New Baby And A Six Year Old

PropertyChangeSupport - calling using AspectJ

Inspired by a post Chris (aka Kolszew) entitled JavaBeans - bad idea pl.comp.lang.java decided to prepare an example demonstrating the use of Aspect Oriented Programming (specifically AspectJ) to solve the problem presented by Chris. I'm interested in getting
setter selected classes of behavior is identical with the following words:

 
 void setText (String txt) {String oldValue = 
 this.text; 
 this.text = txt; 
 propertyChangeSupport.firePropertyChange ("text", oldValue, txt );} 
 
 

without adding in any setterze first and third of these lines of code.

The first step is to create the project. Plugin AJDT (AspectJ Development Tools ) to the Eclipse AspectJ project allows the creation of (New-> Project AspectJ) containing immediately hooked bilbioteki AJ.

I create a base class for classes of model that provides a method firePropertyChange which simply delegates the call to a private field of type PropertyChangeSupport.

 
 import java.beans.PropertyChangeSupport; 
 
 BaseModelObject {public class 
 
 private PropertyChangeSupport propertyChangeSupport = new PropertyChangeSupport (
 this); 
 
 public void firePropertyChange (final String propertyName, Object oldValue 
 final, final Object newValue) {
 propertyChangeSupport.firePropertyChange (propertyName, oldValue, newValue 
); 
 
 
}} 
 

Let's test a class that inherits from BaseModelObject:

 
 pl.kadamczyk.ajpropertychange.model package; 
 
 public class extends SomeModelObject BaseModelObject {private String 
 
 someStringProperty; 
 private int someIntProperty; 
 
 getSomeStringProperty public String () {return 
 someStringProperty; 
} 
 
 public void setSomeStringProperty (final String someStringProperty) {
 this.someStringProperty = someStringProperty; 
} public int 
 
 getSomeIntProperty () {return 
 someIntProperty; 
} public void 
 
 setSomeIntProperty (final int someIntProperty) {
 this.someIntProperty = someIntProperty; 
 
}} 
 

It is the coolest moment: create aspect of who is responsible for invoking the method firePropertyChange class BaseModelObject:

 
 pl.kadamczyk.ajpropertychange.aspects package; 
 
 pl.kadamczyk.ajpropertychange.model import. BaseModelObject; 
 
 public aspect PropertyChangeAspect {
 
 
 / ** 
 * We define "place" where applied shall Tip 
 * / 
 pointcut callSetter (Object target, Object param): target (target) & & args (arg) & & 
 execution ( void set pl.kadamczyk.ajpropertychange.model .*. *(..)); 
 
 / ** * Tip type 
   around - to execute code before and after appropriate 
 * method is called. 
 
 * * / 
 Object around (Object target, Object newval): callSetter (target, newval) {String 
 jointPoint = ThisJoinPoint.getSignature (). GetName (); 
 / / Specify the name of the field induced by the name of the setter 
 String fieldName = jointPoint.replaceFirst ("set", ""); 
 fieldName = Character.toLowerCase (fieldName.charAt (0 )) + 
 fieldName.substring (1); 
 
 try {Class clazz = 
 target.getClass (); 
 / / grab the box before the scheduled class called 
 java.lang.reflect.Field field = clazz.getDeclaredField (fieldName ); 
 field.setAccessible (true); 
 
 / / grab the old value Object oldValue 
 field field.get = (target); 
 / / allow to call setter 
 Object result = proceed (target, newval); 
 triggerPropertyChange (target, newval, oldValue, fieldName); 
 return result; 
} catch (NoSuchFieldException e) {throw new RuntimeException 
 (e); 
} catch (IllegalArgumentException e) {throw new RuntimeException 
 (e); 
} catch (IllegalAccessException e) {throw new RuntimeException 
 (e);} 
 
 
 
} / ** * Checks 
 whether the method was performed on object class that inherits from the BaseModelObject 
 *, and if so, calls on him firePropertyChange 
 * / private void 
 triggerPropertyChange (final Object target, Object newval 
 final, final Object oldValue, final String fieldName) {
 System.out.println ("Changing the value of field" + fieldName); 
 if (target instanceof BaseModelObject) 
 {/ / call the method from the base class 
 ((BaseModelObject) target). firePropertyChange (fieldName, oldValue, 
 newval); 
 
}}} 
 
 
 

Defined call pointcut specifies all methods in all classes in package pl.kadamczyk.ajpropertychange.model name that begins with "set" and the return type "void". Defining

Tips (advice) of the type around allows you to perform operations both before and after the proper method to liberate calling proceed () .

also deserves a special variable used thisJoinPoint - this is an analogy to the standard Javowego this - this variable may be used only in the context of counseling (advice). It contains many przydatnich information about the current Join Point, which is in our case caused by a particular setter. In particular, calling:

 thisJoinPoint.getSignature (). GetName () returns the name of the currently 

method invoked by the set *.

To see the result of the above aspect run a simple class with a method main () :

 
 pl.kadamczyk.ajpropertychange.launcher package; 
 
 import pl.kadamczyk.ajpropertychange.model.SomeModelObject; 
 
 public class Launcher {public static 
 
 void main (final String [] args) {
 SomeModelObject SomeModelObject mo = new (); 
 mo.setSomeIntProperty (23); 
 mo.setSomeStringProperty ('ala has a cat ");} 
 
 
} 
 

to get the console output:

Change the value of field someIntProperty
Change the value of field someStringProperty

We note at the end - This code will not work with the appropriate manager fired security, because it will not allow the method call setAccesible (true) on the fields.
Taking this into account in a different way to get the value of the field - here I used a 'hack' with the method setAccesible because it was the fastest;)