Carsten Ziegeler schrieb:
[…]
Client code inside a web application:
public void parameterizeComponents(Request req, Pipeline pipeline) {
for (Iterator i = pipeline.getComponents().iterator(); … ) {
PipelineComponent c = (PipelineComponent) i.next();
if (c instanceof WebappPipelineComponent) {
WebappPipelineComponent wpc = (…) c;
wpc.setRequest(req);
}
}
}
The pipeline is executed in a specific environment. The actual
pipeline object itself is oblivious of the environment information, but
the pipeline components are directly dependent on the environment.
>
Hmm, yes this would work, but :) this would make it harder to have a
reusable pipeline implementation that frees my application from passing
the information to the components.
Does it make a big difference if the information is passed to the
pipeline or to the components? To get rid of the boilerplate loop above,
the visitor pattern could be used:
public class Webapp implements PipelineEnvironment {
public void preparePipelineForExecution() {
// let the pipeline visit its components
this.pipeline.setEnvironment(this);
}
/**
* @see PipelineEnvironment.environmentalize(…)
*/
public void environmentalize(PipelineComponent c) {
if (c instanceof WebappPipelineComponent) {
WebappPipelineComponent wpc = (…) c;
wpc.setRequest(req);
}
}
}
Currently the app creates a map, passed it to the pipeline
implementation and this implementation passes the map on to the components.
With the approach above, I would need a custom pipeline implementation
to do this.
Hmm, why would you need a custom pipeline implementation? Wouldn't this
be generic enough:
public class PipelineImpl implements Pipeline {
public void setEnvironment(PipelineEnvironment env) {
for (Iterator i = getComponents().iterator(); … ) {
PipelineComponent c = (…) i.next();
env.environmentalize(c);
}
}
}
Furthermore there might be a lot of marker interfaces to test.
The marker interfaces wouldn't be generic, but application-specific, so
there would only be one needed per application.
I imagine to use application-specific wrappers for "standard" pipeline
components, e.g.
public class WebappXsltTransformerWrapper implements Transformer,
WebappPipelineComponent {
private XsltTransformer delegate;
public void setRequest(Request req) {
if (this.useRequestParams()) {
this.delegate.setXsltParams(req.getParameterMap());
}
}
}
In this case the application can provide a layer of classes to adapt the
standard pipeline components to the application-specific environment.
The marker interface check would allow to use other components as well -
they just wouldn't be "environmentalized".
-- Andreas
--
Andreas Hartmann, CTO
BeCompany GmbH
http://www.becompany.ch
Tel.: +41 (0) 43 818 57 01
