Huxi LI wrote:
**Hi everyone,
I would like to launch a discussion about implementation of self-discovery
feature in Ant.
The idea is that when users drop a jar in share directory, all custiom tasks
and datatypes
should be discovered automatically by Ant. The same is true when jars are
removed
from the share directory.
The advantage is that users do not need any more use Taskdef to declare
custom
tasks. This makes Ant a highly extensible "plug-and-play" system.
Modern systems are becoming more
and more intelligent. I think Ant maybe do better. The concept of
"plug-and-play" is not
any more a vocaburary reserved for hardware components; software is also
advancing in this direction. An
extensible system should be able to "dynamically" discover available
services and have conflict detection and resolution
capability.
Which is precisely why it is in Ant1.6. You add a new JAR to the system,
all datatypes and tasks will be exported in a namespace of your choosing
via an xmlns:mytasks="antlib:org.example.package" declaration.
http://ant.apache.org/manual/index.html
We deal with conflicts and resolution by requiring antlib libraries to
be imported into separate namespaces, thus the act of declaring the
namespace not only forces the loading of the new tasks, it gives you the
separation
> A simple example of self-discovery is the "hot deployment" service
available
> in most J2EE
> application servers. The complexity of implementation such a mechanism
> depends on many factors. Sometimes it
> is not the complexity to implement self-discovery service; it is often
> simple ignored by developers. For the
> Ant build system, it is fairly easy to implement self-discovery feature.
J2EE hot deploy is a very different beast, and, if you use it a lot, you
will soon see why cold restart works better. The app servers are trying
to reload stuff in existing classloaders and it is very easy for old
state to be retained.
-Steve
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