Gradle Command from configurations.compile.collect

Question

I stumbled upon one article about how to make fat jar files in Gradle.

jar {
    from configurations.compile.collect { it.isDirectory() ? it : zipTree(it) }
}

My questions are

1. what is the jar element? Is it a way to declare properties. As I understand, I can define properties as follows:

   prop1{ prop2{ prop3.prop4=5 } }

which is equivalent to: prop1.prop2.prop3.prop4=5

2. the from statement: Is it a method? I mean is it from (params).

I also found an article about ConfigurationContainer: https://gradle.org/docs/current/javadoc/org/gradle/api/artifacts/ConfigurationContainer.html.

However, I can't link the information to make a full picture here.

Answer 1

1. jar is a task name. It has nothing to do with properties. Tasks are the basic building block of every Gradle build. It is equivalent to tasks.jar

2. from is a method of the CopySpec class. Many tasks extend from the CopySpec class and inherit the from method.

configurations.compile is a reference to the all of the artifacts defined in the compile configuration.

.collect {} is a method call with one argument that is a closure. {} is an empty closure.

{ it.isDirectory() ? it : zipTree(it) } is the closure (aka function) that returns a collection of files to be include in the JAR. it is the default argument of every closure that in the case, will be a JAR artifact instance from configurations.compile or a local file path instance. It could be a file path because configurations support both JARS and local files system paths of compiled .class files.

The logic in the closure is in the form of <conditional> ? <A> : <B> and means if <conditional> then return <A> else return <B>.

The conditional it.isDirectory() evaluates to True if the it variable is a directory. So if it is a directory we return it. If it's not a directory, then the code assumes it's a JAR.

zipTree(it) is a method that extracts all the files from a JAR and returns them as a collection.

All of the file (directories or exploded JARS) are returned from the closure and then "combined" by collect into a single collection (e.g. FileTree).