An incremental work action is one that accepts a single InputChanges parameter. The work action can then query what changed for an input parameter since the last execution to only process the changes. The following example shows a task which reverses the text in each of its input files. It demonstrates how to use InputChanges to only process the changed files.

 abstract class IncrementalReverseTask extends DefaultTask {
     @Incremental
     @InputDirectory
     abstract DirectoryProperty getInputDir()

     @OutputDirectory
     abstract DirectoryProperty getOutputDir()

     @TaskAction
     void execute(InputChanges inputChanges) {
         inputChanges.getFileChanges(inputDir).each { change ->
             if (change.fileType == FileType.DIRECTORY) return

             def targetFile = outputDir.file(change.normalizedPath).get().asFile
             if (change.changeType == ChangeType.REMOVED) {
                 targetFile.delete()
             } else {
                 targetFile.text = change.file.text.reverse()
             }
         }
     }
 }
 

In the case where Gradle is unable to determine which input files need to be reprocessed, then all of the input files will be reported as ChangeType.ADDED. When such a full rebuild happens, the output files of the work are removed prior to executing the work action. Cases where this occurs include:

• There is no history available from a previous execution.
• A non-file input parameter has changed since the previous execution.
• One or more output files have changed since the previous execution.