停止Tomcat服务的时候，log里面报了不少的内存错误信息。经查询是Tomcat6.0.24以后会检测到的问题。

Summary matrix

Leak cause	Detected by tomcat	Fixed by tomcat	Possible enhancements
Custom ThreadLocal class	>=6.0.24	>= 7.0.6
Webapp class instance as ThreadLocal value	>=6.0.24	>= 7.0.6
Webapp class instance indirectly held through a ThreadLocal value	no	>= 7.0.6
ThreadLocal pseudo-leak	>=6.0.24	>= 7.0.6
ContextClassLoader / Threads spawned by webapps	>=6.0.24	In 6.0.24-6.0.26 `TimerThread` are stopped but it may lead to problems. Optional from 6.0.27 with the `clearReferencesStopTimerThreads` flag. Other threads may be stopped with the `clearReferencesStopThreads` flag, but it's unsafe.	Fix the application to stop the thread when the application is stopped
ContextClassLoader / Threads spawned by classes loaded by the common classloader	>=6.0.24	In 6.0.24-6.0.26 `TimerThread` are stopped but it may lead to problems. Optional from 6.0.27 with the `clearReferencesStopTimerThreads` flag. Other threads may be stopped with the `clearReferencesStopThreads` flag, but it's unsafe.	Fix the offending code (set the correct CCL when spawning the thread)
ContextClassLoader / Threads spawned by JRE classes	no	>=6.0.24 pre-spawns some known offenders
static class variables	no	> 6.0.? . Disabled by default with tomcat 7
LogFactory		> 6.0.?
JDBC driver registration	> 6.0.?	> 6.0.?
RMI Target		> 6.0.?

还没升级的情况下，比如ThreadLocal的内存泄漏问题，Tomca7中是用ThreadLocalLeakPreventionListener来解决的。

而Tomcat6.0.24以后可以用Context#clearReferencesThreadLocals=true来解决。

参考URL：http://www.atmarkit.co.jp/fjava/rensai4/tomcat7_03/02.html

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