title: Hibernate + EhCache = java.io.NotSerializableException
body: <p>I'm doing load test now. After approximate 900 requests i got this error:</p>
  
  <pre><code>[ 03.08.10 11:49:00.465] [Store org.hibernate.cache.StandardQueryCache Spool Thread] ERROR net.sf.ehcache.store.DiskStore  - org.hibernate.cache.StandardQueryCacheCache: Failed to write element to disk 'sql: select hotelfeatu0_.name as col_0_0_ from feature hotelfeatu0_ where hotelfeatu0_.class='org.company.domains.HotelFeatures' and hotelfeatu0_.lang=? and hotelfeatu0_.hotel_id=?; parameters: ; named parameters: {ht=100: 'Hotel', lng=en}'. Initial cause was org.company.domains.Hotel
  java.io.NotSerializableException: org.company.domains.Hotel
      at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1156)
      at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1509)
      at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1474)
      at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1392)
      at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1150)
      at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:326)
      at java.util.HashMap.writeObject(HashMap.java:1001)
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
      at java.lang.reflect.Method.invoke(Method.java:597)
      at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:945)
      at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1461)
      at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1392)
      at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1150)
      at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1509)
      at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1474)
      at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1392)
      at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1150)
      at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1509)
      at java.io.ObjectOutputStream.defaultWriteObject(ObjectOutputStream.java:416)
      at net.sf.ehcache.Element.writeObject(Element.java:729)
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
      at java.lang.reflect.Method.invoke(Method.java:597)
      at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:945)
      at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1461)
      at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1392)
      at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1150)
      at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:326)
      at net.sf.ehcache.util.MemoryEfficientByteArrayOutputStream.serialize(MemoryEfficientByteArrayOutputStream.java:75)
      at net.sf.ehcache.store.DiskStore.serializeElement(DiskStore.java:781)
      at net.sf.ehcache.store.DiskStore.writeElement(DiskStore.java:735)
      at net.sf.ehcache.store.DiskStore.writeOrReplaceEntry(DiskStore.java:729)
      at net.sf.ehcache.store.DiskStore.flushSpool(DiskStore.java:703)
      at net.sf.ehcache.store.DiskStore.throwableSafeFlushSpoolIfRequired(DiskStore.java:671)
      at net.sf.ehcache.store.DiskStore.spoolAndExpiryThreadMain(DiskStore.java:640)
      at net.sf.ehcache.store.DiskStore.access$900(DiskStore.java:68)
      at net.sf.ehcache.store.DiskStore$SpoolAndExpiryThread.run(DiskStore.java:1110)
  </code></pre>
  
  <p>Here is my ehcache.xml:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;ehcache xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="ehcache.xsd" updateCheck="false"&gt;
  
      &lt;diskStore path="java.io.tmpdir/sweethome"/&gt;
  
      &lt;defaultCache
              maxElementsInMemory="10000"
              eternal="false"
              timeToIdleSeconds="120"
              timeToLiveSeconds="120"
              overflowToDisk="true"
              maxElementsOnDisk="10000000"
              diskPersistent="false"
              diskExpiryThreadIntervalSeconds="120"
              memoryStoreEvictionPolicy="LRU"
      /&gt;
  
      &lt;cache
                  name="org.hibernate.cache.StandardQueryCache"
                  maxElementsInMemory="5"
                  eternal="false"
                  timeToLiveSeconds="120"
                  overflowToDisk="true"
      /&gt;
  
  &lt;/ehcache&gt;
  </code></pre>
  
  <p>Hibernate config:</p>
  
  <pre><code>hibernate {
      cache.use_second_level_cache=true
      cache.use_query_cache=true
      cache.provider_class='org.hibernate.cache.EhCacheProvider'
      connection.useUnicode=true
      connection.characterEncoding='UTF-8'
      dialect = 'org.hibernate.dialect.MySQL5InnoDBDialect'
  }
  </code></pre>