Hi Alexei,
Yes - it is possible to match those points with aspects
e.g if the class is called MyClass
log point 2 would be matched by "call(* MyClass.addSomeDataForServer()) &&
withincode(MyClass.dataExchange())"
log point 3 could be matched by "call(* MyClass.addMoreSecurity()) &&
withincode(MyClass.dataExchange())"
log point 4 could be matched by "set(MyClass.handshakePerformed) &&
args(true) && withincode(MyClass.dataExchange())"
log point 5 could be matched by "call(Exception.new(..)) && withincode(
MyClass.dataExchange())" (or by after() throwing advice on the dataExchange
method.
an alternative would be do something like this, which combines 2, 3 and 4:
after() returning(int k): execution(int MyClass.performHandshake()) &&
withincode(MyClass.dataExchange()) {
if (k == NEED_MORE_DATA) {
log("server responded: needs more data"); // log point 2
} else if (k == NEED_MORE_SECURITY) {
log("server responded: needs more security"); // log point 3
} else if (k == OK) {
log("handshake OK"); // log point 4
}
}
I wouldn't necessarily recommend doing a lot of this kind of logging with
aspects as it can make quite a messy aspect and the pointcuts can be quite
fragile (i.e. minor changes in the code can easily cause a pointcut to stop
matching). But it is possible. My second suggestion is a little more
robust and you may find that that advice could be applied more
generally anyway (e.g. 2, 3 and 4 could be logged after all calls to
performHandshake instead of just calls from MyClass.dataExchange).
Hope this helps. I'm happy to answer any further questions or take a look
at any aspects you decide to write.
Regards,
Sian
On 15/11/06, Alexei Zakharov <[EMAIL PROTECTED]> wrote:
> I'm not entirely sure what you mean by application-level logging.
Well, I mean the situation when log calls are scattered around the
code. Something like this:
---
void dataExchange() throws Exception {
boolean handshakePerformed = false;
log("in performConnection"); // log point 1
...
for (int i = 0; i < 5; i++) {
int k = performHandshake();
if (k == NEED_MORE_DATA) {
log("server responded: needs more data"); // log point 2
addSomeDataForServer();
} else if (k == NEED_MORE_SECURITY) {
log("server responded: needs more security"); // log point 3
addMoreSecurity();
} else if (k == OK) {
handshakePerformed = true;
log("handshake OK"); // log point 4
break;
}
}
if (!handshakePerformed) {
log("give up: unable to handshake"); // log point 5
throw new Exception("unable to handshake");
}
log("ready to send data"); // log point 6
....
log("leaving performConnection"); // log point 7
}
---
From your explanation I've understood that aspects can be used for
points one and seven. Is it possible to cover other log points with
aspects? What should be done for this (if so)?
Thanks,
2006/11/14, Sian January <[EMAIL PROTECTED]>:
> Hi Alexei,
>
> I'm not entirely sure what you mean by application-level logging. It is
> possible to get more fine-grained information using aspects if that's
what
> you mean, such as tracing individual methods, logging field reads and
> writes, logging when Exceptions are caught and logging when certain
methods
> are called and where from. You can't use aspects to add logging into
the
> middle of a method, unless it's at a well defined point. If there was
some
> specific information you wanted to add at a specific place there's no
> problem using a combination of aspects and hand-coded logging. Does
that
> answer your question at all?
>
> Thanks,
>
> Sian
>
>
> On 14/11/06, Alexei Zakharov <[EMAIL PROTECTED]> wrote:
> >
> > Sian,
> >
> > Cool! Thanks for this. Can AspectJ be used for something more
> > sophisticated than just tracing? For application-level logging for
> > example?
> >
> > Thanks,
> >
> > 2006/11/14, Sian January <[EMAIL PROTECTED]>:
> > > Hello,
> > >
> > > Following a recent discussion on this list I have been looking into
how
> > > aspects could be used for tracing in the Harmony class library
code. I
> > have
> > > been using AspectJ and have written a really simple tracing aspect
for
> > the
> > > math module, adapted the build.xml script and written some
instructions
> > on
> > > how to apply it. At the moment the aspect just does entry and exit
> > tracing
> > > and prints to System.out, but this is because it's a first draft -
it is
> > > possible to do more targeted tracing and to use frameworks such as
> > > java.util.logging with aspects.
> > >
> > > Steps to follow:
> > >
> > >
> > > 1. Download AspectJ from
> > > http://www.eclipse.org/aspectj/downloads.php
> > >
> > > 2. Copy aspectjrt.jar to /depends/jars/aspectj/
> > >
> > > 3. Copy aspectjtools.jar and aspectjrt.jar to ANT_HOME/lib and if
using
> > > Eclipse add both of these to your ant runtime configuration (Window
>
> > > Preferences > Ant > Runtime > Add...)
> > >
> > > 4. Edit build file to use iajc* instead of javac and include aspect
> > class
> > > files (or apply the buildxmlpatch.txt to build.xml in the math
module)
> > >
> > > 5. Write a tracing aspect (or copy the one attached to
> > > modules\math\src\main\java\org\apache\harmony\tracing)
> > >
> > > 6. Re-build the module
> > >
> > > 7. Make sure to add aspectjrt.jar to the runtime classpath of
whatever
> > > program you are running.
> > >
> > >
> > > * - iajc isn't incremental like javac in ant, it will always do a
total
> > > rebuild. Also if you switch from using iajc back to javac you will
need
> > to
> > > do a clean before you do a rebuild.
> > > Please also note that it's not possible to use this kind of tracing
for
> > any
> > > classes that are depended on by the AspectJ runtime or there will be
> > errors
> > > initializing the classes because of circular dependencies. However
I
> > think
> > > most modules apart from luni should be safe. Also it's important to
not
> > > trace methods that are called (directly or indirectly) by your
tracing
> > > methods otherwise you will end up in an endless loop.
> > >
> > > If anyone thinks this information might be useful to have available
> > > somewhere I would be happy to expand it a bit for a web page or a
Wiki
> > page.
--
Alexei Zakharov,
Intel Enterprise Solutions Software Division
--
Sian January
IBM Java Technology Centre, UK
