Persist in DataBase with AspectJ (AOP)

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			<H1>Persisto luego existo</H1>
			<br>
			<P align="justify"><b>Sumario:</b><BR>
				One of the multiple   forms to give persistence in data base to an object of a class.
			</P>
			<P><b>Autor:</b><br>
					Mariano Lorente</P>
			<P><b>Fecha:</b><br>
					30 de Agosto 2004</P>
			<P><b>Nivel:</b><br>
					Medio
			</P>		
			<P><b>Entorno:</b><br>
				Eclipse, Java, AspectJ, JDBC, Aspect Object Programming (AOP)<br>
			</P>
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			<BR>
			<BR>
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			<ul class=download>
			<li><a href='Persist/Persist_src.zip'>Download source files -  Kb</a></li>
			<li><a href='Persist/Persist_demo.zip'>Download demo project -  Kb</a></li>
			</ul>
			<p><img src='Persist/aspecto.jpg' height='135' width='120'></p>
			<b>Indice:</b><br>
			<A href="#C1"><img src="/Images/Line.gif" border="0" width="3" height="12" />
				Introduction</A><br>
			<A href="#C2"><img src="/Images/Line.gif" border="0" width="3" height="12" />
				Aspect abstract</A><br>
			<A href="#C3"><img src="/Images/Line.gif" border="0" width="3" height="12" />
				Aspect clase Cliente</A><br>
			<A href="#C4"><img src="/Images/Line.gif" border="0" width="3" height="12" />
				Test</A><br>
			<A href="#C5"><img src="/Images/Line.gif" border="0" width="3" height="12" />
				Conclusion</A><br>
<br>
<br>

<A class="ContentTitle" name="C1">Introduction</A>
<p align="justify">
The power to in a while provide dice to an object of a class persistence, can make see the capacity us that has the 
Aspects. Since we can give this behavior to the objects of a class, that does not have it, if to have to change its 
codification.<br>
<br>
There will be people who will understand that the persistence is not an aspect of a class, since a part inherent of 
the class at issue can be considered and therefore it is not possible to be understood like an aspect, mainly when 
speech of business objects. But the certain thing is that when we spoke of ' objects of negotiated   
we say this same one and not ' objects of businesses persistentes'. As it is understood a business object contains 
the logic of the business of supports this class. Another aspect is as this information in a data base keeps to make 
it persistent.<br>
<br>
Let us consider another situciación, we suppose that we have developed several systems of persistence, one that stores 
the data in XML, another one in flat text files, another one in data base.<br>
<br>
Now we put the following example of migration.<br>
<br>
In a while dice we have developed an application in which we have a class of  Configuration   
that stores the data of configuration of the application, due to the initial use of this application we have considered 
which we are going to keep these data from configuration in a file XML, but with time this application has grown and 
now it is that the configuration data we needed them to have a network since is necessary that they share all the corporative 
applications in installed her, for it we have chosen to keep the data in data base since all the equipment will be able 
to have access to the data base. If the class were programmed with aspects  Configuration   
it would not undergo any change since the only thing that we would change would be the aspect to apply to this class.<br>
<br>
Next we are going to see the way that has been followed to give persistence to the objects of a class.
</p>
<br>
<br>

<A class="ContentTitle" name="C2">Aspect abstract</A>
<p align="justify">
In the first place first that has been developed it has been an abstract aspect called  Persistence   that goes has 
to allow to extend it with other aspects. This abstract aspect contains all the points of abstract cuts that define 
the behavior of the aspect in a while given.<br>
<br>
The declaration of the points of abstract cuts is due to sobrewrite in the aspect that extends the abstract aspect, 
capturing the execution of the tie points that wish for the execution of the point of wished cut.<br>
<br>
This abstract aspect as well extends the CapaDatos  class 
  that contains all the functionality to give persistence to an object.<br>
<br>
When extending the CapaDatos  class   we accede to the functionality 
of this class from the aspect, just as if one had declared all 
its functions within the own aspect.</p>
<br>
<pre>
<b>Figura 1.</b> Persistencia.aj

package persistencia_Aspect;

import java.sql.*;
/**
 * @author [email protected]
 */
abstract aspect Persistencia extends CapaDatos {
	
  declare parents : FormularioCliente implements ObjetosRelacion;
		
