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From Matthijs Wensveen <...@wanadoo.nl>
Subject Re: New commons subproject vs. Configuration project
Date Tue, 15 Jul 2003 14:51:41 GMT
I am currently working on a separate site on sourceforge to place all 
files, documentation and examples, but hopefully we can place it on 
Apache some day soon.
This is how it works:
There is a singleton Context instance that is provided by a Context 
subclass. Currently there are 2 implementations, StandaloneContext and 
WebContext, and it will be easy to provide a JNDIContext.
After initializing, you reference the Context by calling 
Context.getInstance(). So your calling classes will be unaware of the 
underlying implementation.

The Context initialization consists of parsing an XML file and 
delegating XML Nodes to specific handlers.
For example, config.xml:
<?xml version="1.0"?>
<config>
    <element-handler 
class="nl.func.util.context.handlers.PropertiesHandler" 
root-element="properties" />

    <properties name="mail.settings">
        <property key="mail.host" value="mail.planet.nl" />
        <property key="default.from" value="info@func.nl" />
        <property key="default.bcc" value="m.wensveen@func.nl" />
    </properties>
</config>

Now we can initialize a StandaloneContext, for example: (WebContext is 
usually initialized in web.xml as a ContextListener)
new StandaloneContext("config.xml"); // this will initialize a singleton 
Context

Using the Context instance, you can lookup all configured objects by calling
Context ctx = Context.getInstance();
(Properties) mailSettings = ctx.lookup("mail.settings");

I'll send a link to the sourceforge project as soon as it's there.

-Matthijs.


Mark R. Diggory wrote:

> Wow, I've always wanted a JNDI SPI for XML files! I imagined one day
> using JXPath as the base for the search/getAttributes/lookup in such a
> way as to have the XML content be very open and unrestricted and the
> search filter syntax would be XPath.
>
> /* an XmlContext is a DirContext over XML files */
> javax.naming.xml.XmlContext ctx = new
> javax.naming.xml.XmlContext(Hashtable env);
>
> Element e = (Element)ctx.lookup("/foo/bar[2]");
>
> Attributes atts = ctx.getAttributes("/foo/bar");
>
> NamingEnumeration enum = ctx.search("/foo","[bar/@bam =
> 'boom']",searchControls);
>
> while(enum.hasNext()){
>    Element e = (Element)enum.next();
>    ...
> }
>
> I imagined it would also be used to write attributes, elements to create
> new "subcontexts". Imagine, a fully read/writable Configuration
> framework... :-)
>
> ctx.modifyAttributes("/foo/bar", attrs);
> ctx.createSubContext("/foo/bar", "bam");
> ctx.destroySubContext("/foo/bar/bam");
>
> I've been hoping for a way to supply a XML Configuration based
> replacement for our current JNDI based distributed config which uses
> LDAP servers.
>
> Henri's right, there is room in the commons for multiple
> implementations. I think this really promotes a path of
> development where really good alternate approaches can exist.
> Coevolution can often result in better adaptations to an environmental 
> condition.
>
> -Mark



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