tomcat启动加载类的顺序

今天在写一个用java发email的程序的一点总结：
在tomcat如果要使用mail session,必须保证activation.jar和mail.jar在同一个级别的classpath tomcat5默认是在${CATALINA_HOME}common/lib/下放了mail.jar,但是没有activation.jar，就这一点害的我今天忙了半天。
下面是tomcat启动加载类的顺序，记住在container环境下，类是有层次的，我今天就是把activation.jar 放在了WEB-INF/lib下，mail.jar在${CATALINA_HOME}common/lib/下,结果邮件怎么也发不出去。

Bootstrap: uses JVM classes & looks in $JAVA_HOME/jre/lib/ext
         |
      System:    uses $CATALINA_HOME/bin/bootstrap.jar
         |       and  $JAVA_HOME/lib/tools.jar
         |
      Common:    uses $CATALINA_HOME/common/lib
        /  \     and $CATALINA_HOME/common/classes
       /    \    and $CATALINA_HOME/common/endorsed
      /      \   >> jsp and servlet API jars are here
     /        +---------------------------------+
    /                                           |
Catalina:  uses $CATALINA_HOME/server/lib       |
           and $CATALINA_HOME/server/classes    |
           >> catalina.jar is here              |
                                             Shared: uses 
$CATALINA_BASE/shared/lib
                                               / \    and 
$CATALINA_BASE/shared/classes
                                              /   \
                                         Webapp1  Webapp2 ... <--- **GREEDY** 
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