今天在学习使用Spring Data JPA的时候，将bean和JpaRepository放在了不同的package中，导致无法构建项目，报以下错误：

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'requestMappingHandlerAdapter' defined in class path resource [org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration$EnableWebMvcConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter]: Factory method 'requestMappingHandlerAdapter' threw exception; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'mvcConversionService' defined in class path resource [org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration$EnableWebMvcConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.format.support.FormattingConversionService]: Factory method 'mvcConversionService' threw exception; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'readingListRepository': Invocation of init method failed; nested exception is java.lang.IllegalArgumentException: Not a managed type: class bean.Book

异常是逐层抛出的，所以要定位到错误的地方，应该看最底下的内容，

java.lang.IllegalArgumentException: Not a managed type: class bean.Book

也就是我们没有按照SpringBoot的约定,默认扫描(application.java 入口类相对的兄弟包及其子包)
解决方法1：将bean和JpaRepository放在同一个package中。
解决方法2：在JpaRepository上添加注释，使得它能找到bean

@EntityScan("bean.Book")

这里整合以下常见的配置

@ComponentScan(basePackages = "com.boot.demo.xxx.*.*")
用于扫描@Controller @Service


 @EnableJpaRepositories(basePackages = "com.boot.demo.xxx.*.dao") 
用于扫描Dao @Repository


@EntityScan("com.boot.demo.xxx.*.*")
用于扫描JPA实体类 @Entity

好吧，现在完全不知道spring-boot的文件结构要如何，多创建了几个包，现在各种找不到类，controller也无法配置，明天继续吧。