Hello,
I am writing my masther's thesis about aop and I am about to write a definitions and
overview chapter. In that chapter I am giving an overview over existing AOP systems,
and JBoss AOP is surely a candidate I want to be in that chapter. My plans were to
create a common example and to show how and why the implementation of the example
differ.
For that reason I have a simple example, a stack class:
public class Stack
| {
| private class StackObject
| {
| private Object content;
| private StackObject next = null;
|
| public StackObject ( Object o, StackObject s )
| {
| this.content = o;
| this.next = s;
| }
|
| public StackObject getNext ()
| {
| return this.next;
| }
|
| public Object getContent ()
| {
| return this.content;
| }
| }
|
| private StackObject top = null;
| private int height = 0;
|
| public Stack () {}
|
| public synchronized Object pop ()
| {
| if ( this.top == null )
| {
| // contract violation - a real program would throw an exception
| return null;
| }
|
| -- this.height;
|
| StackObject temp = this.top;
| this.top = temp.getNext ();
|
| return temp.getContent ();
| }
|
| public synchronized void push ( Object o )
| {
| this.top = new StackObject ( o, this.top );
|
| ++ this.height;
| }
|
| public synchronized int size ()
| {
| return this.height;
| }
| }
Now I have "identified" two aspects:
* Size
* Synchronization
Contract Enforcement would be a candidate, too, but I didn't want to overcomplicate
the example. So my AspectJ implementation is (untested, but compiles):
Stripped down stack class:
public class Stack
| {
| private class StackObject
| {
| private Object content;
| private StackObject next = null;
|
| public StackObject ( Object o, StackObject s )
| {
| this.content = o;
| this.next = s;
| }
|
| public StackObject getNext ()
| {
| return this.next;
| }
|
| public Object getContent ()
| {
| return this.content;
| }
| }
|
| private StackObject top = null;
|
| public Stack () {}
|
| public Object pop ()
| {
| if ( this.top == null )
| {
| // contract violation - a real program would throw an exception
| return null;
| }
|
| Object temp = this.top.getContent ();
| this.top = this.top.getNext ();
|
| return temp;
| }
|
| public void push ( Object o )
| {
| this.top = new StackObject ( o, this.top );
| }
| }
The size aspect:
public aspect StackHeight
| {
| private int Stack.height = 0;
|
| public int Stack.size ()
| {
| return this.height;
| }
|
| after ( Stack s ) returning: target ( s ) &&
| call( public void Stack.push(..) )
| {
| ++ s.height;
| }
|
| after ( Stack s ) returning: target ( s ) &&
| call( public * Stack.pop(..) )
| {
| if ( s.height > 0 )
| {
| -- s.height;
| }
| }
| }
And the synchronization aspect:
public aspect StackSynchronization
| {
| // 1:
| private boolean Stack.semaphore = false;
|
| // 2:
| before ( Stack s ): target ( s ) &&
| call( public * Stack.*(..) ) && within( Stack )
| {
| synchronized ( s )
| {
| if ( s.semaphore == true )
| {
| try {
| s.wait ();
| } catch(InterruptedException e) {}
| }
|
| s.semaphore = true;
| }
| }
|
| // 3:
| after ( Stack s ): target ( s ) &&
| call( public * Stack.*(..) ) && within( Stack )
| {
| s.semaphore = false;
| s.notify ();
| }
| }
My problem here is that I use static introductions and I wasn't able to figure out how
this is done in JBoss AOP. I know how changes in the hierarchy and the type system are
done, but not how I can change the static structure of a class with JBoss AOP. - Is
this even impossible with JBoss AOP?
Any help appriciated.
Many thanks in advance,
Franz
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http://www.jboss.org/index.html?module=bb&op=viewtopic&p=3840580#3840580
Reply to the post :
http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&p=3840580
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