Springboot 项目 无法读取resources下的mapper文件夹的.xml文件

之前学习的时候遇到的一个问题

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sqlSessionFactory' defined in class path resource [com/jevin98/demo/config/dao/SessionFactoryConfiguration.class]: Invocation of init method failed; nested exception is org.springframework.core.NestedIOException: Failed to parse mapping resource: 'class path resource [classpath*:/mapper/**.xml]'; nested exception is java.io.FileNotFoundException: class path resource [classpath*:/mapper/**.xml] cannot be opened because it does not exist
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1796) ~[spring-beans-5.2.3.RELEASE.jar:5.2.3.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:595) ~[spring-beans-5.2.3.RELEASE.jar:5.2.3.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:517) ~[spring-beans-5.2.3.RELEASE.jar:5.2.3.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:323) ~[spring-beans-5.2.3.RELEASE.jar:5.2.3.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.2.3.RELEASE.jar:5.2.3.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:321) ~[spring-beans-5.2.3.RELEASE.jar:5.2.3.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) ~[spring-beans-5.2.3.RELEASE.jar:5.2.3.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:860) ~[spring-beans-5.2.3.RELEASE.jar:5.2.3.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:878) ~[spring-context-5.2.3.RELEASE.jar:5.2.3.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550) ~[spring-context-5.2.3.RELEASE.jar:5.2.3.RELEASE]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:747) ~[spring-boot-2.2.4.RELEASE.jar:2.2.4.RELEASE]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) ~[spring-boot-2.2.4.RELEASE.jar:2.2.4.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:315) ~[spring-boot-2.2.4.RELEASE.jar:2.2.4.RELEASE]

主要关注此行：

Failed to parse mapping resource: 'class path resource [classpath*:/mapper/**.xml]'; nested exception is java.io.FileNotFoundException: class path resource [classpath*:/mapper/**.xml] cannot be opened because it does not exist

类路径资源[classpath*:/mapper/**]。不能打开xml，因为它不存在

没道理啊？我的文件目录

resources下明明就有这个mapper文件夹，和这个xml文件，为什么会找不到呢

解决思路：
首先，确定了文件名和application,properties下的路径名没错

其次，检查一下测试的方法

问题可能主要出现在配置mapper上，所以检查SessionFactoryConfiguration

关于sqlSessionFactory：
https://blog.csdn.net/u013412772/article/details/73648537
关于sqlSeesionFactoryBean： https://blog.csdn.net/u013412772/article/details/73648537

仔细检查路径和类基本上都没错，知道看到这行：

sqlSessionFactoryBean.setMapperLocations(resolver.getResource(packageSearchPath));

sqlSessionFactoryBean调用的方法中setMapperLocations可能是导致读取不到mapper资源的原因

关于PathMatchingResourcePatternResolver : https://www.cnblogs.com/loveLands/articles/9863195.html
果然getResource 和 getResources不同

getResource()：
1.从类的根路径下获取文件
getResources():
1.获取所有类路径下的指定文件
可以通过classpath前缀指定，从所有的类路径下获取指定文件，与classpath前缀的区别是classpath前缀只能获取当类路径下的资源文件，而classpath前缀可以获取所有类路径下的资源文件，包括jar包中的。