" or "advanced".
Which is the best way to define these beans using @ConditionalOnProperty?

hard

A. Use @ConditionalOnProperty(name = "mode", havingValue = "simple") on the simple bean and @ConditionalOnProperty(name = "mode", havingValue = "advanced") on the advanced bean

B. Use @ConditionalOnProperty(name = "mode") on both beans without havingValue

C. Create both beans without conditions and select one at runtime

D. Use @ConditionalOnProperty(name = "mode", matchIfMissing = true) on both beans

Solution

1. Step 1: Understand the requirement

   Only one bean should be active depending on the property value "simple" or "advanced".

2. Step 2: Apply conditional annotations

   Using @ConditionalOnProperty with havingValue set to "simple" or "advanced" on each bean ensures only one bean loads.

3. Step 3: Evaluate other options

   Use @ConditionalOnProperty(name = "mode") on both beans without havingValue lacks value check, so both beans may load; Create both beans without conditions and select one at runtime loads both always; Use @ConditionalOnProperty(name = "mode", matchIfMissing = true) on both beans activates both if property missing.

4. Final Answer:

   Use @ConditionalOnProperty(name = "mode", havingValue = "simple") on the simple bean and @ConditionalOnProperty(name = "mode", havingValue = "advanced") on the advanced bean -> Option A

5. Quick Check:

   Use havingValue to select one bean by property [OK]

Hint: Use havingValue to pick one bean per property value [OK]

Common Mistakes:

• Not specifying havingValue causing both beans to load
• Trying to select bean at runtime instead of conditionally
• Using matchIfMissing on both beans causing conflicts