java.lang.NoClassDefFoundError: javax/mail/internet/AddressException解决

初学log4j，用于监听系统运行状态，因为系统要一直运行，所以用了发送邮件通知功能，结果报错了，如下：

Exception in thread "Animation Thread" java.lang.NoClassDefFoundError: javax/mail/internet/AddressException

at java.lang.Class.getDeclaredConstructors0(Native Method)

at java.lang.Class.privateGetDeclaredConstructors(Unknown Source)

at java.lang.Class.getConstructor0(Unknown Source)

at java.lang.Class.newInstance0(Unknown Source)

at java.lang.Class.newInstance(Unknown Source)

at org.apache.log4j.helpers.OptionConverter.instantiateByClassName(OptionConverter.java:336)

at org.apache.log4j.helpers.OptionConverter.instantiateByKey(OptionConverter.java:123)

at org.apache.log4j.PropertyConfigurator.parseAppender(PropertyConfigurator.java:752)

at org.apache.log4j.PropertyConfigurator.parseCategory(PropertyConfigurator.java:735)

at org.apache.log4j.PropertyConfigurator.parseCatsAndRenderers(PropertyConfigurator.java:639)

at org.apache.log4j.PropertyConfigurator.doConfigure(PropertyConfigurator.java:504)

at org.apache.log4j.PropertyConfigurator.doConfigure(PropertyConfigurator.java:395)

at org.apache.log4j.PropertyConfigurator.configure(PropertyConfigurator.java:403)

at source.MapDistribution.setup(MapDistribution.java:84)

at processing.core.PApplet.handleDraw(Unknown Source)

at processing.core.PApplet.run(Unknown Source)

at java.lang.Thread.run(Unknown Source)

Caused by: java.lang.ClassNotFoundException: javax.mail.internet.AddressException

at java.net.URLClassLoader$1.run(Unknown Source)

at java.security.AccessController.doPrivileged(Native Method)

at java.net.URLClassLoader.findClass(Unknown Source)

at java.lang.ClassLoader.loadClass(Unknown Source)

at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)

at java.lang.ClassLoader.loadClass(Unknown Source)

... 17 more

傻傻的找了很多资料，尝试了未果。后来想起来以前做的一个项目也用到mail功能，当时好像导入了一个库的。在现在项目里找了半天，GOD！居然没有！去下了javamail，把库导入到项目里，OK，解决！

折腾了半天，原来是这种小错误，呜呼哀哉……