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Memcached存储枚举

今天发布线上碰到一个小问题，Memcached存储的数据类型包括枚举的时候，当修改枚举的包路径之后，会出现问题。 异常信息如下，比较直观，就是数据的反序列化失败：

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[2015-11-23 18:04:45 ERROR net.rubyeye.xmemcached.transcoders.BaseSerializingTranscoder:113] Caught CNFE decoding 944 bytes of data
java.lang.ClassNotFoundException: Xxx.Xxx.Xxx.Xxx.RoomStatus
        at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1702) ~[catalina.jar:7.0.47]
        at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1547) ~[catalina.jar:7.0.47]
        at net.rubyeye.xmemcached.transcoders.BaseSerializingTranscoder$1.resolveClass(BaseSerializingTranscoder.java:102) ~[xmemcached-1.4.1.jar:na]
        at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1612) ~[na:1.7.0_45]
        at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1517) ~[na:1.7.0_45]
        at java.io.ObjectInputStream.readEnum(ObjectInputStream.java:1725) ~[na:1.7.0_45]
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1347) ~[na:1.7.0_45]
        at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1990) ~[na:1.7.0_45]
        at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1915) ~[na:1.7.0_45]
        at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1798) ~[na:1.7.0_45]
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350) ~[na:1.7.0_45]
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370) ~[na:1.7.0_45]
        at java.util.ArrayList.readObject(ArrayList.java:771) ~[na:1.7.0_45]
        at sun.reflect.GeneratedMethodAccessor41.invoke(Unknown Source) ~[na:na]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.7.0_45]
        at java.lang.reflect.Method.invoke(Method.java:606) ~[na:1.7.0_45]
        at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:1017) ~[na:1.7.0_45]
        at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1893) ~[na:1.7.0_45]
        at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1798) ~[na:1.7.0_45]
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350) ~[na:1.7.0_45]
        at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1990) ~[na:1.7.0_45]
        at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1915) ~[na:1.7.0_45]
        at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1798) ~[na:1.7.0_45]
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350) ~[na:1.7.0_45]
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370) ~[na:1.7.0_45]
        at net.rubyeye.xmemcached.transcoders.BaseSerializingTranscoder.deserialize(BaseSerializingTranscoder.java:106) ~[xmemcached-1.4.1.jar:na]
        at net.rubyeye.xmemcached.transcoders.SerializingTranscoder.decode0(SerializingTranscoder.java:92) [xmemcached-1.4.1.jar:na]
        at net.rubyeye.xmemcached.transcoders.SerializingTranscoder.decode(SerializingTranscoder.java:86) [xmemcached-1.4.1.jar:na]
        at net.rubyeye.xmemcached.XMemcachedClient.fetch0(XMemcachedClient.java:630) [xmemcached-1.4.1.jar:na]
        at net.rubyeye.xmemcached.XMemcachedClient.get0(XMemcachedClient.java:1030) [xmemcached-1.4.1.jar:na]
        at net.rubyeye.xmemcached.XMemcachedClient.get(XMemcachedClient.java:988) [xmemcached-1.4.1.jar:na]
        at net.rubyeye.xmemcached.XMemcachedClient.get(XMemcachedClient.java:999) [xmemcached-1.4.1.jar:na]

场景如下：

  1. Memcached已经有数据，数据中包含RoomStatus数据；
  2. 修改了枚举的包路径，发布线上；
  3. 从Cache中读取之前的数据会出现枚举反序列化异常；

在本地代码中重现了一下问题，并看了一下使用枚举的情况下其他可能处心问题的场景，结论如下（前提是Cache中已经存在使用RoomStatus数据）：

  1. 修改包路径，会导致get数据反序列化失败，java.lang.ClassNotFoundException: Xxx.Xxx.Xxx.Xxx.RoomStatus；
  2. RoomStatus增加项，正常；
  3. RoomStatus减少项(已Cache数据中未使用到的项)，正常；
  4. RoomStatus减少项(已Cache数据中使用到的项)，异常：enum constant Xxx does not exist in Xxx.Xxx.Xxx.Xxx.RoomStatus；

综上，在Memcached中cache包含枚举的数据时候，建议如下：

  1. 不要修改枚举的包路径；
  2. 不要删除枚举中的数据；

这些序列化和反序列化的逻辑再XMemcached客户端实现的。详见SerializingTranscoder类，包含数据的encode和decode逻辑。再使用Memcached的时候也可以使用