Date: 2004-04-03T05:26:54
Editor: 203.121.47.163 <>
Wiki: Apache Avalon Wiki
Page: IntroductionToEmbedding
URL: http://wiki.apache.org/avalon/IntroductionToEmbedding
no comment
Change Log:
------------------------------------------------------------------------------
@@ -1,22 +1,22 @@
This is a little introduction to embedding Merlin. The descriptions starts off with
an overview of the Avalon Repository bootstrapping system - which at the end of the
day is the core embedding technology used within the merlin platform.
-'''''Simple Embedding Example'''''
+=== Simple Embedding Example ===
1. creating an initial context
-
+{{{
File cache = new File( "my-cache" );
InitialContext context = new DefaultInitialContext( cache );
-
+}}}
The above code defines a cache directory for the repository system to use when
loading resources needed in your embedded application - and provides the directory as
an argument when creating a new InitialContext object. The InitialContext is you hook
into the repository system and the embedding machinery.
2. declare what you want to embed
-
+{{{
String spec = "artifact:avalon-logging/avalon-logkit?version=1.0-SNAPSHOT"
Artifact artifact = Artifact.createArtifact( spec );
-
+}}}
An artifact is a logical reference to a jar file (or other type of resource) that the
repository can access. The avalon-repository system uses artifact references as the
key to locating meta data about embedded classloaders. The classloader meta data is
maintained as a properties file with the .meta extension. For example the above
artifact meta address translates to:
- [host]/avalon-logging/jars/avalon-logkit-impl-1.0-SNAPSHOT.jar.meta
+{{{ [host]/avalon-logging/jars/avalon-logkit-impl-1.0-SNAPSHOT.jar.meta }}}
The content of the meta file is automatically generated using the avalon-plugin
avalon:artifact goal. Two real examples are attached (the logkit factory and the
merlin factory meta).
@@ -29,37 +29,37 @@
3. create the factory
Using the initial context and the artifact you now have everything you need to create
you embedded instance.
-
+{{{
Builder builder = m_context.newBuilder( artifact );
Factory factory = builder.getFactory();
-
+}}}
Behind the scenes the avalon-repository system has gone off, pulled down the meta
data, downloaded and cached all of the classloader entries, constructed a new
classloader, and instantiated the factory.
4. parameterizing the factory
The factory object is the central entry point of the embedded application - it is
responsible for instantiation of the embedded instance based on a supplied criteria.
The initial criteria (the defaults) are established by the factory in response to the
following operation:
-
+{{{
Map criteria = factory.createDefaultCriteria();
-
+}}}
Based on the documentation about the facility your embedding you can update the
criteria using application specific keys. All of the Merlin related criteria instances
use the avalon-util Criteria as the map implementation. This provides support for key
and type validation under the put operations and type coercion on get operations.
''For example:''
-
+{{{
String key = "avalon.logging.configuration";
File file = new File( "logging.xml" );
criteria.put( key, file );
-
+}}}
Parameterization of the criteria is typically different for each embedding scenario.
A CLI handler will for example adapt to the command line operations and set criteria
values accordingly. An application may set the criteria based on parameters declared
in a web.xml file. Typically the embedding class acts as the adapter between the
embedded context and the factory.
4. embedded instance creation
Creation of the embedded instance is now a simple one line operation:
-
+{{{
Object object = factory.create( criteria );
-
+}}}
The object that is created is the embedded application. In this example its a
logging manager that uses the logkit implementation. However, it could have been the
Merlin kernel. The only difference between the Merlin scenario and the logging
manager scenario is the initial artifact and the actions taken to parameterize the
criteria.
-'''''Examples of Embedding'''''
+=== Examples of Embedding ===
merlin/logging/logkit
---------------------------------------------------------------------
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
