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Why does JPA require a no-arg constructor for domain objects? I am using eclipselink and just got this exception during deployment.
Exception [EclipseLink-63] (Eclipse Persistence Services-1.1.0.r3639-SNAPSHOT):
org.eclipse.persistence.exceptions.DescriptorException
Exception Description: The instance creation method
[com.me.model.UserVO.<Default Constructor>], with no parameters,
does not exist, or is not accessible.
Internal Exception: java.lang.NoSuchMethodException:
com.me.model.UserVO.<init>()
Descriptor: RelationalDescriptor(com.me.model.UserVO -->
[DatabaseTable(user)])
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The arguments of a constructor can only be found by type, not by name, so there is no way for the framework to reliably match properties to constructor args. Therefore, they require a no-arg constructor to create the object, then can use the setter methods to initialise the data.
So if you won't have no-args constructor in entity beans, hibernate will fail to instantiate it and you will get `HibernateException`.
1. No-argument constructor: A constructor that has no parameter is known as the default constructor. If we don't define a constructor in a class, then the compiler creates a default constructor(with no arguments) for the class.
The JPA Specification provides its own set of restrictions, here are the two most important to us: 1. The entity class must have a no-arg constructor. The entity class may have other constructors as well.
Because it often happens that the JPA provider has to instantiate your domain object dynamically. It cannot do so, unless there is a no-arg constructor - it can't guess what the arguments should be.
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Also notice that this is not provider dependent. It is a JPA specification.
JPA v2.0 JSR-317 and v2.1 JSR-338 says:
The entity class must have a no-arg constructor. The entity class may have other constructors as well. The no-arg constructor must be public or protected.
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