  Persistencia() {
    super();
    System.out.println("constructor Persistencia");
  }
	
  abstract pointcut quieroLeer();
  abstract pointcut quieroGrabar();
  abstract pointcut quieroBorrar();
	
  after() : quieroLeer() {
    leer();
  }
	
  before() : quieroGrabar() {
    grabar();
  }
	
  before() : quieroBorrar() {
    borrar();
  }
	
  public void FormularioCliente.addObjetoRelacion(Object obj) {
    addObjeto((Cliente)obj);
  }
}
</pre>
<p align=justify>
Lo primero que se puede apreciar en la declaración del aspecto es el siguiente código:<br>
<pre>
declare parents : FormularioCliente implements ObjetosRelacion.
</pre> 
<br>
Here this indicating itself to him that the FormularioCliente class 
(In one more a developed implementation a 
form would be a class representing bases) goes has to implement the
 ObjetosRelacion  interface.<br>
<br>
At the end of the declaration of the aspect the following code can be seen:
<pre>
public void FormularioCliente.addObjetoRelacion(Object obj) {
    addObjeto((Cliente)obj);
}
</pre>
<p align="justify">
Where the method has been implemented that contains the ObjetosRelación  interface.<br>
Not being the intention of this article treating the relations between objects, 
a basic implementation and of the 
relations between objects has been made minimum.<br>
<br>
Will be an aspect the relations of objects?<br>
<br>
Next we are going to see the most important part of the declaration of the aspect. </p>
<pre>
  abstract pointcut quieroLeer();
  abstract pointcut quieroGrabar();
  abstract pointcut quieroBorrar();
	
  after() : quieroLeer() {
    leer();
  }

  before() : quieroGrabar() {
    grabar();
  }
	
  before() : quieroBorrar() {
    borrar();
  }
</pre>
<p align="justify">
Three points of abstract cuts are declared, that will be due to sobrewrite in the aspects 
that the present one extends.<br>
As we can see this does not prevent that they are possible already to be declared 
 advice   for these points of cut.  
Within these  advice   is called to the methods contained within the CapaDatos  class
   since we have extended to him 
and for that reason we can make use of them.</p>
<br>
<br>

<A class="ContentTitle" name="C3">Aspecto Cliente</A>
<p align="justify">
One of the idea at the time of carrying out this small project, has been to have 
to write the smaller code possible to 
give persistence to the objects of a certain class. And a code similar to the
 PersistenciaCliente  aspect   will be 
the one that we will have to write to give persistence to the objects 
that we wish.</p>
<pre>
<b>Figura 2. </b> PersistenciaCliente.aj

package persistencia_Aspect;

import java.sql.*;
/**
 * @author [email protected]
 */
aspect PersistenciaCliente extends Persistencia {

  PersistenciaCliente() {
    System.out.println("constructor PersistenciaCliente");
  }
	
  pointcut quieroLeer() : execution(* *.leer_click());
  pointcut quieroGrabar() : execution(* *.grabar_click());
  pointcut quieroBorrar() : execution(* *.borrar_click());

  public String[] clave() {
    String[] a = new String[] {"IdCliente={$getId}"};
    return a;
  }
	
  public String sqlIdentityField() {
    return "{$setId}";
  }
	
  public String sqlSelect() {
    return "SELECT IdCliente{$setId}, Nombre{$setNombre}, Email{$setEmail} FROM Cliente";
  }
  
  public String sqlUpdate() {
    return "UPDATE Cliente SET Nombre='{$getNombre}', Email='{$getEmail}'";
  }
	
  public String sqlInsert() {
    return "INSERT INTO Cliente(Nombre, Email) VALUES('{$getNombre}', '{$getEmail}')";
  }
	
