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Spring Boot conditional annotations

Spring Boot conditional annotations are metadata markers used to control whether a specific configuration, bean, or component is registered and loaded into the application context based on specific runtime conditions.^[600-developer__spring__springboot.md]

Mechanism

These annotations are primarily found within *AutoConfiguration classes.^[600-developer__spring__springboot.md] They allow the framework to automatically enable or disable functionality depending on the presence of other beans, the classpath, or specific property values, thus reducing the need for manual configuration.^[600-developer__spring__springboot.md]

Debugging and Analysis

To understand why a specific auto-configuration (and its associated conditional logic) was applied or rejected, developers can analyze the application.^[600-developer__spring__springboot.md]

  • Startup Reports: Adding --debug to the command line or the system property -Ddebug prints a report of all auto-configuration decisions to the console.^[600-developer__spring__springboot.md]
  • Actuator Endpoint: In an application with the Actuator enabled, the /actuator/conditions endpoint (or its JMX equivalent) provides detailed information about conditional matches and mismatches.^[600-developer__spring__springboot.md]

Common Annotations

While the source material generally refers to them as @Conditional* annotations^[600-developer__spring__springboot.md], a specific example of a conditional check mentioned is @ConditionalOnExpression.^[600-developer__spring__springboot.md] This annotation allows features to be toggled on or off based on SpEL (Spring Expression Language) expressions that often evaluate properties from the Environment.^[600-developer__spring__springboot.md]

Sources

^[600-developer__spring__springboot.md]