Re: Method invocation via proxy and reflection

From:
Piotr Kobzda <pikob@gazeta.pl>
Newsgroups:
comp.lang.java.programmer
Date:
Tue, 02 Oct 2007 00:48:23 +0200
Message-ID:
<fdrtfp$rbt$1@inews.gazeta.pl>
Stefan Ram wrote:

  I might have made some mistake. But in this case, I would
  expect an exception or an error. Instead silently the wrong
  method ?Base#dummy0()? is called. Why?


Because you are trying to cheat Java doing something which is not
normally allowed -- i.e. change private data of a Method. It succeeds
because there is no security manager active, but run it with even
default SM (-Djava.security.manager) and you'll see an exception.

The result "147" is because Java usually optimizes method invocations.
It just happened that length() is declared as first method in
CharSequence, so instead of expected invocation of length() in Delegate,
Java just invokes a first method from it.

One solution to what you are trying to achieve is already mentioned by
Daniel -- implement CharSequence by Delegate and call it directly with a
Method passed to invoke().

Another solution is to use a Map<Method, Method> (most likely HashMap)
for mappings of source CharSequence methods into Delegate methods.

Alternatively you may generate "bridge" methods using e.g. ASM, or cglib.

piotr

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