  public String sqlDelete() {
    return "DELETE FROM Cliente";
  }
}
</pre>
<p align="justify">
Once sight all the code that composes the PersistenciaCliente  aspect   
we are going to enter to develop the detail of 
the same one.<br>
<br>
In the following code:
</p>
<pre>
  pointcut quieroLeer() : execution(* *.leer_click());
  pointcut quieroGrabar() : execution(* *.grabar_click());
  pointcut quieroBorrar() : execution(* *.borrar_click());
</pre>
<p align="justify">
we can suspect that it is the code that on writes the points of abstract cuts
 defined in the aspect  Persistence. 
And we suspected well because he is that what does. As it indicates the first
 point of cut we want that the cut 
point is executed when the execution of the method is captured  leer_click.<br>
<br>
As we can appreciate has not declared no  advice   with which the code of the advices of the abstract aspect will 
be executed  Persistence.<br>
<br>
The rest of methods is not more than on writing of methods of the CapaDatos 
 class   since the abstract aspect  Persistence   extends 
this class and the PersistenciaCliente  aspect   extends the aspect  Persistence.<br>
<br>
Note:   the words that accompany sentence SQL and key it is not more than a 
form to indicate in that functions we want to establish the values or of which
 functions we want to recover the values. Thus we are parseando the values of the
 fields of the layer from data to the fields of the business object.<br>
<br>
Let us take as example the following sentence:<br>
<i>SELECT IdCliente{$setId}, Nombre{$setNombre}, Email{$setEmail} FROM Cliente</i><br>
<br>
In previous sentence SQL it is being indicated to him that it recovers of the data base 
 the IdCliente,  Name   and  
email   of the table  Client. What no longer {is normal is the following  code$$setId>}
, evidently this is not code 
SQL but it goes has to serve to us to make the parseo between the data of the data 
base and the functions of the 
business object Client. Thus we will establish or recover the values of the methods of 
the business object.</p>
<br>
<br>

<A class="ContentTitle" name="C4">Test</A>
<p align="justify">
Finally single it is to see the class that goes has to allow to us to make the 
opportune tests. It is necessary to 
mention the following code  formulario.addObjetoRelacion(cliente)   
since object relates them to the 
FormularioCliente  class. Account is necessary to occur that the
 FormularioCliente  class   does not contain the 
method at issue and that this provides through the abstract 
aspect Persistence  to him.</p>
<pre>
package persistencia_Aspect;
/**
 * @author [email protected]
 */
import java.lang.reflect.*;
public class Test {
  public static void main(String[] args) {
    FormularioCliente formulario=new FormularioCliente();
		
    Cliente cliente=new Cliente();
    cliente.setId(1);
    Cliente cliente2=new Cliente();
    cliente2.setId(2);
		
    formulario.addObjetoRelacion(cliente);
    formulario.addObjetoRelacion(cliente2);
    formulario.leer_click();

		
    System.out.println("nombre del 1: " + cliente.getNombre() + 
      " ruta: " + cliente.getEmail());
    System.out.println("nombre del 2: " + cliente2.getNombre() + 
      " ruta: " + cliente2.getEmail());
	
    cliente.setNombre("nombre del 1 cambiado");	
    formulario.grabar_click();	


    cliente2.setNombre("nombre del 2 cambiado");
    Cliente cliente3=new Cliente();
    cliente3.setNombre("nuevo");
    cliente3.setEmail("Nueva");
		
    formulario.addObjetoRelacion(cliente3);
    formulario.borrar_click();
  }
}
</pre>
<br>
<br>

<A class="ContentTitle" name="C5">Conclusión</A>
<p align="justify">
Evidently this is not the definitive solution to give persistence to an object of
 a class, but it approaches us one 
of the multiple forms to do it.<br>
<br>
Maybe you throw in lack the code of the CapaDatos  class, but it is provided
 in zip of the example, as well as the 
one of other classes or interfaces nonmentioned.
</p>
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