Idea使用外置tomcat启动SpringBoot项目报错：sun.misc.Unsafe.park(Native Method)和InstanceAlreadyExistsException

首先说明问题，使用Application也就是内置tomcat启动项目一切正常，但使用外置tomcat启动会报错，那就肯定是项目启动环境配置问题，

其中有两个错误：

第一个错误：

18-Jan-2019 10:26:00.250 警告 [ContainerBackgroundProcessor[StandardEngine[Catalina]]] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesJdbc The web application [ROOT] registered the JDBC driver [com.alibaba.druid.proxy.DruidDriver] but failed to unregister it when the web application was stopped. To prevent a memory leak, the JDBC Driver has been forcibly unregistered.
18-Jan-2019 10:26:00.250 警告 [ContainerBackgroundProcessor[StandardEngine[Catalina]]] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesJdbc The web application [ROOT] registered the JDBC driver [org.postgresql.Driver] but failed to unregister it when the web application was stopped. To prevent a memory leak, the JDBC Driver has been forcibly unregistered.
18-Jan-2019 10:26:00.252 警告 [ContainerBackgroundProcessor[StandardEngine[Catalina]]] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [ROOT] appears to have started a thread named [commons-pool-evictor-thread] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
 sun.misc.Unsafe.park(Native Method)
 java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
 java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2078)
 java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1093)
 java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:809)
 java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
 java.lang.Thread.run(Thread.java:748)

第二个错误：

18-Jan-2019 10:26:23.733 严重 [ContainerBackgroundProcessor[StandardEngine[Catalina]]] org.apache.catalina.core.StandardContext.reload Exception starting Context with name []
 org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[]]
	at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:167)
	at org.apache.catalina.core.StandardContext.reload(StandardContext.java:3859)
	at org.apache.catalina.loader.WebappLoader.backgroundProcess(WebappLoader.java:291)
	at org.apache.catalina.core.StandardContext.backgroundProcess(StandardContext.java:5634)
	at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1392)
	at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1396)
	at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1396)
	at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.run(ContainerBase.java:1364)
	at java.lang.Thread.run(Thread.java:748)
Caused by: org.springframework.jmx.export.UnableToRegisterMBeanException: Unable to register MBean [com.alibaba.druid.filter.stat.StatFilter@4fd6301b] with key 'statFilter'; nested exception is javax.management.InstanceAlreadyExistsException: com.alibaba.druid.filter.stat:name=statFilter,type=StatFilter
	at org.springframework.jmx.export.MBeanExporter.registerBeanNameOrInstance(MBeanExporter.java:628)
	at org.springframework.jmx.export.MBeanExporter.registerBeans(MBeanExporter.java:550)
	at org.springframework.jmx.export.MBeanExporter.afterSingletonsInstantiated(MBeanExporter.java:432)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:781)
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:867)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:543)
	at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:122)
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:693)
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:360)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:303)
	at org.springframework.boot.web.support.SpringBootServletInitializer.run(SpringBootServletInitializer.java:154)
	at org.springframework.boot.web.support.SpringBootServletInitializer.createRootApplicationContext(SpringBootServletInitializer.java:134)
	at org.springframework.boot.web.support.SpringBootServletInitializer.onStartup(SpringBootServletInitializer.java:87)
	at org.springframework.web.SpringServletContainerInitializer.onStartup(SpringServletContainerInitializer.java:169)
	at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5267)
	at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
	... 8 more
Caused by: javax.management.InstanceAlreadyExistsException: com.alibaba.druid.filter.stat:name=statFilter,type=StatFilter
	at com.sun.jmx.mbeanserver.Repository.addMBean(Repository.java:437)
	at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.registerWithRepository(DefaultMBeanServerInterceptor.java:1898)
	at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.registerDynamicMBean(DefaultMBeanServerInterceptor.java:966)
	at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.registerObject(DefaultMBeanServerInterceptor.java:900)
	at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.registerMBean(DefaultMBeanServerInterceptor.java:324)
	at com.sun.jmx.mbeanserver.JmxMBeanServer.registerMBean(JmxMBeanServer.java:522)
	at org.springframework.jmx.support.MBeanRegistrationSupport.doRegister(MBeanRegistrationSupport.java:195)
	at org.springframework.jmx.export.MBeanExporter.registerBeanInstance(MBeanExporter.java:674)
	at org.springframework.jmx.export.MBeanExporter.registerBeanNameOrInstance(MBeanExporter.java:618)
	... 23 more

针对解决办法：首先第一个错误引起的原因是因为访问地址错误，在访问本地地址时会发现会添加一个后缀，比如原本首页访问应该是是localhost:8080,而tomcat启动项目运行后项目启动却是"localhost:8080/项目名"，该处进行修改，在tomcat处配置如下，将后缀去掉

 然后在tomcat文件夹下webapps内将项目文件删除，该项目文件不删除下次启动将会报该处的错误

针对第二个错误修改：修改tomcat下的conf文件中server.xml文件,在文件最后将Context标签下的docBase内容改为“/”，如下图

改完之后冲洗项目即可

说明：改配置完成之后，想要找到项目加载后的文件(前提是tomcat配置时配置的是tomcat启动会加载文件)，可访问webapps下的ROOT文件夹，想要使用，创建一个名为项目名的文件夹，将ROOT中的文件拷贝进去即可使用

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