Wood Swing Sets Blueprints

EJB3 - JPA

One of the new EJB specification is the third version of interceptors through which you can easily use the built system of aspect-oriented programming paradigm.
in EJB3 interceptors can refer both to the life cycle of beans and their business methods. Implements to be in the form of methods. Methods-interceptors could be placed in classes of grains as well as base classes of these grains, but also can be placed in separate classes (class interceptors). Methods-interceptors can have any level of access (public , package, protected, private ), But may not be for it or static nor final .
It is worth noting that the implementation interceptor is no more limited, because they can cause JNDI, JMS, other beans, JDBC, and EntityManager'a.

first InvocationContext

method-interceptor to operate effectively must be the primary context for the call, ie, an instance of the grain, information about the called business method and its parameters, and call the result. These data can be obtained by the object InvocationContext , which is passed as a parameter to the method-interceptor.
deserves special attention InvocationContext.proceed method () . Her call to go to the next interceptor control, or (if it is called in the last interceptorze in the chain) to the grain business method (if it is business interceptor methods).

second Class interceptors interceptors

class is a simple class (do not even need to be marked with specific reference), which simply has to define a method-interceptors. These classes must have a public constructor bezargumentowy.
lifecycle interceptors is closely connected with the life cycle grain to which it is assigned.
Class interceptors can be assigned to the whole grain or beans business methods through individual endorsement @ Interceptors , which takes as argument a list of interceptor classes.
In practice, joining the class interceptor looks something like this: @ Stateless

 @ Interceptors (pl.dwalczak.Interceptor1.class) public class Seed {... @ Interceptors (pl.dwalczak.Interceptor2.class) public void metodaBiznesowa () {}} 

third Lifecycle interceptors

grains to the interceptor method has been life-cycle grains should be determined one of the following statements, according to the desired stage of life: - @ PostConstruct - @ PostActivate - @ PreDestroy - @ PrePassivate If the method is defined in the class of grain, it should have the following signature: void

 \u0026lt;METHOD> () 

other hand, if there is a class interceptors it should look like tat:

 void \u0026lt;METHOD> (InvocationContext) 

4th Interceptors

business methods to the method was the interceptor for business methods, it should mark the annotation @ AroundInvoke .
In one class interceptor, beans, grains or base class that can be annotated to mark only one method, but this does not lead to a reduction to a business method of grain was only one interceptor. All interceptors defined in parent classes, interceptorach connected through the @ Interceptors annotation and that defined in the class of grain will be effect, and the sequence of their implementation will comply with the order of their declarations and the class inheritance hierarchy of the grain.
methods annotated @ AroundInvoke are performed on the call stack at samycm business method. This method should return the value returned by the method of business, and be able to throw an exception thrown by the method of business. For this reason, should have the following signature: Object

 \u0026lt;METHOD> (InvocationContext) throws Exception Interceptor 

to pass control further, ie to the next interceptor, or business methods, you should call the proceed on an object InvocationContext .

5th Support Resources

EJB3 specification
The Interceptor Pattern

What Is The Difference Of Pneumonia

interceptors - the relationship one-to-one

In this article we'll look closer to a one-to-one and mapping it in the JPA.
can say that the one-to-one relationship is a special case jeden-do-wielu/wiele-do-jednego discussed by me in the article JPA - the relationship one-to-many and many-to-one . People who are not familiar with the mapping of that relationship, I would encourage you first read that article.
A one-to-one is also in some way connected with the concept of inline objects discussed in the article I JPA - Embedded objects (components) . Well, these embedded objects are interchangeable with a one-to-one to improve performance.

first Example - a problem area

example in this article are largely taken from the JPA - Embedded objects (components) .
And here's the object model:
is a system of two classes of User and Address, where User aggregates completely Address . It is worth noting that this type of bond, in which the existence of one entity is completely dependent on the existence of another being, is very common in relationships one-to-one. Like the relationship jeden-do-wielu/wiele-do-jednego we can distinguish the parent entity ( User ) and being a child (Address ). As for one being the parent entity is only one child, in order to achieve better performance (at the expense of standardization) are often used instead of the overt embedded objects of a one-to-one. In the relational world
sample model will be presented as follows:
This model shows that the implementation of a one-to-one on the side of the database is very similar to the implementation jeden-do-wielu/wiele-do-jednego relationship, but more on that a bit later.

second Bidirectional one-to-one bidirectional relationship

is one in which both objects are mutually aware that they are in a relationship from one object, you can navigate / move to the second. However, before proceeding to discuss the mapping of this relationship, first I would write a few sentences about the database implementation.
Well, the database implements is a one-to-one by adding a foreign key to one of the two entities. It is thus quite similar to the implementation jeden-do-wielu/wiele-do-jednego relationship, in which the subordinate entity has a foreign key to the parent entity. With the difference that in this case there is no requirement that the subordinate entity owned bonds and may also be the parent entity. At the same time that there was indeed a one-to-one, and could not degenerate into jeden-do-wielu/wiele-do-jednego relationship, it must be assumed Uniqe constraint'a the foreign key column.
when you map one-to-one fundamental role annotation @ OneToOne to be determined field-binding sites are in this relationship. Interestingly, the available attributes for this endorsement is the sum of the attributes available for the annotation @ OneToMany and @ ManyToOne , which highlights the similarity of a one-to-one relationship to jeden-do-wielu/wiele-do-jednego and simultaneously enhances the high symmetry bonds in the relationship.
Optionally, you can use @ JoinColumn annotation , which will serve the foreign key specification - the column name and the definition of unique constraintu on this column. Acc. JPA specification defaults column Foreign key to nazywałaby [nazwa_drugiej_tabeli] _ [nazwa_klucza_głównego_drugiej_tabeli] and that was not founded unique constraint when generating the database schema.
fragment mapping class User :

 @ Entity @ Table (name = "user") public class User {@ OneToOne (cascade = CascadeType.ALL, optional = false) @ JoinColumn (name = "addr_id", unique = true ) private Address address; ... } 

fragment mapping class Address:

 @ Entity @ Table (name = "address") public class Address {@ OneToOne (mappedBy = "address") private User user; ... Semantics} 

annotation attributes @ OneToOne is the same as for those annotations @ OneToMany and @ ManyToOne . I refrain from discussing them again because it is already done in the article JPA - the relationship one-to-many and many-to-one .
worth noting that these mappings are correct, assuming that the owner is an entity relationship User . However, a slightly different look to the owner if the relationship was Entity Address . First of all annotation @ JoinColumn znaczyłaby to check Address.user not User.address . A similar conversion would meet the attribute @OneToOne.mappedBy .

third Unidirectional one-to-one Unidirectional relationship

is one in which only one object is aware of being in a relationship with another object, and only from him, you can navigate / move to the second object. Database programming
unidirectional one-to-one and its mapping is in part the same as in the case of two-way relationship. With the difference that we define the mapping for only one of two entities, which must be the owner of bonds - have a foreign key to another entity. What is interesting in one way relationship, as an alternative to annotation @ OneToOne can use the @ ManyToOne - as someone so much likes to obfuscate the model;) True @ ManyToOne is not possible to determine the attribute mappedBy , but in the case of one-way relationship and the use of this attribute so it would be impossible.

4th Support Resources

JPA specification
JPA - the relationship one-to-many and many-to-one
JPA - Embedded objects (components)