tomcat启动报错： 严重: createMBeans: Throwable java.lang.NullPointerException

tomcat启动报错如下：
2014-12-17 15:27:34 org.apache.catalina.mbeans.ServerLifecycleListener createMBeans
严重: createMBeans: Throwable java.lang.NullPointerException
        at org.apache.catalina.mbeans.MBeanUtils.createObjectName(MBeanUtils.java:1086)
        at org.apache.catalina.mbeans.MBeanUtils.createMBean(MBeanUtils.java:504)
        at org.apache.catalina.mbeans.ServerLifecycleListener.createMBeans(ServerLifecycleListener.java:570)
        at org.apache.catalina.mbeans.ServerLifecycleListener.createMBeans(ServerLifecycleListener.java:366)
        at org.apache.catalina.mbeans.ServerLifecycleListener.createMBeans(ServerLifecycleListener.java:535)
        at org.apache.catalina.mbeans.ServerLifecycleListener.createMBeans(ServerLifecycleListener.java:498)
        at org.apache.catalina.mbeans.ServerLifecycleListener.createMBeans(ServerLifecycleListener.java:656)
        at org.apache.catalina.mbeans.ServerLifecycleListener.createMBeans(ServerLifecycleListener.java:628)
        at org.apache.catalina.mbeans.ServerLifecycleListener.createMBeans(ServerLifecycleListener.java:278)
        at org.apache.catalina.mbeans.ServerLifecycleListener.lifecycleEvent(ServerLifecycleListener.java:129)
        at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:142)
        at org.apache.catalina.core.StandardServer.start(StandardServer.java:747)
        at org.apache.catalina.startup.Catalina.start(Catalina.java:595)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:289)
        at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:414)
2014-12-17 15:27:34 org.apache.catalina.core.StandardService start

解决办法：
tomcat的配置文件server.xml里有一行配置修改如下：

<Context debug="0" crossContext="true" reloadable="true" docBase="D:\\product\\ssmm_demo\\target\\ssmm_demo"/>
改成
<Context debug="0" crossContext="true" reloadable="true" docBase="D:\\product\\ssmm_demo\\target\\ssmm_demo" path=""/>

缺一个path，加上即可。

下面顺便介绍一下这个配置里的各个属性的含义：
path 指出你的项目访问路径
docBase 指出你的war包存放路径
debug 为设定debug的等级0提供最少的信息,9提供最多的信息
reloadable=true时 当web.xml或者class有改动的时候都会自动重新加载不需要从新启动服务
crosscontext="true"表示配置的不同context共享一个session

知道了每个配置的含义，自然就不会遗漏掉了。