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