Conditional bean creation in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a bean only if a property is set to true.

Spring Boot

@Bean
@ConditionalOnProperty(name = "feature.enabled", havingValue = "[1]")
public Feature feature() {
    return new Feature();
}

Drag options to blanks, or click blank then click option'

Afalse

Benabled

Cyes

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'false' instead of 'true' disables the bean creation.

Using arbitrary strings like 'yes' or 'enabled' won't match the property value.

The @ConditionalOnProperty annotation checks if the property feature.enabled has the value true to create the bean.

2fill in blank

medium

Complete the code to create a bean only if another bean named 'dataSource' exists.

Spring Boot

@Bean
@ConditionalOnBean(name = "[1]")
public Repository repository() {
    return new Repository();
}

Drag options to blanks, or click blank then click option'

Aservice

BdataSource

CcacheManager

DentityManager

Attempts:

3 left

💡 Hint

Common Mistakes

Using a bean name that does not exist causes the bean not to be created.

Confusing bean names like 'entityManager' or 'cacheManager' when the condition is on 'dataSource'.

The @ConditionalOnBean annotation creates the bean only if a bean named dataSource exists in the context.

3fill in blank

hard

Fix the error in the code to create a bean only if a class 'com.example.Service' is present.

Spring Boot

@Bean
@ConditionalOnClass(name = "[1]")
public Service service() {
    return new Service();
}

Drag options to blanks, or click blank then click option'

Acom.example.Service

Bcom.example.services.Service

Cexample.Service

Dcom.example.service

Attempts:

3 left

💡 Hint

Common Mistakes

Using package name only without class name.

Incorrect capitalization or missing parts of the package.

The @ConditionalOnClass annotation requires the full class name including package and class name exactly as com.example.Service.

4fill in blank

hard

Fill both blanks to create a bean only if property 'app.mode' equals 'prod' and a bean named 'cacheManager' exists.

Spring Boot

@Bean
@ConditionalOnProperty(name = "app.mode", havingValue = "[1]")
@ConditionalOnBean(name = "[2]")
public CacheService cacheService() {
    return new CacheService();
}

Drag options to blanks, or click blank then click option'

Aprod

Bdev

CcacheManager

DdataSource

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'dev' instead of 'prod' disables the bean creation.

Checking for a bean named 'dataSource' instead of 'cacheManager'.

The bean cacheService is created only if the property app.mode is 'prod' and the bean named cacheManager exists.

5fill in blank

hard

Fill all three blanks to create a bean only if class 'com.example.Feature' is present, property 'feature.enabled' is 'true', and bean 'featureRepository' exists.

Spring Boot

@Bean
@ConditionalOnClass(name = "[1]")
@ConditionalOnProperty(name = "feature.enabled", havingValue = "[2]")
@ConditionalOnBean(name = "[3]")
public Feature feature() {
    return new Feature();
}

Drag options to blanks, or click blank then click option'

Acom.example.Feature

Btrue

CfeatureRepository

Dcom.example.Features

Attempts:

3 left

💡 Hint

Common Mistakes

Misspelling the class name or package.

Using 'false' instead of 'true' for the property.

Checking for a bean with a wrong name.

The bean feature is created only if the class com.example.Feature is present, the property feature.enabled is 'true', and the bean named featureRepository exists.

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