On 6/28/2016 3:56 AM, Mark Thomas wrote:
On 27/06/2016 22:35, Jerry Malcolm wrote:
Mark,
On 6/27/2016 1:07 PM, Mark Thomas wrote:
On 27/06/2016 17:44, Jerry Malcolm wrote:
I'm assuming that context.lookup(...) simply locates the "jdbc/myDB"
<Resource> tag in the context.xml file, pulls all of the parms out of
that tag, creates a DataSource object utilizing the parms, and returns
it. If that's the case, couldn't I create a variation/subclass of the
Context object that modifies the url parm that it found in the resource
tag and puts the desired db name into the url before constructing the
DataSource?
Sure.
You need to implement the appropriate factory and then specify your
factory class explicitly in the Resource element using the factory
attribute.
You probably want to start here for ideas on how to code up your factory:
http://svn.apache.org/viewvc/tomcat/trunk/java/org/apache/naming/factory/
or for a more specific example:
http://svn.apache.org/viewvc/tomcat/trunk/java/org/apache/tomcat/dbcp/dbcp2/BasicDataSourceFactory.java?view=annotate
Mark
Thanks so much. This looks doable. Just to make sure I have the big
picture correct....
1) I will define a new custom resource that returns a custom context
object that I write.
2) On the <Resource> tag for my custom context resource I can put all of
the standard DataSource parms
3) I then call lookup() on this custom context passing the dbName in
4) This custom context will build an appropriate Reference object with
all the parms, instantiate a BasicDataSourceFactory, and call
getInstance(.....) on the factory.
When I need an instance of the datasource:
Context initContext = new InitialContext();
Context envContext =
(Context)initContext.lookup("java:/comp/env");
MyDataSourceContext dsContext = (MyDataSourceContext)
envContext.lookup( "dsContext/myDSContext" );
DataSource myDS = (DataSource) dsContext.getInstance( "dbName" );
Am I getting close?
Yes, but I don't think you want to use custom NamingContexts. I think
there is a simpler way.
1. Write a custom DataSource factory that provides a getDataSource(...)
method that allows you to pass in whatever per instance config you need.
This DataSource factory will need to use bean style setters (like the
example I linked to) to pick up the other config from the <Resource .../>
2. Write a custom resource factory that returns an instance of your
DataSource factory.
3. Add a context Resource element for your DataSource factory,
remembering to use the factory element and specify the custom resource
factory from 2.
HTH,
Mark
If external configuration were not required, would there be a problem
instantiating a DataSource directly and setting any required properties
programmatically? Would any functionality be lost?
Also, if there were base properties set in a <Resource> element, would
there be a problem using a copy of the properties from that data source,
modified as necessary, to instantiate a new DataSource?
-Terence Bandoian
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