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From bugzi...@apache.org
Subject DO NOT REPLY [Bug 16726] - External FilterReaders don't get chain()ed
Date Mon, 03 Feb 2003 18:49:19 GMT
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http://nagoya.apache.org/bugzilla/show_bug.cgi?id=16726

External FilterReaders don't get chain()ed





------- Additional Comments From umagesh@apache.org  2003-02-03 18:49 -------
Looking at this again, I don't think the patch would provide a lot of value.
Let me try to explain the way things currently work:

when using the <filterreader> syntax (as all custom filterreaders would),
it gets instantiated as an AntFilterReader.  If any nested <param> elements
were declared, these parameters would be constructed and set using the
setParameters method, assuming the custom filterreader implements 
Parameterizable.  All this is performed by performing an implicit "chain" -
when a new AntFilterReader instance is created, it is created using another
FilterReader which is present before it in the chain:

New AntFilterReader = new instance of AntFilterReader(previous FilterReader 
in chain).

The above ensures an implicit "chaining".

So, what is the deal with ChainableReader?
Those filterreaders that are provided out-of-the-box have a much more elegant
style of defining nextes elements without having to use <param>s.  Therefore, 
for these setters to be called we need a consistent mechanism to invoke the
various setters.  We also need a mechanism by which the chain can be 
programatically controlled.  Hence, there is the chain(Reader) method.  This
method is 'intended' to be used to create a new reader instance and invoke the
setters as appropriate.

So, going back to your original problem, the external filterreaders do get
chained, though by not calling the chain() method explicitly.

So, what do you do to remedy your situation?

Instead of having the chain method in VPPFilter, you may probably investigate
moving the logic to the initialize() method, if possible.

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