Tomcat-7.0.47-x86 启动时抛异常 java.io.NotSerializableException

前段时间做了壹個小的 Web 应用，跑在 Tomcat-7.0.47-x86 上，结果发现 Tomcat 容器启动时偶尔会抛出 java.io.NotSerializableException 异常，但是把 Tomcat 关闭之后再重启问题就不复存在。具体的错误堆栈信息如下所示：

严重: IOException while loading persisted sessions: java.io.WriteAbortedException: writing aborted; java.io.NotSerializableException: com.shch.pats.service.AsynTradeExecutionServiceBean
java.io.WriteAbortedException: writing aborted; java.io.NotSerializableException: com.shch.pats.service.AsynTradeExecutionServiceBean
	at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1352)
	at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1989)
	at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1913)
	at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1796)
	at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1348)
	at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370)
	at org.apache.catalina.session.StandardSession.readObject(StandardSession.java:1597)
	at org.apache.catalina.session.StandardSession.readObjectData(StandardSession.java:1062)
	at org.apache.catalina.session.StandardManager.doLoad(StandardManager.java:284)
	at org.apache.catalina.session.StandardManager.load(StandardManager.java:204)
	at org.apache.catalina.session.StandardManager.startInternal(StandardManager.java:491)
	at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
	at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5443)
	at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
	at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1559)
	at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1549)
	at java.util.concurrent.FutureTask.run(FutureTask.java:262)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:724)

在网上查了下，原来是因为我的壹個 Bean 的声明中没有实现接口 java.io.Serializable，只要在类的定义上添加上这句，问题就得到了圆满解决，Tomcat 也不会再抛出异常了。就像下面这样：

public class AsynTradeExecutionServiceBean implements java.io.Serializable {
...
}

真是個奇怪的问题，序列化这东西还真是有点冒名其妙，弄不明白。另外我重点参考了 StackOverflow 的帖子： What causes a NotSerializableException in Tomcat 7，老外们在跟帖中是这麽说的：

1. Don't store non-serializable objects in the users session (generally a good practice).
2. Make your UserDAO serializable. Probably involves implementing the Serializable interface and marking your hibernateTemplate as transient as i don't think that HibernateTemplate is, in itself, serializable. You may have to add some code that re-initialize the hibernateTemplate on deserialization if you really want it to work.
3. Don't have Tomcat serializing sessions (add <Manager pathname="" /> to the context.xml, either in your own app or in the global tomcat context.xml in the conf/ directory, inside the <Context> element. This might be the best course of action for you, unless you really need sessions to be persisted across restarts.

这问题算是暂时解决了，有空再回来详细研究研究。