RE: [aspectj-users] around advice for constructor pointcut

["Ron Bodkin" <rbodkin@xxxxxxxxxxxxxx>]

Nilesh,

It sounds like you are looking for a way to do caching (i.e., return an
existing object and not create a new one). For that, you can use AspectJ's
polymorphic Object return in around advice. E.g.,

aspect Cache {
    pointcut constructingTypeInFoo() : call(com.foo..*.new(..)) 
    Object around() : constructingTypeInFoo() {
         Object cached = getCache(thisJoinPoint.getSignature(),
thisJoinPoint.getArgs());
         if (cached == null) {
             cached = proceed();
             putCache(thisJoinPoint.getSignature(), thisJoinPoint.getArgs(),
cached);
         }
         return cached;
     }

     Object getCache(Object key1, Object key2) { /* use map with
concatenated key */ }
     void putCache(Object key1, Object key2, Object value) { /* use map with
concatenated key */ }
     Map map = new ConcurrentHashMap();
}

Note that advising AspectJ's constructor call like this will allocate a
garbage object that won't be constructed if there's a cache hit (which will
be eligible for GC). See also Adrian's blog entries for more caching with
aspects:
http://www.aspectprogrammer.org/blogs/adrian/2004/06/implementing_ca.html
and
http://www.aspectprogrammer.org/blogs/adrian/2004/06/implementing_ca_1.html 

If I misunderstood and you are trying to enforce not creating objects as a
policy, you could use:

import pkg.BadType;

aspect Policy {
    declare error: execution(BadType.new(..)): "don't construct a bad type
EVER";
}

or
aspect Policy {
    declare error: call(BadType+.new(..)) && within(foo..*):
        "don't construct a bad type or any subtype from within foo or any
subpackage";
}

or even
aspect Policy {
    before() : execution(new(..)) && this(BadType) {
        throw new IllegalStateException("Should never be constructing a bad
type");
    }
}

-----Original Message-----
From: aspectj-users-bounces@xxxxxxxxxxx
[mailto:aspectj-users-bounces@xxxxxxxxxxx] On Behalf Of Nilesh Jain
Sent: Tuesday, January 17, 2006 9:43 PM
To: aspectj-users@xxxxxxxxxxx
Subject: [aspectj-users] around advice for constructor pointcut

Hi ,
I need to prevent creation of an object using aspect. For this I have  
declared a pointcut with constructor signature. But I cannot use that  
pointcut with around advice because around advice need us to specify  
a return type. Please help me out this. Is there another way to  
prevent construction of an object?
Thanks.
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