If you want an embedded database (H2, HSQL or Derby), please put it on the classpath.

今天学习SpringBoot，使用SpringBoot整合SpringMVC和SpringDataJpa后，写了一个简单的小demo，使用启动类启动后，出现了如下问题：

***************************
APPLICATION FAILED TO START
***************************

Description:

Failed to auto-configure a DataSource: 'spring.datasource.url' is not specified and no embedded datasource could be auto-configured.

Reason: Failed to determine a suitable driver class


Action:

Consider the following:

	If you want an embedded database (H2, HSQL or Derby), please put it on the classpath.
	If you have database settings to be loaded from a particular profile you may need to activate it (no profiles are currently active).


Process finished with exit code 1

按照网上所说的，找到了如下解决办法(加上红框中这句代码)：

但是这样做了之后，并没有解决问题，而是出现了一个新的问题：

***************************
APPLICATION FAILED TO START
***************************
 
Description:
 
Field userDao in com.abc.service.impl.UserServiceImpl required a bean of type 'com.abc.dao.IUserDao' that could not be found.
 
 
Action:
 
Consider defining a bean of type 'com.abc.dao.IUserDao' in your configuration.

 于是再去网上找答案，找到了如下解决方法(又加上了包体扫描。如果不是用JPA的实现而是用Mybatis，在Mapper接口上加@Mapper注解即可解决上述问题)：

这样的话，上面的问题是解决掉了，但是我的controller根本扫描不到，结果就是浏览器的请求全是404。

无奈之下，只好将这个项目删掉重新写了一遍，以上网上搜索的方法全都没使用，结果却正常。至此问题解决了，但是不知道为何如此灵异！只好先记录下来！ 

程序启动类：

/**
* <p>Title: SpringbootApplicationRunner</p>  
* <p>Description: SpringBoot启动类</p>  
* @author Jiang 
* @date 2019年3月4日
*/
@SpringBootApplication
public class SpringbootApplicationRunner {

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

}

程序启动信息：

13:03:23.036 [main] DEBUG org.springframework.boot.devtools.settings.DevToolsSettings - Included patterns for restart : []
13:03:23.036 [main] DEBUG org.springframework.boot.devtools.settings.DevToolsSettings - Excluded patterns for restart : [/spring-boot-starter/target/classes/, /spring-boot-autoconfigure/target/classes/, /spring-boot-starter-[\w-]+/, /spring-boot/target/classes/, /spring-boot-actuator/target/classes/, /spring-boot-devtools/target/classes/]
13:03:23.036 [main] DEBUG org.springframework.boot.devtools.restart.ChangeableUrls - Matching URLs for reloading : [file:/D:/Java%e7%8f%ad%e8%af%be%e5%a0%82%e8%b5%84%e6%96%99/workspace4/springboot/target/classes/]

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.0.0.RELEASE)

