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Do I have to use Serializable for JPA and Hibernate entities? Entities do not need to be Serializable. However, if you want to serialize them, you can safely implement Serializable.
Implement the Serializable interface when you want to be able to convert an instance of a class into a series of bytes or when you think that a Serializable object might reference an instance of your class. Serializable classes are useful when you want to persist instances of them or send them over a wire.
Serialization in Java allows us to convert an Object to stream that we can send over the network or save it as file or store in DB for later usage. Deserialization is the process of converting Object stream to actual Java Object to be used in our program.
Serialization and Deserialization in Spring Boot. In terms of Rest, APIs Serialization is what Spring boot does when it converts the Java object to JSON object, and similarly, Deserialization is when it converts JSON object to Java object.
According to JPA Spec:
If an entity instance is to be passed by value as a detached object (e.g., through a remote interface), the entity class must implement the Serializable interface.
"JSR 220: Enterprise JavaBeansTM,Version 3.0 Java Persistence API Version 3.0, Final Release May 2, 2006"
You need your entities to be Serializable if you need to transfer them over-the-wire (serialize them to some other representation), store them in http session (which is in turn serialized to hard disk by the servlet container), etc.
Just for the sake of persistence, Serializable is not needed, at least with Hibernate.
But it is a best practice to make them Serializable.
This usually happens if you mix HQL and native SQL queries. In HQL, Hibernate maps the types you pass in to whatever the DB understands. When you run native SQL, then you must do the mapping yourself. If you don't, then the default mapping is to serialize the parameter and send it to the database (in the hope that it does understand it).
According to the JPA specification, an entity should implement Serializable only if it needs to be passed from one JVM to another or if the entity is used by a Stateful Session Bean which needs to be passivated by the EJB container.
If an entity instance is to be passed by value as a detached object (e.g., through a remote interface), the entity class must implement the
Serializableinterface.
Hibernate only requires that entity attributes are Serializable, but not the entity itself.
However, implementing the JPA specification, all the JPA requirements regarding Serializable entities apply to Hibernate as well.
According to Tomcat documentation, the HttpSession attributes also need to be Serializable:
Whenever Apache Tomcat is shut down normally and restarted, or when an application reload is triggered, the standard Manager implementation will attempt to serialize all currently active sessions to a disk file located via the pathname attribute. All such saved sessions will then be deserialized and activated (assuming they have not expired in the mean time) when the application reload is completed.
In order to successfully restore the state of session attributes, all such attributes MUST implement the java.io.Serializable interface.
So, if the entity is stored in the HttpSession, it should implement Serializable.
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