项目场景：

springBoot项目build编译成功，maven依赖都没问题，项目启动run服务的时候报异常：

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'demoUserController': Unsatisfied dependency expressed through field 'demoUserService'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'demoUserServiceImpl': Injection of resource dependencies failed; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'demoUserMapper' defined in file [E:\workspace\financial-attendance\target\classes\com\luntek\financialattendance\mapper\DemoUserMapper.class]: Unsatisfied dependency expressed through bean property 'sqlSessionFactory'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sqlSessionFactory' defined in class path resource [com/baomidou/mybatisplus/autoconfigure/MybatisPlusAutoConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.apache.ibatis.session.SqlSessionFactory]: Factory method 'sqlSessionFactory' threw exception; nested exception is org.springframework.core.NestedIOException: Failed to parse mapping resource: 'file [E:\workspace\financial-attendance\target\classes\mapper\StProjectApproveMapper.xml]'; nested exception is org.apache.ibatis.builder.BuilderException: Error creating document instance.  Cause: org.xml.sax.SAXParseException; lineNumber: 104; columnNumber: 28; 元素类型 "select" 必须后跟属性规范 ">" 或 "/>"。

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问题描述和分析

问题已经很清楚了，创建mapper.xml文件实例失败，也指出了是`\mapper\StProjectApproveMapper.xml`这个xml文件的`lineNumber: 104; columnNumber: 28`104行28列有问题

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解决方案：

已经定位到写select语句的时候，设置`parameterType`参数类型的时候是少了个空格。补上即可。 

总结：

springBoot项目build编译是不会检查xml的语法，mapper.xml文件是项目运行时java虚拟机根据mybaits创建文件实例的时候检查报错，遇到问题不用慌，错误日志看起来。