2019-03-04 13:03:23.597  INFO 4284 --- [  restartedMain] com.abc.SpringbootApplicationRunner      : Starting SpringbootApplicationRunner on JN-PC with PID 4284 (started by jiang in D:\Java班课堂资料\workspace4\springboot)
2019-03-04 13:03:23.600  INFO 4284 --- [  restartedMain] com.abc.SpringbootApplicationRunner      : No active profile set, falling back to default profiles: default
2019-03-04 13:03:23.680  INFO 4284 --- [  restartedMain] ConfigServletWebServerApplicationContext : Refreshing [e-mail]5a01d: startup date [Mon Mar 04 13:03:23 CST 2019]; root of context hierarchy
2019-03-04 13:03:25.876  INFO 4284 --- [  restartedMain] trationDelegate$BeanPostProcessorChecker : Bean 'org.springframework.transaction.annotation.ProxyTransactionManagementConfiguration' of type [org.springframework.transaction.annotation.ProxyTransactionManagementConfiguration$$EnhancerBySpringCGLIB$$a71426c] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)
2019-03-04 13:03:26.996  INFO 4284 --- [  restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2019-03-04 13:03:27.039  INFO 4284 --- [  restartedMain] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2019-03-04 13:03:27.039  INFO 4284 --- [  restartedMain] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/8.5.28
2019-03-04 13:03:27.070  INFO 4284 --- [ost-startStop-1] o.a.catalina.core.AprLifecycleListener   : The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: [E:\program files\develop\Java\jdk1.8.0_162\bin;C:\WINDOWS\Sun\Java\bin;C:\WINDOWS\system32;C:\WINDOWS;E:/program files/develop/Java/jdk1.8.0_162/bin/../jre/bin/server;E:/program files/develop/Java/jdk1.8.0_162/bin/../jre/bin;E:/program files/develop/Java/jdk1.8.0_162/bin/../jre/lib/amd64;E:\program files\develop\Java\jdk1.8.0_162\bin;E:\program files\develop\Java\jdk1.8.0_162\bin;E:\program files\develop\apache-maven-3.5.2\bin;C:\Program Files (x86)\Intel\iCLS Client\;C:\Program Files\Intel\iCLS Client\;C:\windows\system32;C:\windows;C:\windows\System32\Wbem;C:\windows\System32\WindowsPowerShell\v1.0\;C:\Program Files (x86)\NVIDIA Corporation\PhysX\Common;C:\Program Files (x86)\Intel\Intel(R) Management Engine Components\DAL;C:\Program Files\Intel\Intel(R) Management Engine Components\DAL;C:\Program Files (x86)\Intel\Intel(R) Management Engine Components\IPT;C:\Program Files\Intel\Intel(R) Management Engine Components\IPT;"E:\program files\develop\Java\jdk1.8.0_162\bin;C:\WINDOWS\system32";C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\WINDOWS\System32\WindowsPowerShell\v1.0\;E:\program files\develop\MySQL\MySQL Server 5.5\bin;E:\program files\develop\TortoiseSVN\bin;E:\program files\develop\Git\cmd;E:\program files\develop\TortoiseGit\bin;C:\WINDOWS\system32;C:\WINDOWS\System32\OpenSSH\;C:\Users\jiang\AppData\Local\Microsoft\WindowsApps;;E:\program files\develop\eclipse;;.]
2019-03-04 13:03:27.276  INFO 4284 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2019-03-04 13:03:27.276  INFO 4284 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 3596 ms
2019-03-04 13:03:27.540  INFO 4284 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean  : Servlet dispatcherServlet mapped to [/]
2019-03-04 13:03:27.546  INFO 4284 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'characterEncodingFilter' to: [/*]
2019-03-04 13:03:27.546  INFO 4284 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
2019-03-04 13:03:27.546  INFO 4284 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'httpPutFormContentFilter' to: [/*]
2019-03-04 13:03:27.546  INFO 4284 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'requestContextFilter' to: [/*]
2019-03-04 13:03:27.950  INFO 4284 --- [  restartedMain] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Starting...
2019-03-04 13:03:28.436  INFO 4284 --- [  restartedMain] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Start completed.
2019-03-04 13:03:28.488  INFO 4284 --- [  restartedMain] j.LocalContainerEntityManagerFactoryBean : Building JPA container EntityManagerFactory for persistence unit 'default'
2019-03-04 13:03:28.521  INFO 4284 --- [  restartedMain] o.hibernate.jpa.internal.util.LogHelper  : HHH000204: Processing PersistenceUnitInfo [
	name: default
	...]
2019-03-04 13:03:28.666  INFO 4284 --- [  restartedMain] org.hibernate.Version                    : HHH000412: Hibernate Core {5.2.14.Final}
2019-03-04 13:03:28.666  INFO 4284 --- [  restartedMain] org.hibernate.cfg.Environment            : HHH000206: hibernate.properties not found
2019-03-04 13:03:28.721  INFO 4284 --- [  restartedMain] o.hibernate.annotations.common.Version   : HCANN000001: Hibernate Commons Annotations {5.0.1.Final}
2019-03-04 13:03:28.866  INFO 4284 --- [  restartedMain] org.hibernate.dialect.Dialect            : HHH000400: Using dialect: org.hibernate.dialect.MySQL5Dialect
2019-03-04 13:03:29.636  INFO 4284 --- [  restartedMain] j.LocalContainerEntityManagerFactoryBean : Initialized JPA EntityManagerFactory for persistence unit 'default'
2019-03-04 13:03:30.841  INFO 4284 --- [  restartedMain] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: [e-mail]5a01d: startup date [Mon Mar 04 13:03:23 CST 2019]; root of context hierarchy
2019-03-04 13:03:30.930  WARN 4284 --- [  restartedMain] aWebConfiguration$JpaWebMvcConfiguration : spring.jpa.open-in-view is enabled by default. Therefore, database queries may be performed during view rendering. Explicitly configure spring.jpa.open-in-view to disable this warning
2019-03-04 13:03:31.010  INFO 4284 --- [  restartedMain] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/user/findAll]}" onto public java.util.List<com.abc.domain.User> com.abc.web.controller.UserController.findAll()
2019-03-04 13:03:31.016  INFO 4284 --- [  restartedMain] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error]}" onto public org.springframework.http.ResponseEntity<java.util.Map<java.lang.String, java.lang.Object>> org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.error(javax.servlet.http.HttpServletRequest)
2019-03-04 13:03:31.016  INFO 4284 --- [  restartedMain] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error],produces=[text/html]}" onto public org.springframework.web.servlet.ModelAndView org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)
2019-03-04 13:03:31.116  INFO 4284 --- [  restartedMain] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2019-03-04 13:03:31.120  INFO 4284 --- [  restartedMain] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2019-03-04 13:03:31.190  INFO 4284 --- [  restartedMain] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2019-03-04 13:03:31.578  INFO 4284 --- [  restartedMain] o.s.b.d.a.OptionalLiveReloadServer       : LiveReload server is running on port 35729
2019-03-04 13:03:31.677  INFO 4284 --- [  restartedMain] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
2019-03-04 13:03:31.680  INFO 4284 --- [  restartedMain] o.s.j.e.a.AnnotationMBeanExporter        : Bean with name 'dataSource' has been autodetected for JMX exposure
2019-03-04 13:03:31.686  INFO 4284 --- [  restartedMain] o.s.j.e.a.AnnotationMBeanExporter        : Located MBean 'dataSource': registering with JMX server as MBean [com.zaxxer.hikari:name=dataSource,type=HikariDataSource]
2019-03-04 13:03:31.748  INFO 4284 --- [  restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2019-03-04 13:03:31.754  INFO 4284 --- [  restartedMain] com.abc.SpringbootApplicationRunner      : Started SpringbootApplicationRunner in 8.693 seconds (JVM running for 9.522)

访问结果：