What is the use of implementing Serializable interface in hibernate entity class?
That interface continue nothing in that.
It's Marker Interface and just like an normal interface.
The marker interface pattern is a design pattern in computer science, used with languages that provide run-time type information about objects. It provides a means to associate metadata with a class where the language does not have explicit support for such metadata.
In Serializable case java
public interface Serializable{
}
and some class
public class someObje implements Serializable{
}
And somewhere else Runtime realizes objects like
if(someObje instnaceOf Serializable){
//Hey this object can serialize you know. Grant security permission.
}
Coming to your question, by definition
Serialization where an object can be represented as a sequence of bytes that includes the object's data as well as information about the object's type and the types of data stored in the object.
Now without Serialization ,how hibernate entities move in your application (Client <=> Server <=> Database)?
And also to detect the type. For ex in hibernate look at the method signature of Seesion#get() method
Object get(Class clazz,
**Serializable** id)
throws HibernateException
Note:This theory applies not only for hibernate entities where ever Object needs to be serialize.
Not sure why in Hibernate entity classes need to implement Serializable interface. A Serializable POJO is the one which can be written to the disc or transmitted over the wire.
If your Hibernate entities or POJOs are involved in any of these then only you need to implement Serializable interface.
EDIT:
- Just realized that the keys (primary, composite) needs to be Serializable as they are referred by persistent Session. (Reference)
Related
I noticed in Spring-boot a lot of people create models/entities and implement the Serialiazable interface.
public class ModelBase implements Serializable
I understand what it means to serialize data/classes as it enables you to save the state of a class (if I'm not wrong, to a file for instance).
But I believe this should be done only when necessary, but either way it seems people just tend to implement the interface.
Is there a different reason?
When your models or entities are meant to travel across several JVM's then you might want to consider implementing Serializable interface. You should do this with caution. You should also provide a a valid UUID for the class to be used during Serialization and vice versa.
Sample is
private static final long serialVersionUID = 9178661439383356177L;
And
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.
Also
When using serializable values it is possible to remove this redundancy by changing the entity class in two ways:
Make the entity class serializable, so it can be used in place of the value class.
Make the key fields transient, so they are not redundantly stored in the record.
https://docs.oracle.com/cd/E17277_02/html/collections/tutorial/SerializableEntity.html
I am new to MyBatis, I saw some code which define model as
public class model implement serializable {
****
}
but some codes simple define without serializable interface.
I am wondering which is better? Serializable is an empty interface actually.
You need to define the Serializable interface if you plan to serialize instances of your class. It's that simple.
Many do it out of routine, but the entire point of Serializable is that some classes can NOT be serialized correctly. By making you implement this interface, you make the conscious decision that your class, in fact, can be serialized.
Mybatis don't require serialization. It dynamically calls constructor after executing query and create bean objects.
So answer is no you don't need to implement Serializable interface.
Serializable is a marker interface and has no method. It just tell jvm that you are intrested to serialize the type and rest will be done automatically.
Many times I see a model class will implement Serializable, but is never serialized.
What is purpose here to implement Serializable?
If serialization is not used, what will I miss? Is there any effect in the way the code communicates?
public class Stock implements Serializable{
private int stockId;
private String stockCode;
private String stockName;
//Getter and setter
}
What is purpose here to implement Serializable?
Just a marker to indicate the possibility provided to clients of the class for serializing instances of them if they wish.
For example, if you instantiate Stock class and that you want to save Stock instances in a file, you can do it thanks to this marker. APIs (for example Jaxb or Java native serialization mechanism) rely generally on the implementation of this interface to serialize class.
If serialization is not used, what will I miss? Is there any effect in
the way the code communicates?
It's is not used, you have zero overhead or transformation in the communication of the instance since it is a marker interface. Only, when the serialization occurs, the communication of the instance changes.
Serializable is just a marker interface without overhead*.
If you want class A to implement serializable and class A contains field with type Stock, Stock should also implement serializable.
May be there will be no direct Stock class instance serializations. But it will be serialized via class A instance.
Also implementing is necessary if you want Stock instance to become an argument of
type foo(? extends Serializable param)
If I want to map sql to some object in MyBatis, then I need to implement Serializable interface.
Like this:
public class User implements Serializable {
Otherwise it throws NotSerializableException when I try to map sql results to this object.
Is there any way to congigure MyBatis such that it allows me to have domain object not implementing Serializable?
I found the reason why mybatis needs serializable object.
Normally, when you do not use <cache /> tag, everything works fine without implementing serializable interface.
The reason is that mybatis need to read/write object via serialization.
This link may help https://mybatis.github.io/mybatis-3/sqlmap-xml.html
We don't need it if we're implementing Serializable. So why this difference? How does it relate to the actual mechanism of Serialization?
A thorough explanation (although the grammar of the article might be improved) can be found on http://www.jusfortechies.com/java/core-java/externalization.php . The short answer, for future reference in case the linked page goes away:
Externalizable is an interface extending Serializable. Contrary to Serializable, though, objects are not restored by just reading the serialized bytestream, but the public constructor is called and only once the object is thus created, its state is restored. This makes restoring more efficient.
Edit: See also What is the difference between Serializable and Externalizable in Java? .
This is primarily used for caching purposes. In order to deserialize across streams, you will need to spell out how you want your object to be deserialized, hence the two methods provided by the contract in Externalizable interface: writeExternal and readExternal. Note that Externalizable extends Serializable, so you don't necessarily need to implement Serializable interface (although it's a marker interface and there are no methods to be actually implemented).
For a sample implementation, have a look at MimeType.
A public no-arg constructor is needed while using Externalizable interface.
Because in case of Serializable
readObject reads the required information from the ObjectInputStream
Serialization uses reflection mechanism to get the necessary fields and their corresponding values.
Serializable serializes all the data members (except static and transient).
But in case of Externalizable
No reflection mechanism used.
User doesn't serializes all data members.That's why to fetch values of the members which are not externalized public no arg constructor is required.