# Understanding Services and Service Injection

version 8.11

Gradle provides a number of useful services that can be used by custom Gradle types. For example, the WorkerExecutor service can be used by a task to run work in parallel, as seen in the worker API section. The services are made available through service injection.

## Available services

The following services are available for injection:

1. `ObjectFactory` - Allows model objects to be created.

2. `ProjectLayout` - Provides access to key project locations.

3. `BuildLayout` - Provides access to important locations for a Gradle build.

4. `ProviderFactory` - Creates `Provider` instances.

5. `WorkerExecutor` - Allows a task to run work in parallel.

6. `FileSystemOperations` - Allows a task to run operations on the filesystem such as deleting files, copying files or syncing directories.

7. `ArchiveOperations` - Allows a task to run operations on archive files such as ZIP or TAR files.

8. `ExecOperations` - Allows a task to run external processes with dedicated support for running external `java` programs.

9. `ToolingModelBuilderRegistry` - Allows a plugin to registers a Gradle tooling API model.

Out of the above, `ProjectLayout` and `WorkerExecutor` services are only available for injection in project plugins. `BuildLayout` is only available in settings plugins and settings files. `ProjectLayout` is unavailable in Worker API actions.

## 1. `ObjectFactory`

`ObjectFactory` is a service for creating custom Gradle types, allowing you to define nested objects and DSLs in your build logic. It provides methods for creating instances of different types, such as properties (`Property<T>`), collections (`ListProperty<T>`, `SetProperty<T>`, `MapProperty<K, V>`), file-related objects (`RegularFileProperty`, `DirectoryProperty`, `ConfigurableFileCollection`, `ConfigurableFileTree`), and more.

You can obtain an instance of `ObjectFactory` using the `project.objects` property. Here’s a simple example demonstrating how to use `ObjectFactory` to create a property and set its value:

build.gradle.kts

    tasks.register("myObjectFactoryTask") {
        doLast {
            val objectFactory = project.objects
            val myProperty = objectFactory.property(String::class)
            myProperty.set("Hello, Gradle!")
            println(myProperty.get())
        }
    }

build.gradle

    tasks.register("myObjectFactoryTask") {
        doLast {
            def objectFactory = project.objects
            def myProperty = objectFactory.property(String)
            myProperty.set("Hello, Gradle!")
            println myProperty.get()
        }
    }

| It is preferable to let Gradle create objects automatically by using managed properties.

Using `ObjectFactory` to create these objects ensures that they are properly managed by Gradle, especially in terms of configuration avoidance and lazy evaluation. This means that the values of these objects are only calculated when needed, which can improve build performance.

In the following example, a project extension called `DownloadExtension` receives an `ObjectFactory` instance through its constructor. The constructor uses this to create a nested `Resource` object (also a custom Gradle type) and makes this object available through the `resource` property:

DownloadExtension.java

    public class DownloadExtension {
        // A nested instance
        private final Resource resource;

        @Inject
        public DownloadExtension(ObjectFactory objectFactory) {
            // Use an injected ObjectFactory to create a Resource object
            resource = objectFactory.newInstance(Resource.class);
        }

        public Resource getResource() {
            return resource;
        }
    }

    public interface Resource {
        Property<URI> getUri();
    }

Here is another example using `javax.inject.Inject`:

build.gradle.kts

    abstract class MyObjectFactoryTask
    @Inject constructor(private var objectFactory: ObjectFactory) : DefaultTask() {

        @TaskAction
        fun doTaskAction() {
            val outputDirectory = objectFactory.directoryProperty()
            outputDirectory.convention(project.layout.projectDirectory)
            println(outputDirectory.get())
        }
    }

    tasks.register("myInjectedObjectFactoryTask", MyObjectFactoryTask::class) {}

build.gradle

    abstract class MyObjectFactoryTask extends DefaultTask {
        private ObjectFactory objectFactory

        @Inject //@javax.inject.Inject
        MyObjectFactoryTask(ObjectFactory objectFactory) {
            this.objectFactory = objectFactory
        }

        @TaskAction
        void doTaskAction() {
            var outputDirectory = objectFactory.directoryProperty()
            outputDirectory.convention(project.layout.projectDirectory)
            println(outputDirectory.get())
        }
    }

    tasks.register("myInjectedObjectFactoryTask",MyObjectFactoryTask) {}

The `MyObjectFactoryTask` task uses an `ObjectFactory` instance, which is injected into the task’s constructor using the `@Inject` annotation.

## 2. `ProjectLayout`

`ProjectLayout` is a service that provides access to the layout of a Gradle project’s directories and files. It’s part of the `org.gradle.api.file` package and allows you to query the project’s layout to get information about source sets, build directories, and other file-related aspects of the project.

