Flexible URL normalization
--------------------------
Key: NUTCH-365
URL: http://issues.apache.org/jira/browse/NUTCH-365
Project: Nutch
Issue Type: Improvement
Affects Versions: 0.9.0
Reporter: Andrzej Bialecki
Fix For: 0.9.0
This patch is a heavily restructured version of the patch in NUTCH-253, so much
that I decided to create a separate issue. It changes the URL normalization
from a selectable single class to a flexible and context-aware chain of
normalization filters.
Highlights:
* rename all *UrlNormalizer* to *URLNormalizer* for consistency.
* use a "chained filter" pattern for running several normalizers in sequence
* the order in which normalizers are executed is defined by
"urlnormalizer.order" property, which lists space-separated implementation
classes. If there are more normalizers active than explicitly named on this
list, they will be run in random order after the ones specified on the list are
executed.
* define a set of contexts (or scopes) in which normalizers may be called. Each
scope can have its own list of normalizers (via
"urlnormalizer.scope.<scope_name>" property) and its own order (via
"urlnormalizer.order.<scope_name>" property). If any of these properties are
missing, default settings are used.
* each normalizer may further select among many configurations, depending on
the context in which it is called, using a modified API:
URLNormalizer.normalize(String url, String scope);
* if a config for a given scope is not defined, then the default config will be
used.
* several standard contexts / scopes have been defined, and various
applications have been modified to attempt using appropriate normalizer in
their context.
* all JUnit tests have been modified, and run successfully.
NUTCH-363 suggests to me that further changes may be required in this area,
perhaps we should combine urlfilters and urlnormalizers into a single subsystem
of url munging - now that we have support for scopes and flexible combinations
of normalizers we could turn URLFilters into a special case of normalizers (or
vice versa, depending on the point of view) ...
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