Task dependencies

Remarks#

doLast

Note, that in a gradle 3.x more idiomatic way task definition: using explicit doLast{closure} notation instead “leftShift”(<<) operator preferable.(leftShift has been deprecated in a gradle 3.2 is scheduled to be removed in gradle 5.0.)

task oldStyle << {
    println 'Deprecated style task'
 }

is equivalent to:

task newStyle {
    doLast {
    println 'Deprecated style task'
    }
 }

Adding dependencies using task names

We can change the tasks execution order with the dependsOn method.

task A << {
    println 'Hello from A'
}
task B(dependsOn: A) << {
    println "Hello from B"
}

Adding `dependsOn: causes:

task B depends on task A
Gradle to execute A task everytime before the B task execution.

And the output is:

> gradle -q B
Hello from A
Hello from B

Adding dependencies from another project

project('projectA') {
    task A(dependsOn: ':projectB:B') << {
        println 'Hello from A'
    }
}

project('projectB') {
    task B << {
        println 'Hello from B'
    }
}

To refer to a task in another project, you prefix the name of the task with the path of the project it belongs to :projectB:B.

And the output is:

> gradle -q B
Hello from A
Hello from B

Adding dependency using task object

task A << {
    println 'Hello from A'
}

task B << {
    println 'Hello from B'
}

B.dependsOn A

It is an alternative way to define the dependency instead of using the task name.

And the output is the same:

> gradle -q B
Hello from A
Hello from B

Adding multiple dependencies

You can add multiple dependencies.

task A << {
    println 'Hello from A'
}

task B << {
    println 'Hello from B'
}

task C << {
    println 'Hello from C'
}

task D << {
    println 'Hello from D'
}

Now you can define a set of dependencies:

B.dependsOn A
C.dependsOn B
D.dependsOn C

The output is:

> gradle -q D
Hello from A
Hello from B
Hello from C
Hello from D

Other example:

B.dependsOn A 
D.dependsOn B
D.dependsOn C

The output is:

> gradle -q D
Hello from A
Hello from B
Hello from C
Hello from D

Multiple dependencies with the dependsOn method

You can add multiple dependencies.

task A << {
    println 'Hello from A'
}

task B(dependsOn: A) << {
    println 'Hello from B'
}

task C << {
    println 'Hello from C'
}

task D(dependsOn: ['B', 'C'] << {
    println 'Hello from D'
}

The output is:

> gradle -q D
Hello from A
Hello from B
Hello from C
Hello from D