Date: 2004-01-27T18:29:33
Editor: NiclasHedhman <[EMAIL PROTECTED]>
Wiki: Apache Avalon Wiki
Page: IntroductionToEmbedding
URL: http://wiki.apache.org/avalon/IntroductionToEmbedding
no comment
Change Log:
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@@ -1,7 +1,4 @@
-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.
+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'''''
@@ -10,122 +7,73 @@
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.
+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:
+ 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
- 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).
+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).
- The contents of the meta file includes:
+The contents of the meta file includes:
- * a ordered list of jar files that are required to
- construct a classloader for the embedded application
+ * a ordered list of jar files that are required to construct a classloader for
the embedded application
- * the name of a factory class to be used as the embedded
- instance creator
+ * the name of a factory class to be used as the embedded instance creator
3. create the factory
- Using the initial context and the artifact you now have everything
- you need to create you embedded instance.
+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.
+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:
+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.
+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:
+''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.
- A we 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.
+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:
+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.
+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'''''
merlin/logging/logkit
- Package contains an example of a logging manager
- that is established as part of merlin establishment.
- Key classes include the DefaultLoggingCriteria and
- DefaultLoggingFactory - the test package demonstrates the
- complete deployment of the logging manager with nothing more
- than avalon-repository-main in the project.xml dependencies.
-
- Usage of this factory can be seen in the merlin/kernel/impl
- package - DefaultFactory class under the createLoggingManager
- operation.
+Package contains an example of a logging manager that is established as part of
merlin establishment. Key classes include the DefaultLoggingCriteria and
DefaultLoggingFactory - the test package demonstrates the complete deployment of the
logging manager with nothing more than avalon-repository-main in the project.xml
dependencies.
+
+Usage of this factory can be seen in the merlin/kernel/impl package - DefaultFactory
class under the createLoggingManager operation.
merlin/kernel/impl
- The kernel/impl package defines the factory that is used to
- create a new Merlin Kernel. Examples of embeddors that
- use this factory include:
+The kernel/impl package defines the factory that is used to create a new Merlin
Kernel. Examples of embeddors that use this factory include:
* merlin/kernel/cli - Main class
* merlin/kernel/plugin - MerlinBean
* merlin/kernel/servlet - MerlinServlet
* merlin/kernel/unit - AbstractMerlinTestCase
-Please note that there are some small differences between the 3.2 and
-3.3 versions of the APIs. The above description of based on 3.3 (CVS HEAD).
+Please note that there are some small differences between the 3.2 and 3.3 versions of
the APIs. The above description of based on 3.3 (CVS HEAD).
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