Details
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Type:
Bug
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Status: Open
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Priority:
Major
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Resolution: Unresolved
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Affects Version/s: 2.3.0
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Fix Version/s: None
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Component/s: Integration: Persistence Support
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Labels:None
Description
JpaFlowExecutionListener stores EntityManager into Flow Scope, assuming it will be Serializable (each object stored into this scope should be Serializable, according to the documentation). This assumption is wrong, EntityManager doesn't extend Serializable, and doesn't have to implement this interface.
Using EclipseLink 2.2 I'm getting following exception in this case:
org.springframework.webflow.execution.repository.snapshot.SnapshotCreationException: Could not serialize flow execution; make sure all objects stored in flow or flash scope are serializable
org.springframework.webflow.execution.repository.snapshot.SerializedFlowExecutionSnapshot.<init>(SerializedFlowExecutionSnapshot.java:75)
org.springframework.webflow.execution.repository.snapshot.SerializedFlowExecutionSnapshotFactory.createSnapshot(SerializedFlowExecutionSnapshotFactory.java:70)
org.springframework.webflow.execution.repository.snapshot.AbstractSnapshottingFlowExecutionRepository.snapshot(AbstractSnapshottingFlowExecutionRepository.java:75)
org.springframework.webflow.execution.repository.impl.DefaultFlowExecutionRepository.putFlowExecution(DefaultFlowExecutionRepository.java:126)
org.springframework.webflow.executor.FlowExecutorImpl.launchExecution(FlowExecutorImpl.java:145)
org.springframework.webflow.mvc.servlet.FlowHandlerAdapter.handle(FlowHandlerAdapter.java:193)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:790)
...
java.io.NotSerializableException: org.eclipse.persistence.internal.jpa.EntityManagerImpl
java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1164)
java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1518)
java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1483)
java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1400)
...
java.util.HashMap.writeObject(HashMap.java:1001)
...
org.springframework.webflow.core.collection.LocalAttributeMap.writeObject(LocalAttributeMap.java:327)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
...
org.springframework.webflow.engine.impl.FlowSessionImpl.writeExternal(FlowSessionImpl.java:154)
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org.springframework.webflow.engine.impl.FlowExecutionImpl.writeExternal(FlowExecutionImpl.java:312)
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org.springframework.webflow.execution.repository.snapshot.SerializedFlowExecutionSnapshot.serialize(SerializedFlowExecutionSnapshot.java:173)
org.springframework.webflow.execution.repository.snapshot.SerializedFlowExecutionSnapshot.<init>(SerializedFlowExecutionSnapshot.java:70)
org.springframework.webflow.execution.repository.snapshot.SerializedFlowExecutionSnapshotFactory.createSnapshot(SerializedFlowExecutionSnapshotFactory.java:70)
org.springframework.webflow.execution.repository.snapshot.AbstractSnapshottingFlowExecutionRepository.snapshot(AbstractSnapshottingFlowExecutionRepository.java:75)
org.springframework.webflow.execution.repository.impl.DefaultFlowExecutionRepository.putFlowExecution(DefaultFlowExecutionRepository.java:126)
org.springframework.webflow.executor.FlowExecutorImpl.launchExecution(FlowExecutorImpl.java:145)
org.springframework.webflow.mvc.servlet.FlowHandlerAdapter.handle(FlowHandlerAdapter.java:193)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:790)
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Lowering the priority since you have the option of merging your flow variables with EntityManager rather than using the persistence-context feature.
Rossen Stoyanchev
added a comment - Lowering the priority since you have the option of merging your flow variables with EntityManager rather than using the persistence-context feature. Rossen: as I understand it correctly, the <persistence-context> feature is broken if the provider does not offer Serializable EntityManger.
What do you mean with "you have the option of merging your flow variables with EntityManager" ?
Is this an alternative somehow? Can you explain this in more detail please with maybe a small example?
I'm facing the same problem with Hibernate 4.0 final and using the Spring embedded database:
Caused by: java.io.NotSerializableException: org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseFactory$EmbeddedDataSourceProxy
As far as I can see, the EmbeddedDatabase is a DataSource, so the EntityManager is trying to serialize a reference to a DataSource, which should be rather transient instead...
Koen Serneels
added a comment - Rossen: as I understand it correctly, the <persistence-context> feature is broken if the provider does not offer Serializable EntityManger.
What do you mean with "you have the option of merging your flow variables with EntityManager" ?
Is this an alternative somehow? Can you explain this in more detail please with maybe a small example?
I'm facing the same problem with Hibernate 4.0 final and using the Spring embedded database:
Caused by: java.io.NotSerializableException: org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseFactory$EmbeddedDataSourceProxy
As far as I can see, the EmbeddedDatabase is a DataSource, so the EntityManager is trying to serialize a reference to a DataSource, which should be rather transient instead... Koen, the flow managed PersistenceContext is indeed stored with other flow-scoped data and by default is expected to be serializable. It makes it easy to implement a "long conversation". However, I've personally ran into cases where persistence provider specific classes are not serializable, which means you can't use the feature. It is possible to turn off snapshotting by setting max-execution-snapshots=0 but that also effectively disables the back button.
The alternative to not using a flow managed PersistenceContext is to obtain and release an EntityManager instance on every request. Objects stored in flow or other scopes longer than request scope would need to be merged with the current EntityManager instance on the last step before being saved.
That said the error you mention above is from a Spring class and maybe within our control to address. Helping to reproduce the issue would accelerate the process if this is important to you. Have you tried using a different database?
Rossen Stoyanchev
added a comment - Koen, the flow managed PersistenceContext is indeed stored with other flow-scoped data and by default is expected to be serializable. It makes it easy to implement a "long conversation". However, I've personally ran into cases where persistence provider specific classes are not serializable, which means you can't use the feature. It is possible to turn off snapshotting by setting max-execution-snapshots=0 but that also effectively disables the back button.
The alternative to not using a flow managed PersistenceContext is to obtain and release an EntityManager instance on every request. Objects stored in flow or other scopes longer than request scope would need to be merged with the current EntityManager instance on the last step before being saved.
That said the error you mention above is from a Spring class and maybe within our control to address. Helping to reproduce the issue would accelerate the process if this is important to you. Have you tried using a different database? 
It looks like there is some thread related to this issue in forum - http://forum.springsource.org/showthread.php?t=59443 - Keith wrote in it: "I would bring this up with the EclipseLink team--perhaps they have this capability factored into their feature roadmap" - This issue has nothing to do with the EclipseLink
- If you demand from the developers to store only Serializable objects to the Flow Scope you have to follow this guidance yourself 
Today we have problem with EclipseLink, tomorrow we will encounter the same with OpenJPA, or any other JPA provider you can imagine (well, except the Hibernate maybe 
)
In short: The reason of this issue is wrong assumption that all implementations of EntityManager should be Serializable, while they don't have to.