最近在做一个项目，今天稍微修改了一些mapper和service、加了一个controller后，项目启动突然警告 + 报错（为了保证可读性加了一些换行）：
2022-02-08 22:28:08.024 WARN 65348 --- [ main] o.a.c.loader.WebappClassLoaderBase :
The web application [ROOT] appears to have started a thread named [logback-1] but has failed to stop it.
This is very likely to create a memory leak. Stack trace of thread:
java.base@11.0.12/jdk.internal.misc.Unsafe.park(Native Method)
java.base@11.0.12/java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:234)
java.base@11.0.12/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2123)
java.base@11.0.12/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1182)
java.base@11.0.12/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
java.base@11.0.12/java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1054)
java.base@11.0.12/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1114)
Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2022-02-08 22:28:08.044 ERROR 65348 --- [ main] o.s.boot.SpringApplication :
Application run failed
org.springframework.beans.factory.UnsatisfiedDependencyException:
Error creating bean with name 'classCacheConfig': Unsatisfied dependency expressed through field 'classService'; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException:
Error creating bean with name 'classServiceImpl': Unsatisfied dependency expressed through field 'baseMapper'; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException:
Error creating bean with name 'classMapper' defined in file [C:\Users\CTC\Desktop\ZKCOURSE\target\classes\com\haotongxue\mapper\ClassMapper.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 [C:\Users\CTC\Desktop\ZKCOURSE\target\classes\com\haotongxue\mapper\xml\UserMapper.xml]'; nested exception is org.apache.ibatis.builder.BuilderException:
Error creating document instance. Cause: org.xml.sax.SAXParseException; lineNumber: 36; columnNumber: 10; The content of element type "mapper" must match "(cache-ref|cache|resultMap*|parameterMap*|sql*|insert*|update*|delete*|select*)+".
除此之外，还显示了其他一些service和mapper的创建Bean失败异常（此处省略），仔细检查了一番各个Bean的写法和使用后，还是找不到问题出现在哪里。对比Git版本后，发现我也没有动过相关Bean，检查了很久才发现原来mapper.xml有个地方多写了一些东西，导致标签无法匹配…
在底部也可以发现mapper标签已经报红：
回想才知道可能在粘贴方法名的时候不小心。但是idea中的xxxMapper.xml文件却没有报红，特别是我们在日常code的时候，很容易忽略这些藏在文件里的报红细节。
将这串多出来的字母删去后，一切恢复正常。
其实在报错信息的一些列“Caused by…”中，除了前面的一大堆
Caused by: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name ‘xxx’
信息外，在底部还有一串：
Caused by: org.springframework.core.NestedIOException: Failed to parse mapping resource: ‘file [C:\Users\CTC\Desktop\xxxxx\target\classes\com\xxxxx\mapper\xml\UserMapper.xml]’;
还有一串：
Caused by: org.apache.ibatis.builder.BuilderException: Error creating
document instance. Cause: org.xml.sax.SAXParseException; lineNumber:
36; columnNumber: 10; The content of element type “mapper” must match
从中可以看出，其实编译器已经提醒我们错误具体在哪个文件里了，甚至行数和列数也给我们了（虽然是不准的），只是被我忽略了…
但是为什么会出现那么多Bean创建失败的情况呢？报错的绝大多数Bean也没有直接引用这个mapper组件，而且还出现了内存泄漏（Memory leak）的多条警告，欢迎各位大佬交流指教o(╥﹏╥)o