You are viewing a plain text version of this content. The canonical link for it is here.
Posted to dev@ant.apache.org by do...@apache.org on 2002/03/02 01:55:31 UTC
cvs commit: jakarta-ant/proposal/myrmidon/src/xdocs classloader.xml
donaldp 02/03/01 16:55:31
Added: proposal/myrmidon/src/xdocs classloader.xml
Log:
Start to document the Containers ClassLoader
hierarchy. Adapted terminology from Catalina
as that terminology is more widely used.
Punt on antlib ClassLoader structure as that
is defined via library specific mechanisms
Revision Changes Path
1.1 jakarta-ant/proposal/myrmidon/src/xdocs/classloader.xml
Index: classloader.xml
===================================================================
<?xml version="1.0"?>
<document>
<properties>
<title>On ClassLoaders in Ant2</title>
<author email="peter@apache.org">Peter Donald</author>
</properties>
<body>
<section name="ClassLoader Management">
<p>In many ways Ant2 needs to follow rules similar to a number of
different application servers with respect to ClassLoader management.
Ant2 will create a number of different ClassLoaders that have access
to different sets of resources (and thus Classes). The main reason
for this arrangment is to partition different sections of the
application such as the Container, the Task API, task/type libraries
and support libraries.</p>
<p>The recomended structure for ClassLoader relationships is a hierarchy.
When a ClassLoader is asked for a resource (or a class) it first delegates
to it's parent to ask for the resource. If the resource is not present in
its parent ClassLoader then the ClassLoader attempts to locate the resource
in it's own store. In practice this means that all the classes (and static
variables defined by said classes) in a parent ClassLoader are shared with
the child ClassLoaders.</p>
<p>Using kooky ascii art, the specific ClassLoader structure for Ant2 is as
follows:</p>
<source>
Bootstrap
|
System
|
Common
/ \
Container Shared
/ \
Antlib1 Antlib2 ...
</source>
<ul>
<li>
The <strong>Bootstrap</strong> ClassLoader contains the classes and resources
provided by the Java runtime.
</li>
<li>
The <strong>System</strong> ClassLoader contains the classes that were made accessible
via the CLASSPATH environment variable. If the standard ant script was used then this
should only contain the classes that are used to bootstrap the ant runtime. ie
<code>$ANT_HOME/bin/ant-launcher.jar</code>
</li>
<li>
The <strong>Common</strong> ClassLoader contains the classes and resources
that are made visible to both the Container and to all the ant type librarys. This
contains all the classes that the Container uses to communicate with tasks and other
supporting infrastructure. In particular it contains the following APIs;
<ul>
<li>
<em>Task API</em> - Contains the classes that are part of the API used
to define tasks.
</li>
<li>
<em>ProjectListener API</em> - Contains the classes necessary to define new
ProjectListeners.
</li>
<li>
<em>Aspect API</em> - Contains the classes that are used to define Aspects
of the container.
</li>
<li>
<em>Container API</em> - Contains the interfaces that are required to communicate
with the objects deep within the container. <strong>NOTE</strong>: These interfaces
are not to be used by user tasks but are made available so that certain tasks (such
as <antcall/>) can be implemented. However they are subject to change without
notice between between different ant2 versions.
</li>
</ul>
<p>
These classes are loaded from all the jars present in the <code>$ANT_HOME/lib</code>
directory.
</p>
</li>
<li>
The <strong>Container</strong> ClassLoader contains all the classes and resources
that are part of the actual implementation of the Container. These classes are not
directly accessible to any Ant library or task. Some of the classes are indirectly
accessible to tasks and other elements defined in the ant librarys as they implement
interfaces defined in the <strong>Common</strong> ClassLoader. The classes that are
stored in jars in the <code>$ANT_HOME/bin/lib/</code> directory.
</li>
<li>
The <strong>Shared</strong> ClassLoader contains all the classes and resources
that are shared across all of the ant librarys (unless they are als needed by the
container in which case they should be placed int the <strong>Container</strong>
ClassLoader). This ClassLoader is populated by all the jars that are contained in
the <code>$ANT_HOME/shared/</code> directory.
</li>
<li>
The <strong>AntLib</strong> ClassLoaders each contain the classes and resources
that required by that particular library. Note that in some cases a single Ant
Library will manifest as a single ClassLoader containing a single jar. However
in some cases it is possible for one Ant Library to have multiple jars in its
ClassLoader or even have multiple ClassLoaders. See XXXX for further details.
</li>
</ul>
</section>
</body>
</document>
--
To unsubscribe, e-mail: <ma...@jakarta.apache.org>
For additional commands, e-mail: <ma...@jakarta.apache.org>