You can obtain a `ProjectLayout` instance from a `Project` object using the `project.layout` property. Here’s a simple example:

build.gradle.kts

    tasks.register("showLayout") {
        doLast {
            val layout = project.layout
            println("Project Directory: ${layout.projectDirectory}")
            println("Build Directory: ${layout.buildDirectory.get()}")
        }
    }

build.gradle

    tasks.register('showLayout') {
        doLast {
            def layout = project.layout
            println "Project Directory: ${layout.projectDirectory}"
            println "Build Directory: ${layout.buildDirectory.get()}"
        }
    }

Here is an example using `javax.inject.Inject`:

build.gradle.kts

    abstract class MyProjectLayoutTask
    @Inject constructor(private var projectLayout: ProjectLayout) : DefaultTask() {

        @TaskAction
        fun doTaskAction() {
            val outputDirectory = projectLayout.projectDirectory
            println(outputDirectory)
        }
    }

    tasks.register("myInjectedProjectLayoutTask", MyProjectLayoutTask::class) {}

build.gradle

    abstract class MyProjectLayoutTask extends DefaultTask {
        private ProjectLayout projectLayout

        @Inject //@javax.inject.Inject
        MyProjectLayoutTask(ProjectLayout projectLayout) {
            this.projectLayout = projectLayout
        }

        @TaskAction
        void doTaskAction() {
            var outputDirectory = projectLayout.projectDirectory
            println(outputDirectory)
        }
    }

    tasks.register("myInjectedProjectLayoutTask",MyProjectLayoutTask) {}

The `MyProjectLayoutTask` task uses a `ProjectLayout` instance, which is injected into the task’s constructor using the `@Inject` annotation.

## 3. `BuildLayout`

`BuildLayout` is a service that provides access to the root and settings directory in a Settings plugin or a Settings script, it is analogous to `ProjectLayout`. It’s part of the `org.gradle.api.file` package to access standard build-wide file system locations as lazily computed value.

| These APIs are currently incubating but eventually should replace existing accessors in Settings, which return eagerly computed locations: `Settings.rootDir` → `Settings.layout.rootDirectory` `Settings.settingsDir` → `Settings.layout.settingsDirectory`

You can obtain a `BuildLayout` instance from a `Settings` object using the `settings.layout` property. Here’s a simple example:

settings.gradle.kts

    println("Root Directory: ${settings.layout.rootDirectory}")
    println("Settings Directory: ${settings.layout.settingsDirectory}")

settings.gradle

    println "Root Directory: ${settings.getLayout().rootDirectory}"
    println "Settings Directory: ${settings.getLayout().settingsDirectory}"

Here is an example using `javax.inject.Inject`:

settings.gradle.kts

    abstract class MyBuildLayoutPlugin @Inject constructor(private val buildLayout: BuildLayout) : Plugin<Settings> {
        override fun apply(settings: Settings) {
            println(buildLayout.rootDirectory)
        }
    }

    apply<MyBuildLayoutPlugin>()

settings.gradle

    abstract class MyBuildLayoutPlugin implements Plugin<Settings> {
        private BuildLayout buildLayout

        @Inject //@javax.inject.Inject
        MyBuildLayoutPlugin(BuildLayout buildLayout) {
            this.buildLayout = buildLayout
        }

        @Override void apply(Settings settings) {
            // the meat and potatoes of the plugin
            println buildLayout.rootDirectory
        }
    }

    apply plugin: MyBuildLayoutPlugin

This code defines a `MyBuildLayoutPlugin` plugin that implements the `Plugin` interface for the `Settings` type. The plugin expects a `BuildLayout` instance to be injected into its constructor using the `@Inject` annotation.

## 4. `ProviderFactory`

`ProviderFactory` is a service that provides methods for creating different types of providers. Providers are used to model values that may be computed lazily in your build scripts.

The `ProviderFactory` interface provides methods for creating various types of providers, including:

- `provider(Callable<T> value)` to create a provider with a value that is lazily computed based on a `Callable`.

- `provider(Provider<T> value)` to create a provider that simply wraps an existing provider.

- `property(Class<T> type)` to create a property provider for a specific type.

- `gradleProperty(Class<T> type)` to create a property provider that reads its value from a Gradle project property.

Here’s a simple example demonstrating the use of `ProviderFactory` using `project.providers`:

build.gradle.kts

    tasks.register("printMessage") {
        doLast {
            val providerFactory = project.providers
            val messageProvider = providerFactory.provider { "Hello, Gradle!" }
            println(messageProvider.get())
        }
    }

build.gradle

    tasks.register('printMessage') {
        doLast {
            def providerFactory = project.providers
            def messageProvider = providerFactory.provider { "Hello, Gradle!" }
            println messageProvider.get()
        }
    }

The task named `printMessage` uses the `ProviderFactory` to create a `provider` that supplies the message string.

