Benoit Perrot created MSHADE-205:
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Summary: Better use of ClazzpathUnit for improved jar minimization
Key: MSHADE-205
URL: https://issues.apache.org/jira/browse/MSHADE-205
Project: Maven Shade Plugin
Issue Type: Improvement
Affects Versions: 2.4.1
Reporter: Benoit Perrot
Minimizing an uber-jar consists in assessing the relevance of classes of all
artifacts on which the project being process depends: when a class is not
identified as being used, it is simply removed from the final jar.
To support implicit uses (eg. dynamicaly loaded classes), it is possible to
explicitly tell the maven-shade-plugin that a classes must be specifically
included.
The algorithm for assessing the relevance of these classes is roughly the
following:
{code}
// All classes are initially considered as irrelevant
for each artifact in dependencies:
for each class in the set of irrelevant ones:
if artifact contains class && class is specifically included:
remove class from the set of irrelevant ones
{code}
Checking whether an artifact contains a class or not is done by invoking the
{{getClazzes()}} method on {{org.vafer.jdependency}} {{ClazzpathUnit}}.
Contrary to what its name suggests, this method is not as harmless as it seems:
it actually builds a hash set and fills it up with the entire set of classes in
a given jar _each time it is called_. (See ClazzpathUnit.java, line 36 at the
time of writing)
The instance of {{ClazzpathUnit}} is not modified during the iteration, so
simply caching the result of this {{getClazzes()}} would avoid the creation and
filling of the said set, and greatly increase the speed of the process.
The improvement obviously depends on the number of artifacts used by the
project being processed, and the number of classes inside them. We observed
very significant gains on our industrial cases.
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