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Monday, March 13, 2017

Transient keyword vs @Transient annotation

transient is a JAVA keyword (deals with serialization) whereas @Transient is a JPA annotation (deals with persistence). 

We as software developers often tend to mix these topics, however these are two distinct features which can be leveraged as per business / technical requirements

Persistence refers to the characteristic of state that outlives the process that created it. Serialization in Java refers to the process of encoding/decoding an object's state as a byte stream.

transient keyword provides the required control over serialization process and offers the flexibility to exclude fields when the object is converted to a byte stream. Howvever JPA considers such transient fields as ones having @Transient annotation, hence the field will not be be persisted by JPA as well.

Fields annotated @Transient are converted to a byte stream when the object is serialized, However it will not be persisted by JPA.

@Transient annotation finds its use in modern world of distrubted applications where a field might be of utmost importance for distributed components but at the same time have no business value from persistence per se.

public class User implements Serializable {

 private static final long serialVersionUID = 1L;

 String firstName;
 String lastName;
 Date dateOfBirth;
 int age;


In the above example we have annotated age field as @Transient.  Age field doesnt make sense to be persisted as it must be always calculated based on dateOfBirth field.

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