springboot开发过程中的小坑（持续更新）

1. 启动的Application必须放到一个package下面，如下：

 package com.example.kikidemo;

 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;

 @SpringBootApplication
 public class KikidemoApplication {

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

@SpringBootApplication具有@EnableAutoConfiguration @ComponentScan 等作用

如果Application直接在java目录下，启动时就会提示

** WARNING ** : Your ApplicationContext is unlikely to start due to a @ComponentScan of the default package.

随后出现spring-boo-autoconfigure-xxx.jar找不到的奇怪提示，看起来很像是包冲突，具体如下：

 ** WARNING ** : Your ApplicationContext is unlikely to start due to a @ComponentScan of the default package.

 2018-09-05 11:33:59.783  WARN 108 --- [           main] ationConfigEmbeddedWebApplicationContext : Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.BeanDefinitionStoreException: Failed to read candidate component class: URL [jar:file:/E:/Repository/org/springframework/boot/spring-boot-autoconfigure/1.5.10.RELEASE/spring-boot-autoconfigure-1.5.10.RELEASE.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)
 2018-09-05 11:33:59.786  INFO 108 --- [           main] utoConfigurationReportLoggingInitializer : 

 Error starting ApplicationContext. To display the auto-configuration report re-run your application with 'debug' enabled.
 2018-09-05 11:33:59.792 ERROR 108 --- [           main] o.s.boot.SpringApplication               : Application startup failed

 org.springframework.beans.factory.BeanDefinitionStoreException: Failed to read candidate component class: URL [jar:file:/E:/Repository/org/springframework/boot/spring-boot-autoconfigure/1.5.10.RELEASE/spring-boot-autoconfigure-1.5.10.RELEASE.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.findCandidateComponents(ClassPathScanningCandidateComponentProvider.java:311) ~[spring-context-4.3.14.RELEASE.jar:4.3.14.RELEASE]
     at org.springframework.context.annotation.ClassPathBeanDefinitionScanner.doScan(ClassPathBeanDefinitionScanner.java:272) ~[spring-context-4.3.14.RELEASE.jar:4.3.14.RELEASE]
     at org.springframework.context.annotation.ComponentScanAnnotationParser.parse(ComponentScanAnnotationParser.java:135) ~[spring-context-4.3.14.RELEASE.jar:4.3.14.RELEASE]
     at org.springframework.context.annotation.ConfigurationClassParser.doProcessConfigurationClass(ConfigurationClassParser.java:287) ~[spring-context-4.3.14.RELEASE.jar:4.3.14.RELEASE]
     at org.springframework.context.annotation.ConfigurationClassParser.processConfigurationClass(ConfigurationClassParser.java:245) ~[spring-context-4.3.14.RELEASE.jar:4.3.14.RELEASE]
     at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:198) ~[spring-context-4.3.14.RELEASE.jar:4.3.14.RELEASE]
     at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:167) ~[spring-context-4.3.14.RELEASE.jar:4.3.14.RELEASE]
     at org.springframework.context.annotation.ConfigurationClassPostProcessor.processConfigBeanDefinitions(ConfigurationClassPostProcessor.java:308) ~[spring-context-4.3.14.RELEASE.jar:4.3.14.RELEASE]
     at org.springframework.context.annotation.ConfigurationClassPostProcessor.postProcessBeanDefinitionRegistry(ConfigurationClassPostProcessor.java:228) ~[spring-context-4.3.14.RELEASE.jar:4.3.14.RELEASE]
     at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanDefinitionRegistryPostProcessors(PostProcessorRegistrationDelegate.java:272) ~[spring-context-4.3.14.RELEASE.jar:4.3.14.RELEASE]
     at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:92) ~[spring-context-4.3.14.RELEASE.jar:4.3.14.RELEASE]
     at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:687) ~[spring-context-4.3.14.RELEASE.jar:4.3.14.RELEASE]
     at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:525) ~[spring-context-4.3.14.RELEASE.jar:4.3.14.RELEASE]
     at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:122) ~[spring-boot-1.5.10.RELEASE.jar:1.5.10.RELEASE]
     at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:693) [spring-boot-1.5.10.RELEASE.jar:1.5.10.RELEASE]
     at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:360) [spring-boot-1.5.10.RELEASE.jar:1.5.10.RELEASE]
     at org.springframework.boot.SpringApplication.run(SpringApplication.java:303) [spring-boot-1.5.10.RELEASE.jar:1.5.10.RELEASE]
     at org.springframework.boot.SpringApplication.run(SpringApplication.java:1118) [spring-boot-1.5.10.RELEASE.jar:1.5.10.RELEASE]
     at org.springframework.boot.SpringApplication.run(SpringApplication.java:1107) [spring-boot-1.5.10.RELEASE.jar:1.5.10.RELEASE]
     at KikidemoApplication.main(KikidemoApplication.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:55) ~[spring-boot-autoconfigure-1.5.10.RELEASE.jar:1.5.10.RELEASE]
     at org.springframework.context.annotation.ConditionEvaluator.shouldSkip(ConditionEvaluator.java:102) ~[spring-context-4.3.14.RELEASE.jar:4.3.14.RELEASE]
     at org.springframework.context.annotation.ConditionEvaluator.shouldSkip(ConditionEvaluator.java:81) ~[spring-context-4.3.14.RELEASE.jar:4.3.14.RELEASE]
     at org.springframework.context.annotation.ConditionEvaluator.shouldSkip(ConditionEvaluator.java:64) ~[spring-context-4.3.14.RELEASE.jar:4.3.14.RELEASE]
     at org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider.isConditionMatch(ClassPathScanningCandidateComponentProvider.java:371) ~[spring-context-4.3.14.RELEASE.jar:4.3.14.RELEASE]
     at org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider.isCandidateComponent(ClassPathScanningCandidateComponentProvider.java:355) ~[spring-context-4.3.14.RELEASE.jar:4.3.14.RELEASE]
     at org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider.findCandidateComponents(ClassPathScanningCandidateComponentProvider.java:288) ~[spring-context-4.3.14.RELEASE.jar:4.3.14.RELEASE]
     ... 19 common frames omitted
 Caused by: java.lang.NoClassDefFoundError: org/springframework/jdbc/datasource/embedded/EmbeddedDatabaseType
     at org.springframework.boot.autoconfigure.jdbc.EmbeddedDatabaseConnection.<clinit>(EmbeddedDatabaseConnection.java:49) ~[spring-boot-autoconfigure-1.5.10.RELEASE.jar:1.5.10.RELEASE]
     at org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration$EmbeddedDatabaseCondition.getMatchOutcome(DataSourceAutoConfiguration.java:211) ~[spring-boot-autoconfigure-1.5.10.RELEASE.jar:1.5.10.RELEASE]
     at org.springframework.boot.autoconfigure.condition.SpringBootCondition.matches(SpringBootCondition.java:47) ~[spring-boot-autoconfigure-1.5.10.RELEASE.jar:1.5.10.RELEASE]
     ... 25 common frames omitted
 Caused by: java.lang.ClassNotFoundException: org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseType
     at java.net.URLClassLoader.findClass(URLClassLoader.java:381) ~[na:1.8.0_162]
     at java.lang.ClassLoader.loadClass(ClassLoader.java:424) ~[na:1.8.0_162]
     at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:338) ~[na:1.8.0_162]
     at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ~[na:1.8.0_162]
     ... 28 common frames omitted

 Process finished with exit code 1