在公司项目里想要在前端通过nginx将请求负载均衡，而后台的几组tomcat的session通过memcached(non-sticky模式)进行统一管理，这几组tomcat部署的web app是同一应用，session的变化要统一，项目组最后采用memcached-session-manager来对tomcat的session进行管理。

session的序列化方案官方推荐的有4种

1. java serialization
2. msm-kryo-serializer
3. msm-javolution-serializer
4. msm-xstream-serializer
   

关于这几种，官方也给出了比较:

• Java serialization is very robust and a
  proven technology. The biggest disadvantage IMHO is that different
  class versions cannot be handled.
• Kryo is an extremely fast binary serialization library. In the popular thrift-protobuf-compare benchmark it's one of the fastest serialization toolkits - and it differs from the fastest in that it does NOT need
  a schema definition of serialized data, which is a requirement for
  serialization arbitrary session data. A disadvantage of using kryo based
  serialization is that it's binary - you just cannot look how the
  serialized object graph looks like. This is my favorite serialization
  strategy, just because of its great performance.
• Javolution is
  a very good and fast xml binding toolkit. The reflection part is
  written by me and adds the bits that are actually binding POJOs to xml.
  It is covered well with unit tests, however I cannot guarantee that
  there's no issue left to solve (actually this serialization strategy was
  in use in my own projects, now replaced by kryo based serialization).
• XStream based
  serialization should be very robust as this is an often used java
  object binding library. The biggest disadvantage IMHO is the relatively
  bad performance.

要注意的是javolution是唯一支持copyCollectionsForSerialization="true"时对能对线程不安全的collection进行序列化特性的，其他的方案要对序列化线程不安全的collection时特别处理，性能最好的序列化方案是Kryo。

网上有一些例子都是关于Javolution的，我个人倾向于使用Kryo，至于序列化出现的问题还可以自己解决，不过先使用java IO来配置，先用起来，以后再慢慢优化，换成Kryo。

直接在$CATALINA_HOME/lib/下添加memcached-2.5.jar和memcached-session-manager-1.4.0.jar，然后对$CATALINA_HOME/conf/server.xml修改相应的配置

由于项目对session 管理模式是non-sticky的，所以不配置failoverNodes，任何一个web工程对session的修改要及时更新到memcache上，所以sessionBackupTimeout为0(不同的应用有不同的配置，这样配置是符合我现在这个项目要求的)。