Tomcat6.0的Thisisverylikelytocreateamemoryleak异常

從Apache Tomcat 5.5升級到6.0，通常不用太大的修改，原有的Web Application就能繼續運作。不過在server.xml中設定MySQL Datasource，卻出現一串惱人的警告訊息：

2010/8/6 下午 01:54:11 org.apache.catalina.loader.WebappClassLoader clearReferencesJdbc  
嚴重的: The web application [/] registered the JBDC driver [com.mysql.jdbc.Driver] but failed to unregister it when the web application was stopped. To prevent a memory leak, the JDBC Driver has been forcibly unregistered.  
2010/8/6 下午 01:54:11 org.apache.catalina.loader.WebappClassLoader clearReferencesThreads  
嚴重的: The web application [/] appears to have started a thread named [Timer-0] but has failed to stop it. This is very likely to create a memory leak.  
2010/8/6 下午 01:54:11 org.apache.catalina.loader.WebappClassLoader clearReferencesThreads  
嚴重的: The web application [/] appears to have started a thread named [MySQL Statement Cancellation Timer] but has failed to stop it. This is very likely to create a memory leak.

更新MySQL Connector/J至最新版也沒用，似乎是Tomcat 6.0對於Memory Leak的防範變得比較雞婆智慧，才會多了這樣的警告。

既然被列為嚴重程度的警告，當然就不能視而不見，解決的方法並不難，只是要把原本設定在區段中的搬到，修改方式如下。

1. 將<Resource name="jdbc/NAME" auth="Container" type="javax.sql.DataSource" ... /> 整塊剪下，再貼到 <GlobalNamingResources> ... </GlobalNamingResources> 之間。

2. 在原本Resource標籤的位置加入<ResourceLink global="jdbc/NAME" name="jdbc/NAME" type="javax.sql.DataSource" />

2011-11-09 10:40 tomcat memory leak 在tomcat（版本6.0.33）的 catalina.out中发现大量memory leak的日志

org.apache.catalina.loader.WebappClassLoader clearThreadLocalMap

SEVERE: The web application [] created a ThreadLocal with key of type [com.opensymphony.xwork2.inject.ContainerImpl$10] (value [com.opensymphony.xwork2.inject.ContainerImpl$10@2618d45f]) and a value of type [java.lang.Object[]] (value [[Ljava.lang.Object;@51dce88]) but failed to remove it when the web application was stopped. This is very likely to create a memory leak.

这个是由于tomcat6.0.24以后的版本有加一个监控memory leak的listener 在tomcathome/conf/server.xml

<!-- Prevent memory leaks due to use of particular java/javax APIs-->

<Listener className="org.apache.catalina.core.JreMemoryLeakPreventionListener" />

但是这个监控有bug才导致的误报

解决方式任选一种 1 把tomcat降级为6.0.24以下的版本

2 将tomcat升级为7.0.6以上的版本

3 在server.xml中去掉JreMemoryLeakPreventionListener的listener