I've opened something strange thing.
Why does Spring Boot not require a data source when you create Application class in package like this:
main
------ java
-------------teach
-------------------- SpringBootApplication.class
And why doest It require a data source when you create Application class without any package like this:
main
------ java
-------------------- SpringBootApplication.class
In both ways I have the same class:
@SpringBootApplication
public class SpringBootWithoutDbExamplApplication {
public static void main(String[] args) {
SpringApplication.run(SpringBootWithoutDbExamplApplication.class, args);
}
}
and the same pom:
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<optional>true</optional>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<configuration>
<excludes>
<exclude>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
</exclude>
</excludes>
</configuration>
</plugin>
</plugins>
</build>
But when I run project without package I get error:
2021-04-14 22:53:54.274 ERROR 5872 --- [ main] o.s.boot.SpringApplication : Application run failed
org.springframework.beans.factory.BeanDefinitionStoreException: Failed to read candidate component class: URL [jar:file:C:\Users\altuk\.m2\repository\org\springframework\boot\spring-boot-autoconfigure\2.4.4\spring-boot-autoconfigure-2.4.4.jar!/org/springframework/boot/autoconfigure/jdbc/DataSourceAutoConfiguration$EmbeddedDatabaseConfiguration.class]; nested exception is java.lang.IllegalStateException: Could not evaluate condition on org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration$EmbeddedDatabaseConfiguration due to org/springframework/jdbc/datasource/embedded/EmbeddedDatabaseType not found. Make sure your own configuration does not rely on that class. This can also happen if you are @ComponentScanning a springframework package (e.g. if you put a @ComponentScan in the default package by mistake)
at org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider.scanCandidateComponents(ClassPathScanningCandidateComponentProvider.java:452) ~[spring-context-5.3.5.jar:5.3.5]
at org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider.findCandidateComponents(ClassPathScanningCandidateComponentProvider.java:315) ~[spring-context-5.3.5.jar:5.3.5]
at org.springframework.context.annotation.ClassPathBeanDefinitionScanner.doScan(ClassPathBeanDefinitionScanner.java:276) ~[spring-context-5.3.5.jar:5.3.5]
at org.springframework.context.annotation.ComponentScanAnnotationParser.parse(ComponentScanAnnotationParser.java:132) ~[spring-context-5.3.5.jar:5.3.5]
at org.springframework.context.annotation.ConfigurationClassParser.doProcessConfigurationClass(ConfigurationClassParser.java:296) ~[spring-context-5.3.5.jar:5.3.5]
at org.springframework.context.annotation.ConfigurationClassParser.processConfigurationClass(ConfigurationClassParser.java:250) ~[spring-context-5.3.5.jar:5.3.5]
at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:207) ~[spring-context-5.3.5.jar:5.3.5]
at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:175) ~[spring-context-5.3.5.jar:5.3.5]
at org.springframework.context.annotation.ConfigurationClassPostProcessor.processConfigBeanDefinitions(ConfigurationClassPostProcessor.java:331) ~[spring-context-5.3.5.jar:5.3.5]
at org.springframework.context.annotation.ConfigurationClassPostProcessor.postProcessBeanDefinitionRegistry(ConfigurationClassPostProcessor.java:247) ~[spring-context-5.3.5.jar:5.3.5]
at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanDefinitionRegistryPostProcessors(PostProcessorRegistrationDelegate.java:311) ~[spring-context-5.3.5.jar:5.3.5]
at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:112) ~[spring-context-5.3.5.jar:5.3.5]
at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:746) ~[spring-context-5.3.5.jar:5.3.5]
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:564) ~[spring-context-5.3.5.jar:5.3.5]
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:144) ~[spring-boot-2.4.4.jar:2.4.4]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:769) ~[spring-boot-2.4.4.jar:2.4.4]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:761) ~[spring-boot-2.4.4.jar:2.4.4]
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:426) ~[spring-boot-2.4.4.jar:2.4.4]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:326) ~[spring-boot-2.4.4.jar:2.4.4]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1313) ~[spring-boot-2.4.4.jar:2.4.4]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1302) ~[spring-boot-2.4.4.jar:2.4.4]
at SpringBootWithoutDbExamplApplication.main(SpringBootWithoutDbExamplApplication.java:8) ~[classes/:na]
Caused by: java.lang.IllegalStateException: Could not evaluate condition on org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration$EmbeddedDatabaseConfiguration due to org/springframework/jdbc/datasource/embedded/EmbeddedDatabaseType not found. Make sure your own configuration does not rely on that class. This can also happen if you are @ComponentScanning a springframework package (e.g. if you put a @ComponentScan in the default package by mistake)
at org.springframework.boot.autoconfigure.condition.SpringBootCondition.matches(SpringBootCondition.java:54) ~[spring-boot-autoconfigure-2.4.4.jar:2.4.4]
at org.springframework.context.annotation.ConditionEvaluator.shouldSkip(ConditionEvaluator.java:108) ~[spring-context-5.3.5.jar:5.3.5]
at org.springframework.context.annotation.ConditionEvaluator.shouldSkip(ConditionEvaluator.java:88) ~[spring-context-5.3.5.jar:5.3.5]
at org.springframework.context.annotation.ConditionEvaluator.shouldSkip(ConditionEvaluator.java:71) ~[spring-context-5.3.5.jar:5.3.5]
at org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider.isConditionMatch(ClassPathScanningCandidateComponentProvider.java:513) ~[spring-context-5.3.5.jar:5.3.5]
at org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider.isCandidateComponent(ClassPathScanningCandidateComponentProvider.java:496) ~[spring-context-5.3.5.jar:5.3.5]
at org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider.scanCandidateComponents(ClassPathScanningCandidateComponentProvider.java:430) ~[spring-context-5.3.5.jar:5.3.5]
... 21 common frames omitted
Caused by: java.lang.NoClassDefFoundError: org/springframework/jdbc/datasource/embedded/EmbeddedDatabaseType
at org.springframework.boot.jdbc.EmbeddedDatabaseConnection.<clinit>(EmbeddedDatabaseConnection.java:55) ~[spring-boot-2.4.4.jar:2.4.4]
at org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration$EmbeddedDatabaseCondition.getMatchOutcome(DataSourceAutoConfiguration.java:136) ~[spring-boot-autoconfigure-2.4.4.jar:2.4.4]
at org.springframework.boot.autoconfigure.condition.SpringBootCondition.matches(SpringBootCondition.java:47) ~[spring-boot-autoconfigure-2.4.4.jar:2.4.4]
... 27 common frames omitted
Caused by: java.lang.ClassNotFoundException: org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseType
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:602) ~[na:na]
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178) ~[na:na]
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:522) ~[na:na]
... 30 common frames omitted
One thing to notice about spring boot conventions that might lead to the answer.
When it starts, it has to build an application context, so it needs to "understand" where to search for the beans.
By convention, spring boot searches for the beans in the package where the class annotated with @SpringBootApplication resides and all the packages beneath.
Example:
If you place the class annotated with @SpringBootApplication in com.myorg.myapp
It will look for the beans in:
com.myorg.myapp
com.myorg.myapp.abc
com.myorg.myapp.abc.def.any.inner.place
It won't search for the beans in:
com.myorg.anotherapp
com.myorg
org
I'm sure you've got the point.
Now when you place the main class annotated with @SpringBootApplication in the default package its like saying to spring - scan everything
I believe this causes the issue because spring starts searching in the places it shouldn't.
In addition to that this has a sever performance implications, because if your application has third-party dependencies which do not even have beans - spring will search there as well.
So bottom line, you should always place the main class in the package that is unique to your application.