Dependency downloader

build.gradle

// Downloads dependencies of an artifact in an output directory
//
// Note that it assumes _runtime_ dependencies, and it assumes "Maven compatible" variants.
// For compile time (API) dependencies, or for variant-aware resolution,
// code would have to be updated to set the appropriate resolution attributes.
//
// Usage:
// gradle download --input org.apache.groovy:groovy-json:4.0.1
//
// Optional flags:
//   --output dir : path to output directory
//   --transitive false : without transitives
//   --sources true: also download sources


abstract class Downloader extends DefaultTask {

    @OutputDirectory
    @Optional
    abstract DirectoryProperty getOutputDir()

    @Option(option = "input", description = "GAV coordinates of the library")
    @Input
    abstract Property<String> getCoordinates()

    @Input
    @Optional
    abstract Property<Boolean> getTransitive()

    @Input
    @Optional
    abstract Property<Boolean> getSources()

    private Configuration configuration = project.configurations.detachedConfiguration()

    @Inject
    protected abstract DependencyHandler getDependencies()

    @Inject
    protected abstract FileSystemOperations getFileOperations()

    @Option(option = "output", description = "Output directory")
    private void overrideOutputDir(String dir) {
        outputDir.set(project.file(dir))
    }

    @Option(option = "transitive", description = "Download transitive dependencies")
    protected void overrideTransitive(String flag) {
        transitive.set(Boolean.valueOf(flag))
    }

    @Option(option = "sources", description = "Also download sources")
    protected void overrideSources(String flag) {
        sources.set(Boolean.valueOf(flag))
    }

    @TaskAction
    void download() {
        def cnf = configuration
        def out = outputDir
        configuration.transitive = transitive.get()
        configuration.dependencies.add(dependencies.create(coordinates.get()))
        fileOperations.copy {
            from cnf
            into out
        }
        if (Boolean.TRUE == sources.getOrElse(false)) {
            fileOperations.copy { copy ->
                copy.into out
                def result = dependencies.createArtifactResolutionQuery()
                        .forComponents(cnf.incoming.resolutionResult.allComponents.collect { it.id })
                        .withArtifacts(JvmLibrary, SourcesArtifact)
                        .execute()
                result.resolvedComponents.each {
                    it.getArtifacts(SourcesArtifact).each {
                        if (it instanceof ResolvedArtifactResult) {
                            copy.from it.file
                        }
                    }
                }
            }
        }
        println "Downloaded into ${outputDir.get()}"
    }

}

repositories {
    mavenCentral()
}

tasks.register("download", Downloader) {
    transitive.convention(true)
    outputDir.convention(coordinates.flatMap { layout.buildDirectory.dir("download/$it") })
}