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1. Overview

The auto-configuration mechanism in Spring Boot attempts to automatically configure an application based on its dependencies.

In this quick tutorial, we’ll see how Spring Boot can log its auto-configuration report at startup time.

2. Sample Application

Let’s write a simple Spring Boot application that we’ll use in our examples:

@SpringBootApplication
public class App {
    public static void main(String[] args) {
        SpringApplication.run(App.class, args);
    }
}

3. Application Properties Approach

In starting up this application, we don’t get a lot of information about how or why Spring Boot decided to compose our application’s configuration.

But, we can have Spring Boot create a report simply by enabling debug mode in our application.properties file:

debug=true

Or our application.yml file:

debug: true

4. Command-Line Approach

Or, if we don’t want to use the properties file approach, we can trigger the auto-configuration report by starting the application with the –debug switch:

$ java -jar myproject-0.0.1-SNAPSHOT.jar --debug

5. Report Output

The auto-configuration report contains information about the classes that Spring Boot found on the classpath and configured automatically. It also shows information about classes that are known to Spring Boot but were not found on the classpath.

And, because we’ve set debug=true, then we see it in our output:

============================
CONDITIONS EVALUATION REPORT
============================


Positive matches:
-----------------

   AopAutoConfiguration matched:
      - @ConditionalOnClass found required classes 'org.springframework.context.annotation.EnableAspectJAutoProxy', 
        'org.aspectj.lang.annotation.Aspect', 'org.aspectj.lang.reflect.Advice', 'org.aspectj.weaver.AnnotatedElement'; 
        @ConditionalOnMissingClass did not find unwanted class (OnClassCondition)
      - @ConditionalOnProperty (spring.aop.auto=true) matched (OnPropertyCondition)

   AopAutoConfiguration.CglibAutoProxyConfiguration matched:
      - @ConditionalOnProperty (spring.aop.proxy-target-class=true) matched (OnPropertyCondition)

   AuditAutoConfiguration#auditListener matched:
      - @ConditionalOnMissingBean (types: org.springframework.boot.actuate.audit.listener.AbstractAuditListener; 
        SearchStrategy: all) did not find any beans (OnBeanCondition)

   AuditAutoConfiguration.AuditEventRepositoryConfiguration matched:
      - @ConditionalOnMissingBean (types: org.springframework.boot.actuate.audit.AuditEventRepository; 
        SearchStrategy: all) did not find any beans (OnBeanCondition)

   AuditEventsEndpointAutoConfiguration#auditEventsEndpoint matched:
      - @ConditionalOnBean (types: org.springframework.boot.actuate.audit.AuditEventRepository; 
        SearchStrategy: all) found bean 'auditEventRepository'; 
        @ConditionalOnMissingBean (types: org.springframework.boot.actuate.audit.AuditEventsEndpoint; 
        SearchStrategy: all) did not find any beans (OnBeanCondition)
      - @ConditionalOnEnabledEndpoint no property management.endpoint.auditevents.enabled found 
        so using endpoint default (OnEnabledEndpointCondition)


Negative matches:
-----------------

   ActiveMQAutoConfiguration:
      Did not match:
         - @ConditionalOnClass did not find required classes 'javax.jms.ConnectionFactory', 
           'org.apache.activemq.ActiveMQConnectionFactory' (OnClassCondition)

   AopAutoConfiguration.JdkDynamicAutoProxyConfiguration:
      Did not match:
         - @ConditionalOnProperty (spring.aop.proxy-target-class=false) did not find property 
           'proxy-target-class' (OnPropertyCondition)

   ArtemisAutoConfiguration:
      Did not match:
         - @ConditionalOnClass did not find required classes 'javax.jms.ConnectionFactory', 
           'org.apache.activemq.artemis.jms.client.ActiveMQConnectionFactory' (OnClassCondition)

   AtlasMetricsExportAutoConfiguration:
      Did not match:
         - @ConditionalOnClass did not find required class 'io.micrometer.atlas.AtlasMeterRegistry' 
           (OnClassCondition)

   AtomikosJtaConfiguration:
      Did not match:
         - @ConditionalOnClass did not find required class 'com.atomikos.icatch.jta.UserTransactionManager' 
           (OnClassCondition)

6. Conclusion

In this quick tutorial, we saw how to display and read a Spring Boot auto-configuration report.

And as always, the source code for the above example can be found over on GitHub.

I just announced the new Spring Boot 2 material, coming in REST With Spring:

>> CHECK OUT THE LESSONS

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