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Chapter 4. Measuring Evolving Software
4.5.1 Jar Extraction
We begin our metric extraction process by first extracting the compiled
class files from inside the set of Java Archives (JAR files) associated
with an individual version. JAR files are a standard packaging and distribution
method used by all Java projects under analysis. The set of
JAR files provided as input into this extraction step was manually constructed
and all known external libraries (also packaged as JAR files)
were tagged manually for removal (cf. Section 3.6.2 for a discussion of
the rationale for removing external libraries).
JAR files were tagged as potential external libraries based on the package
names of classes inside the JAR file. We found that using the
package names was an effective method to detect potential external libraries
because Java developers tend to follow the recommended standard
package naming convention and embed the name of the project, organisation
or team in the package name [235]. For example, all classes
developed by the Hibernate project have a package name that starts
with org.hibernate. We used this common naming convention that is
applied by developers to cluster package names manually (after a simple
sort) and then identify potential third-party JAR files. Once potentially
distinct set of packages was identified, we used a Google search to check
if a distinct project with its own source code repository was available
on the web that matched the package signature identified.
Using this external library identification technique on our data set, we
were able to identify separate project web sites as well as source code
repositories for many third party libraries within the software systems.
Once a distinct open-source project was identified as the primary contributor
of the external library, we created a regular expression to match
the package names of known third party libraries and used this regular
expression to identify and remove external library JAR files from all
versions of the software system. An example of such a pattern was the
one created to identify the use of Apache Commons library where the
package names had a format org.apache.commons.*.
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