Why Java Beans have to be serializable?

Is it necessary 开发者_运维知识库that a Java Bean implements the Serializable interface?

It's one of the "typical" features as described in the Javabeans specification.

Here's an extract of chapter 2.1 What is a bean?

Individual Java Beans will vary in the functionality they support, but the typical unifying features that distinguish a Java Bean are:

• Support for “introspection” so that a builder tool can analyze how a bean works
• Support for “customization” so that when using an application builder a user can customize the appearance and behaviour of a bean.
• Support for “events” as a simple communication metaphor than can be used to connect up beans.
• Support for “properties”, both for customization and for programmatic use.
• Support for persistence, so that a bean can be customized in an application builder and then have its customized state saved away and reloaded later.

And here's an extract of chapter 5.5 Summary of Persistence:

All beans must support either Serialization or Externalization.

In practice, it's not explicitly necessary for it to function. It will in general also just work fine without implementing Serializable. It's however useful whenever you'd like to store them "plain" on harddisk or send "plain" over network. For example when it's a session scoped bean which is to be stored in the HTTP session and the server is been confugured to persist and revive HTTP sessions during shutdown/restart. At any way, whenever you face a NotSerializableException with the bean's full qualified classname in the message, then it's enough sign to let it implement Serializable.

Yes.

By definition - a Java bean is exactly that, a serializable POJO (plain old Java object), with a no-argument constructor and private fields with getters/setters.