Tài liệu Design the jar Task

What are the requirements for a task that creates JARs? A good place to start is to the
command-line tool, jar. At a minimum, our task should replicate the JAR-creating features of
the tool (as opposed to all of the tool's features). This distinction is important. We're not reimplementing
the jar tool, we're creating an operation for our build, satisfying only our build's
requirements. The command-line tool only facilitates reaching that goal. Our build requires
that we create JARs, so our task design should focus on JAR creation, nothing more. Should
we later define a need, for example, to unpackage JARs, we would need an implementation of
those features.
The command-line tool creates a zip-compatible archive with a special directory called
META-INF. It places a special file called MANIFEST.MF into this directory. Without going
into too much detail, we describe JARs as smart zip files: archives capable of not only
packaging a set of files into one file, but also having a type of package-descriptor (the
manifest). At a minimum, our task should create JARs and allow the specification of a userwritten
manifest file, if one exists.
From a build perspective, our design should allow us to create JARs using large sets of files
from multiple directories and file types. Since a JAR maintains the directory structure of the
classfile locations, we may need to modify how certain groups of files are stored within the
JAR file. Experienced Ant users will identify this with file sets and file patterns. (After this
chapter, you'll be able to identify this too!) Cursory research across existing tasks reveals
some with similar file set designs, such as copy and zip.