Mapped Statements collection does not contain value for

Mapped Statements collection does not contain value for what class and method are behind:
There are several reasons for the error:
1. The namespace is not added to
mapper.xml 2. The method in mapper.xml does not correspond to the method of the interface mapper
3. mapper.xml is not added to mybatis-config.xml (that is, the general configuration file), except for the package path where the mapper file is configured.
4. The mapper.xml file name is not the same as the written mapper name.