[xwiki-devs] [Proposal] New Configuration design - xwiki-devs@xwiki.org

24 Aug 2008

Hi,

Here's a proposal for implementing configuration in the new  
architecture, using components.
Note: I think this is compatible with Sergiu's proposal here:
http://tinyurl.com/6md5jd

General requirements
=================

* Each module/component can define its own configuration
* Accessing configuration parameters from Java should be strongly  
typed (ie. getLinkLabelFormat() for getting the link label and not  
getParameter("linklabelformat"))
* It should be possible to load Configuration data from different  
sources (properties file, xml files, database, xwiki documents, etc)
* Configuration sources should have an order
* Any module/component should be able to get the configuration for  
other module/component but in read only mode
* It should be possible to dynamically add a new configuration source  
at runtime
* Configuration data should be loaded and cached

Proposed Implementation
====================

* Each module/component defines its configuration in a component which  
is a java beans. For example let's take the rendering module. We would  
have a RenderingConfiguration component as in:

public interface RenderingConfiguration
{
     String getLinkLabelFormat();
}

public class DefaultRenderingConfiguration implements Initializable,  
Reloadable, RenderingConfiguration
(in practice will extend AbstractConfiguration class probably)
{
     private String linkLabelFormat;

     // Injected
     private ConfigurationManager manager;

     public void initialize()
     {
         // Define the Configuration sources here. Default  
configuration sources would be defined in AbstractConfiguration  
probably)
         List configurationSources = ....

         // Configuration namespace (all properties should start with  
the namespace value)
         String namespace = "rendering";

         reload();
     }

     // Should be located in AbstractConfiguration
     public void addConfigurationSource(ConfigurationSource source);

     public void reload()
     {
         // Populate java bean
         manager.populate(this, configurationSources, namespace);
     }

     public void setLinkLabelFormat(String linkLabelFormat) {...}
     public String getLinkLabelFormat() {...}
}

* The DefaultRenderingConfiguration class is registered as a component  
in components.xml and with a singleton lifecycle. This means the data  
it contains are cached for the whole application lifetime. They can be  
reloaded using reload().
* The ConfigurationManager implementation will use Jakarta BeanUtils  
to automatically populate a javabeans. It'll also use Jakarta Commons  
Configuration for implementations of ConfigurationSource.
* ConfigurationSource interface should have a method like: Object  
getParameter(String name). More details to be defined later.
* Code wanting to get Rendering Configuration would simply define a  
component dependency on DefaultRenderingConfiguration and they'll have  
it injected for them.
* There'll be a XWikiDocumentConfigurationSource that gets parameter  
values from one or several xwiki documents. We'll need to define how  
we get them but we could provide some standard XWikiConfigurationClass  
for a single configuration element for example.
* The idea of the namespace is to use the package name and remove the  
"org.xwiki" or "com.xpn.xwiki" prefix. For example  
"org.xwiki.rendering.*" leads to "rendering.*".

WDYT?

If we agree I can whip up a first implementation of this relatively  
quickly I think.

Thanks
-Vincent