为什么Spring Boot需要数据源？
Why does SpringBoot require data source?
我打开了一些奇怪的东西。
为什么在这样的包中创建应用程序 class 时 Spring 引导不需要数据源：
主要
------ java
-------------教
-------------------- SpringBootApplication.class
以及为什么在创建应用程序时需要数据源 class 而没有像这样的任何包：
主要
------ java
-------------------- SpringBootApplication.class
两种方式我都一样class:
@SpringBootApplication
public class SpringBootWithoutDbExamplApplication {
public static void main(String[] args) {
SpringApplication.run(SpringBootWithoutDbExamplApplication.class, args);
}
}
和相同的 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>
但是当我 运行 项目没有包时我得到错误：
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.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
可能是因为 spring 引导自动配置。
尝试通过属性禁用它。
spring:
autoconfigure:
exclude:
- org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration
关于 spring 引导约定的注意事项可能会导致答案。
启动时，它必须构建一个应用程序上下文，因此它需要“了解”到哪里搜索 bean。
按照惯例，spring 引导搜索包中的 beans，其中 class 注释为 @SpringBootApplication 所在的包及其下方的所有包。
示例：
如果你把注解为@SpringBootApplication的class放在com.myorg.myapp
它将在以下位置寻找豆子：
com.myorg.myapp
com.myorg.myapp.abc
com.myorg.myapp.abc.def.any.inner.place
它不会在以下位置搜索 bean：
com.myorg.anotherapp
com.myorg
org
我相信你明白了。
现在，当您将带有 @SpringBootApplication 注释的主要 class 放在默认包中时，就像对 spring - 扫描所有内容
我认为这是导致问题的原因，因为 spring 开始在不应该搜索的地方搜索。
除此之外，这还会对服务器性能产生影响，因为如果您的应用程序具有甚至没有 bean 的第三方依赖项 - spring 也会在那里进行搜索。
所以最重要的是，您应该始终将主要 class 放在您的应用程序独有的包中。
我打开了一些奇怪的东西。
为什么在这样的包中创建应用程序 class 时 Spring 引导不需要数据源：
主要
------ java
-------------教
-------------------- SpringBootApplication.class
以及为什么在创建应用程序时需要数据源 class 而没有像这样的任何包：
主要
------ java
-------------------- SpringBootApplication.class
两种方式我都一样class:
@SpringBootApplication
public class SpringBootWithoutDbExamplApplication {
public static void main(String[] args) {
SpringApplication.run(SpringBootWithoutDbExamplApplication.class, args);
}
}
和相同的 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>
但是当我 运行 项目没有包时我得到错误：
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.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
可能是因为 spring 引导自动配置。 尝试通过属性禁用它。
spring:
autoconfigure:
exclude:
- org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration
关于 spring 引导约定的注意事项可能会导致答案。
启动时，它必须构建一个应用程序上下文，因此它需要“了解”到哪里搜索 bean。
按照惯例，spring 引导搜索包中的 beans，其中 class 注释为 @SpringBootApplication 所在的包及其下方的所有包。
示例：
如果你把注解为@SpringBootApplication的class放在com.myorg.myapp
它将在以下位置寻找豆子：
com.myorg.myapp
com.myorg.myapp.abc
com.myorg.myapp.abc.def.any.inner.place
它不会在以下位置搜索 bean：
com.myorg.anotherapp
com.myorg
org
我相信你明白了。
现在，当您将带有 @SpringBootApplication 注释的主要 class 放在默认包中时，就像对 spring - 扫描所有内容
我认为这是导致问题的原因，因为 spring 开始在不应该搜索的地方搜索。
除此之外，这还会对服务器性能产生影响，因为如果您的应用程序具有甚至没有 bean 的第三方依赖项 - spring 也会在那里进行搜索。
所以最重要的是，您应该始终将主要 class 放在您的应用程序独有的包中。