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#Java serialization data version 5 how to#
Once I showed them how to doĪutomatic serialization replacement, the transition to HashMap proceeded as planned. The team felt stuck, but only because they didn't know somethingĬrucial (and somewhat obscure) about Java Serialization: it was built toĪllow for evolution of types over time. Monumental task), it seemed that Hashtable would be the application's storage format for the remainder of its lifetime. Short of running some kind of dataĬonversion utility over each of the persisted user settings (a The disk forms of Hashtable and HashMap areĭifferent and incompatible. This was an elegant and open-ended settings system, but it fell apart when the team decided to migrate from Hashtable to HashMap from the Java Collections library. When a user changed his or her settings, the Hashtable was simply rewritten back to disk. Serialization API, including tricks (and code) for refactoring,Įncrypting, and validating serialized data.Ī year or so prior, a developer responsible for managing the application's per user settings had decided to store them in a Hashtable, then serialize the Hashtable down to disk for persistence. In this article Ted Neward gives you five reasons to look twice at the Java Object Serialization rewards those who go digging. But, like many aspects of the Java platform, Summary: Java Object Serialization is so fundamental to Java programming that It's highly recommended that you explicitly declare and initialize the static, final field of type long and named 'serialVersionUID' in all your classes you want to make Serializable instead of relying on the default computation of the value for this field even if you are not gonna use versioning.Ted Neward, Principal, Neward & Associates If that is not the case, it throws an InvalidClassException. The Serialization Runtime verifies that serialVersionUID read from the de-serialized data and the serialVersionUID declared in the class are exactly the same.
This value is used for checking the compatibility of the classes with respect to serialization and this is done while de-serializing a saved object. But, the value is not guaranteed to be the same across all compiler implementations. This computation depends upon various aspects of the class and it follows the Object Serialization Specifications given by Sun. If the class doesn't have this field declared explicitly then the compiler will create one such field and assign it with a value which comes out of a implementation dependent computation of serialVersionUID. When you implement java.io.Serializable interface to make a class serializable, the compiler looks for a static final field named serialVersionUID of type long. Visibility (controlling access to members of a class).Using ThreadPoolExecutor in MultiThreaded applications.Using Other Scripting Languages in Java.Splitting a string into fixed length parts.Custom JSON Deserialization with Jackson.Parallel programming with Fork/Join framework.Java Pitfalls - Threads and Concurrency.
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