Springboot 項目 無法讀取resources下的mapper文件夾的.xml文件

之前學習的時候遇到的一個問題

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]

主要關注此行：

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

類路徑資源[classpath*:/mapper/**]。不能打開xml，因為它不存在

沒道理啊？我的文件目錄

resources下明明就有這個mapper文件夾，和這個xml文件，為什么會找不到呢

解決思路：
首先，確定了文件名和application,properties下的路徑名沒錯

其次，檢查一下測試的方法

問題可能主要出現在配置mapper上，所以檢查SessionFactoryConfiguration

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

仔細檢查路徑和類基本上都沒錯，知道看到這行：

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

sqlSessionFactoryBean調用的方法中setMapperLocations可能是導致讀取不到mapper資源的原因

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

getResource()：
1.從類的根路徑下獲取文件
getResources():
1.獲取所有類路徑下的指定文件
可以通過classpath前綴指定，從所有的類路徑下獲取指定文件，與classpath前綴的區別是classpath前綴只能獲取當類路徑下的資源文件，而classpath前綴可以獲取所有類路徑下的資源文件，包括jar包中的。