Hi all,
some thoughts about the plugin package:
Currently the method Extension.getExtensionInstance returns a new
instance of an extension each time it is called. If an extension is a
singleton, each extension has to implement the singleton pattern.
My suggestion:
Add an instance cache to the Extension class. If an extension is marked
as a singleton, getExtensionInstance would always return the same instance.
Whether an extension is a singleton or not is determined by the
plugin.xml, for example:
<implementation id="org.apache.nutch.protocol.httpclient.Http"
class="org.apache.nutch.protocol.httpclient.Http"
singleton="true"
protocolName="https"/>
To be compatible with the current implementation, the singleton
attribute would not be required and the default value is false.
Main advantages I see:
- singleton code in extensions would disappear, the code is getting more
readable and smaller
-- static variable access would disappear (think of concurrency and
classloader issues)
- Instance control is handed over to the plugin "container"
- it's possible to have two instances of a singleton for testing purposes
What do you think?
Thomas
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