Conditional bean creation in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output when using @ConditionalOnProperty with missing property?

Consider a Spring Boot application with a bean annotated as @ConditionalOnProperty(name = "feature.enabled", havingValue = "true"). If the property feature.enabled is not set in application.properties, what happens to the bean?

Spring Boot

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

A The bean is created regardless of the property value.

B The bean is created with default value because the property is missing.

C The bean is not created because the property is missing and does not match the required value.

D The application fails to start due to missing property.

💡 Hint

Think about how @ConditionalOnProperty behaves when the property is absent.

The @ConditionalOnProperty annotation creates the bean only if the specified property exists and matches the given value. If the property is missing, the condition fails and the bean is not created.

📝 Syntax

intermediate

Identify the correct syntax for conditional bean creation using @ConditionalOnClass

Which of the following bean definitions correctly uses @ConditionalOnClass to create a bean only if DataSource.class is present on the classpath?

A

@Bean
@ConditionalOnClass(className = "javax.sql.DataSource")
public MyBean myBean() { return new MyBean(); }

B

@Bean
@ConditionalOnClass(name = "javax.sql.DataSource")
public MyBean myBean() { return new MyBean(); }

C

@Bean
@ConditionalOnClass(classes = DataSource.class)
public MyBean myBean() { return new MyBean(); }

D

@Bean
@ConditionalOnClass(DataSource.class)
public MyBean myBean() { return new MyBean(); }

💡 Hint

Check the official attribute name for @ConditionalOnClass.

The correct attribute for @ConditionalOnClass is a varargs of Class types, so using @ConditionalOnClass(DataSource.class) is correct. The other options use incorrect attribute names or syntax.

🔧 Debug

advanced

Why does this conditional bean not get created despite correct property?

Given the following code snippet, the bean specialService is not created even though app.special.enabled=true is set in application.properties. What is the most likely cause?

Spring Boot

@Configuration
public class SpecialConfig {
    @Bean
    @ConditionalOnProperty(name = "app.special.enabled", havingValue = "true", matchIfMissing = false)
    public SpecialService specialService() {
        return new SpecialService();
    }
}

A The property name in the annotation does not exactly match the property key in the properties file.

B The matchIfMissing attribute should be true to create the bean.

C The bean method is missing the @Component annotation.

D The SpecialService class is not annotated with @Service.

💡 Hint

Check for exact spelling and case sensitivity in property names.

The @ConditionalOnProperty annotation requires the property name to exactly match the key in the properties file. If there is a typo or case mismatch, the condition fails and the bean is not created.

❓ state_output

advanced

What is the state of the application context with multiple conditional beans?

In a Spring Boot app, two beans are defined with these conditions: Bean A: @ConditionalOnProperty(name = "feature.a.enabled", havingValue = "true") Bean B: @ConditionalOnProperty(name = "feature.b.enabled", havingValue = "true") If feature.a.enabled=true and feature.b.enabled=false in application.properties, which beans exist in the application context?

A Only Bean B is created; Bean A is not created.

B Only Bean A is created; Bean B is not created.

C Neither Bean A nor Bean B is created.

D Both Bean A and Bean B are created.

💡 Hint

Consider how each property value affects its bean creation independently.

Each bean's creation depends on its own property. Since feature.a.enabled is true, Bean A is created. Since feature.b.enabled is false, Bean B is not created.

🧠 Conceptual

expert

Which condition causes a bean to be created only if another bean is missing?

You want to create a bean only if a bean of type DataSource is NOT already defined in the Spring context. Which annotation achieves this?

A @ConditionalOnMissingBean(DataSource.class)

B @ConditionalOnBean(DataSource.class)

C @ConditionalOnProperty(name = "datasource.enabled", havingValue = "false")

D @ConditionalOnClass(name = "javax.sql.DataSource")

💡 Hint

Think about the annotation that checks absence of a bean.

The @ConditionalOnMissingBean annotation creates the bean only if no bean of the specified type exists in the context. The other annotations check for presence or properties, not absence.