Writing Custom Tasks in Gradle

Writing custom tasks in Gradle is very easy if we understand the lifecycle of its execution https://docs.gradle.org/current/userguide/build_lifecycle.html

Sample custom tasks from build.gradle file 

Copy of the build.gradle available in https://github.com/venkatesh-mohanram/gradle-experiments/blob/master/gradle-custom-tasks/build.gradle


class CustomParentTask extends DefaultTask {
String cv_var1
@TaskAction
void build() {
println "CustomParentTask:build() $cv_var1"
cv_var1 = "CHANGE IN BUILD"
}
}
task customParent(type: CustomParentTask) {
// Initialization
customParent.ext.var1 = 'INITIAL'
cv_var1 = customParent.ext.var1
println "customParent:Initialization"

// Execution
// doFirst -> build() -> doLast
doFirst {
custom.var1 = 'hello'
customParent.ext.var1 = 'World'
cv_var1 = customParent.ext.var1
println "customParent:doFirst"
}
doLast {
println "customParent:doLast"
}
}

class CustomTask extends DefaultTask {
@TaskAction
void build() {
println "CustomTask:build()"
}
}
task custom(type: CustomTask, dependsOn: customParent) {
// Initialization
custom.ext.var1 = ''
println "custom:Initialization"

// Execution
// doFirst -> build() -> doLast
doFirst {
println "custom:doFirst $custom.ext.var1 $customParent.var1"
}
doLast {
println "custom:doLast"
}
}

Execution of the custom task will result in the following output; if we notice the first execution all are the initialization code, followed by the execution phase. Within execution, it executes in the following order doFirst, class method and finally doLast

$ gradle custom

> Configure project :
customParent:Initialization
custom:Initialization

> Task :customParent
customParent:doFirst
CustomParentTask:build() World
customParent:doLast

> Task :custom
custom:doFirst hello World
CustomTask:build()
custom:doLast

BUILD SUCCESSFUL in 2s
2 actionable tasks: 2 executed