This document discusses Spring Boot and how it works under the hood. It explains how Spring Boot auto-configures applications and components like data access using Java configuration. Spring Boot uses conditions and conditional annotations to determine whether to auto-configure and activate beans and components. It also describes how to create a custom starter and configure conditions.

1. SPRING BOOT
UNDER THE
HOOD
@NICOLAS_FRANKEL

2. ME, MYSELF AND I
@nicolas_frankel #springboot
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 Developer/Software -
/Solution Architect
• Java
• As consultant

3. HYBRIS, AN SAP COMPANY
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@nicolas_frankel #springboot

4. @nicolas_frankel #springboot
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5. @nicolas_frankel #springboot
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6. SPRING BOOT ACTUATOR
<dependency>
<groupId>
org.springframework.boot
</groupId>
<artifactId>
spring-boot-starter-actuator
</artifactId>
</dependency>
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7. /HEALTH
{
"status" : "UP",
"diskSpace" : {
"status" : "UP",
"total" : 499055067136,
"free" : 254812135424,
"threshold" : 10485760
},
"db" : {
"status" : "UP",
"database" : "HSQL Database Engine",
"hello" : 1
}
}
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8. SPRING BOOT
Works well until:
• It doesn’t anymore
• Or you want to change the
default behavior
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9. CONFIGURATION – POM.XML
<dependency>
<groupId>
org.springframework.boot
</groupId>
<artifactId>
spring-boot-starter-data-jpa
</artifactId>
</dependency>
<dependency>
<groupId>org.hsqldb</groupId>
<artifactId>hsqldb</artifactId>
<scope>runtime</scope>
</dependency>
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10. LET’S CHECK HOW IT WORKS
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11. STARTERS DEPENDENCIES
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12. SPRING-BOOT-AUTOCONFIGURE.JAR
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13. SPRING.FACTORIES
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14. @JPAREPOSITORIESAUTOCONFIGURATION
@Configuration
@ConditionalOnBean(DataSource.class)
@ConditionalOnClass(JpaRepository.class)
@ConditionalOnMissingBean({
JpaRepositoryFactoryBean.class,
JpaRepositoryConfigExtension.class })
@ConditionalOnProperty(
prefix = "spring.data.jpa.repositories",
name = "enabled", havingValue = "true",
matchIfMissing = true)
@Import(JpaRepositoriesAutoConfigureRegistrar.class)
@AutoConfigureAfter(
HibernateJpaAutoConfiguration.class)
public class JpaRepositoriesAutoConfiguration {
}
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15. @CONDITIONAL
@ConditionalOnBean
@ConditionalOnClass
@ConditionalOnMissingBean
@ConditionalOnProperty
etc.
@nicolas_frankel #springboot
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16. REMEMBER @PROFILE?
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface Profile {
String[] value();
}
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17. THIS IS THE NEW @PROFILE
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE,
ElementType.METHOD})
@Documented
@Conditional(ProfileCondition.class)
public @interface Profile {
String[] value();
}
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18. @CONDITIONAL & CONDITION
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19. @CONDITIONAL & CONDITION
Enables calling of a @Bean-
annotated method
• In the context of a
@Configuration class
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20. ENOUGH TALK…
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21. OUT-OF-THE-BOX CONDITIONS
Condition Description
OnBeanCondition Checks if a bean is in the Spring factory
OnClassCondition Checks if a class is on the classpath
OnExpressionCondition Evalutates a SPeL expression
OnJavaCondition Checks the version of Java
OnJndiCondition Checks if a JNDI branch exists
OnPropertyCondition Checks if a property exists
OnResourceCondition Checks if a resource exists
OnWebApplicationCondition Checks if a WebApplicationContext exists
@nicolas_frankel #springboot
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22. COMPOSITE CONDITIONS
Condition Description
AllNestedConditions AND condition
AnyNestedConditions OR condition
NoneNestedCondition NOT condition
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23. OUR OWN STARTER
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24. Q&A
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http://blog.frankel.ch/
@nicolas_frankel
http://frankel.in/
https://git.io/v2f3O