spring.datasource.schema で指定するパスには classpath: を付ける

## Spring Boot 起動時にエラーが発生

「InvalidConfigurationPropertyValueException: Property spring.datasource.schema with value 'ServletContext resource [/schema.sql]' is invalid: The specified resource does not exist.」とのこと。

```
org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'sampleController': Unsatisfied dependency expressed through field 'service'; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'sampleService': Unsatisfied dependency expressed through field 'jdbcTemplate'; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'jdbcTemplate' defined in class path resource [org/springframework/boot/autoconfigure/jdbc/JdbcTemplateConfiguration.class]: Unsatisfied dependency expressed through method 'jdbcTemplate' parameter 0; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource' defined in class path resource [org/springframework/boot/autoconfigure/jdbc/DataSourceConfiguration$Hikari.class]: Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.boot.autoconfigure.jdbc.DataSourceInitializerInvoker': Invocation of init method failed; nested exception is org.springframework.boot.context.properties.source.InvalidConfigurationPropertyValueException: Property spring.datasource.schema with value 'ServletContext resource [/schema.sql]' is invalid: The specified resource does not exist.
(中略)
Caused by: org.springframework.boot.context.properties.source.InvalidConfigurationPropertyValueException: Property spring.datasource.schema with value 'ServletContext resource [/schema.sql]' is invalid: The specified resource does not exist.
	at org.springframework.boot.autoconfigure.jdbc.DataSourceInitializer.getResources(DataSourceInitializer.java:163) ~[spring-boot-autoconfigure-2.2.0.M5.jar!/:2.2.0.M5]
	at org.springframework.boot.autoconfigure.jdbc.DataSourceInitializer.getScripts(DataSourceInitializer.java:146) ~[spring-boot-autoconfigure-2.2.0.M5.jar!/:2.2.0.M5]
	at org.springframework.boot.autoconfigure.jdbc.DataSourceInitializer.createSchema(DataSourceInitializer.java:93) ~[spring-boot-autoconfigure-2.2.0.M5.jar!/:2.2.0.M5]
	at org.springframework.boot.autoconfigure.jdbc.DataSourceInitializerInvoker.afterPropertiesSet(DataSourceInitializerInvoker.java:62) ~[spring-boot-autoconfigure-2.2.0.M5.jar!/:2.2.0.M5]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1863) ~[spring-beans-5.2.0.RC1.jar!/:5.2.0.RC1]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1800) ~[spring-beans-5.2.0.RC1.jar!/:5.2.0.RC1]
	... 77 common frames omitted
```

## ファイル名の前に「classpath:」を付けて解決

application.properties の spring.datasource.schema や spring.datasource.data で指定するファイル名の前には「classpath:」を付ける必要がある。

```application.properties
spring.datasource.url=jdbc:mysql://localhost:3306/testdb
spring.datasource.username=java
spring.datasource.password=cafebabe
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.initialization-mode=always
spring.datasource.schema=classpath:schema.sql
spring.datasource.data=classpath:data.sql
spring.datasource.sql-script-encoding=utf-8
```

## 参考資料
- [Property spring\.datasource\.schema with value 'class path resource \[schema\-mysql\.sql\]' is invalid: The specified resource does not exist \- Stack Overflow](https://stackoverflow.com/questions/53672875/property-spring-datasource-schema-with-value-class-path-resource-schema-mysql)
- [Spring Boot Reference Documentation - Appendices - Appendix A: Common application properties](https://docs.spring.io/spring-boot/docs/2.2.0.M5/reference/html/appendix.html#appendix)