The Spring framework - Making Java Groovy - page 240

The @Aspect annotation tells Spring this is an aspect. The @Before annotation defines
the pointcut using AspectJ pointcut language. [ 11 ] This particular pointcut applies at all
methods that begin with the letters set that take a single argument and return void .
The trackChange method is the advice. The JoinPoint argument is supplied by
Spring when the aspect is called. It provides context for the execution. In this case, the
JoinPoint has methods to retrieve the signature of the method being advised, as well as
the arguments supplied to the method and the target object.
11 The documentation for AspectJ is hosted with Eclipse, of all places. See http://www.eclipse.org/aspectj/ for de-
tails.
To demonstrate this aspect in action, I need to configure Spring to apply the aspect, and I
need an object to advise. The latter is easy enough. The next listing shows a simple class
with three properties.
Listing 7.15. A simple POJO with three set methods
package mjg;
public class POJO {
private String one;
private int two;
private double three;
public String getOne() { return one; }
public void setOne(String one) { this .one = one; }
public int getTwo() { return two; }
public void setTwo( int two) { this .two = two; }
public double getThree() { return three; }
public void setThree( double three) { this .three = three; }
@Override
public String toString() {
return "POJO [one=" + one + ", two=" + two +
", three=" + three + "]";
}
}
The class is called POJO , and it has three properties, called one , two , and three . Each
has a getter and a setter. The aspect will run before each of the set methods.