Spring Boot - Advanced Patterns
How can you create a bean only if no other bean of the same type exists and a specific property
service.enabled is set to true?How can you create a bean only if no other bean of the same type exists and a specific property service.enabled is set to true?
hard📝 Application Q9 of 15
Step-by-Step Solution
Solution:
Step 1: Use @ConditionalOnMissingBean to check bean absence
This ensures the bean is created only if no other bean of the same type exists.Step 2: Use @ConditionalOnProperty with havingValue = "true"
This ensures the bean is created only if the property is set to true.Step 3: Verify option correctness
@Bean @ConditionalOnMissingBean @ConditionalOnProperty(name = "service.enabled", havingValue = "true") public Service service() { return new Service(); } correctly combines both conditions. @Bean @ConditionalOnBean(Service.class) @ConditionalOnProperty(name = "service.enabled", havingValue = "true") public Service service() { return new Service(); } requires bean presence, @Bean @ConditionalOnMissingBean @ConditionalOnProperty(name = "service.enabled", havingValue = "false") public Service service() { return new Service(); } checks for false property, @Bean @ConditionalOnClass(Service.class) @ConditionalOnProperty(name = "service.enabled") public Service service() { return new Service(); } checks class presence only.Final Answer:
Option A correctly creates bean if missing and property true -> Option AQuick Check:
Combine missing bean and property true for conditional creation [OK]
Quick Trick: Use missing bean and property true to create unique conditional bean [OK]
Common Mistakes:
- Using @ConditionalOnBean instead of missing bean
- Checking for false property instead of true
- Confusing class presence with bean presence
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