Conditional bean creation in Spring Boot - Mini Project: Build & Apply

Conditional Bean Creation in Spring Boot

📖 Scenario: You are building a Spring Boot application that needs to create a bean only when a specific condition is met. This is useful when you want to enable or disable features based on configuration or environment.

🎯 Goal: Learn how to create a bean conditionally using Spring Boot annotations so that the bean is only created when a certain property is set to true.

📋 What You'll Learn

Create a configuration class

Define a bean method inside the configuration class

Use a conditional annotation to create the bean only if a property is true

Add the property to application.properties to control bean creation

💡 Why This Matters

🌍 Real World

Conditional bean creation is useful in real applications to enable or disable features without changing code, just by changing configuration.

💼 Career

Understanding conditional bean creation helps you build flexible and configurable Spring Boot applications, a common requirement in professional Java development.

1

Create a configuration class

Create a class called FeatureConfig and annotate it with @Configuration.

Spring Boot

@Configuration
// Your code here

Hint

The @Configuration annotation marks the class as a source of bean definitions.

2

Add a property to control the feature

Add a property called feature.enabled with value true to the application.properties file.

Spring Boot

import org.springframework.context.annotation.Configuration;

@Configuration
public class FeatureConfig {

}

# Add the property below in application.properties
# Your code here

Hint

The application.properties file controls configuration properties for your Spring Boot app.

3

Define a conditional bean method

Inside FeatureConfig, create a method called featureBean that returns a new String with value "Feature is enabled". Annotate this method with @Bean and @ConditionalOnProperty(name = "feature.enabled", havingValue = "true").

Spring Boot

import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Bean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;

@Configuration
public class FeatureConfig {
    // Your code here
}

# application.properties
feature.enabled=true

Hint

The @ConditionalOnProperty annotation creates the bean only if the property matches the given value.

4

Complete the setup and verify bean creation

Ensure the FeatureConfig class imports @Bean and @ConditionalOnProperty annotations correctly and the application.properties file contains feature.enabled=true to enable the bean creation.

Spring Boot

import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Bean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;

@Configuration
public class FeatureConfig {
    @Bean
    @ConditionalOnProperty(name = "feature.enabled", havingValue = "true")
    public String featureBean() {
        return "Feature is enabled";
    }
}

# application.properties
# Ensure feature.enabled=true is set
# Your code here

Hint

Double-check your imports and property file to ensure the bean is created only when the property is true.

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