Gradle Goodness: Add Incremental Build Support to Custom Tasks with Annotations

In a previous post we learned how we can use the inputs and outputs properties to set properties or files that need to be checked to see if a task is up to date. In this post we learn how a custom task class can use annotations to set input properties, file or files and output files or dir.

For input we can use @Input, @InputFile, @InputFiles or @InputDirectory annotations. Gradle uses the properties with annotations for checking if a task is up to date. Output file or directory can be marked with @OutputFile and @OutputDirectory.

00.task generateVersionFile(type: Generate) {

01.version = '2.0'

02.outputFile = file("$project.buildDir/version.txt")

03.}

04. 

05.task showContents << {

06.println generateVersionFile.outputFile.text

07.}

08.showContents.dependsOn generateVersionFile

09. 

10.class Generate extends DefaultTask {

11.@Input

12.String version

13. 

14.@OutputFile

15.File outputFile

16. 

17.@TaskAction

18.void generate() {

19.def file = getOutputFile()

20.if (!file.isFile()) {

21.file.parentFile.mkdirs()

22.file.createNewFile()

23.}

24.file.write "Version: ${getVersion()}"

25.}

26.}

We can run our task and get the following output:

$ gradle showContents

:generateVersionFile

:showContents

Version: 2.0

 

BUILD SUCCESSFUL

And if we run it again we see the task is now up to date:

$ gradle showContents

:generateVersionFile UP-TO-DATE

:showContents

Version: 2.0

 

BUILD SUCCESSFUL

We can change the version numer in our build script to 2.1 and see the output:

$ gradle showContents

:generateVersionFile

:showContents

Version: 2.1

 

BUILD SUCCESSFUL