Here is an example using `javax.inject.Inject`:

build.gradle.kts

    abstract class MyProviderFactoryTask
    @Inject constructor(private var providerFactory: ProviderFactory) : DefaultTask() {

        @TaskAction
        fun doTaskAction() {
            val outputDirectory = providerFactory.provider { "build/my-file.txt" }
            println(outputDirectory.get())
        }
    }

    tasks.register("myInjectedProviderFactoryTask", MyProviderFactoryTask::class) {}

build.gradle

    abstract class MyProviderFactoryTask extends DefaultTask {
        private ProviderFactory providerFactory

        @Inject //@javax.inject.Inject
        MyProviderFactoryTask(ProviderFactory providerFactory) {
            this.providerFactory = providerFactory
        }

        @TaskAction
        void doTaskAction() {
            var outputDirectory = providerFactory.provider { "build/my-file.txt" }
            println(outputDirectory.get())
        }
    }

    tasks.register("myInjectedProviderFactoryTask",MyProviderFactoryTask) {}

The `ProviderFactory` service is injected into the `MyProviderFactoryTask` task’s constructor using the `@Inject` annotation.

## 5. `WorkerExecutor`

`WorkerExecutor` is a service that allows you to perform parallel execution of tasks using worker processes. This is particularly useful for tasks that perform CPU-intensive or long-running operations, as it allows them to be executed in parallel, improving build performance.

Using `WorkerExecutor`, you can submit units of work (called actions) to be executed in separate worker processes. This helps isolate the work from the main Gradle process, providing better reliability and performance.

Here’s a basic example of how you might use `WorkerExecutor` in a build script:

build.gradle.kts

    abstract class MyWorkAction : WorkAction<WorkParameters.None> {
        private val greeting: String = "Hello from a Worker!"

        override fun execute() {
            println(greeting)
        }
    }

    abstract class MyWorkerTask
    @Inject constructor(private var workerExecutor: WorkerExecutor) : DefaultTask() {
        @get:Input
        abstract val booleanFlag: Property<Boolean>
        @TaskAction
        fun doThings() {
            workerExecutor.noIsolation().submit(MyWorkAction::class.java) {}
        }
    }

    tasks.register("myWorkTask", MyWorkerTask::class) {}

build.gradle

    abstract class MyWorkAction implements WorkAction<WorkParameters.None> {
        private final String greeting;

        @Inject
        public MyWorkAction() {
            this.greeting = "Hello from a Worker!";
        }

        @Override
        public void execute() {
            System.out.println(greeting);
        }
    }

    abstract class MyWorkerTask extends DefaultTask {
        @Input
        abstract Property<Boolean> getBooleanFlag()

        @Inject
        abstract WorkerExecutor getWorkerExecutor()

        @TaskAction
        void doThings() {
            workerExecutor.noIsolation().submit(MyWorkAction) {}
        }
    }

    tasks.register("myWorkTask", MyWorkerTask) {}

See the worker API for more details.

## 6. `FileSystemOperations`

`FileSystemOperations` is a service that provides methods for performing file system operations such as copying, deleting, and creating directories. It is part of the `org.gradle.api.file` package and is typically used in custom tasks or plugins to interact with the file system.

Here is an example using `javax.inject.Inject`:

build.gradle.kts

    abstract class MyFileSystemOperationsTask
    @Inject constructor(private var fileSystemOperations: FileSystemOperations) : DefaultTask() {

        @TaskAction
        fun doTaskAction() {
            fileSystemOperations.copy {
                from("src")
                into("dest")
            }
        }
    }

    tasks.register("myInjectedFileSystemOperationsTask", MyFileSystemOperationsTask::class) {}

build.gradle

    abstract class MyFileSystemOperationsTask extends DefaultTask {
        private FileSystemOperations fileSystemOperations

        @Inject //@javax.inject.Inject
        MyFileSystemOperationsTask(FileSystemOperations fileSystemOperations) {
            this.fileSystemOperations = fileSystemOperations
        }

        @TaskAction
        void doTaskAction() {
            fileSystemOperations.copy {
                from 'src'
                into 'dest'
            }
        }
    }

    tasks.register("myInjectedFileSystemOperationsTask", MyFileSystemOperationsTask) {}

The `FileSystemOperations` service is injected into the `MyFileSystemOperationsTask` task’s constructor using the `@Inject` annotation.

With some ceremony, it is possible to use `FileSystemOperations` in an ad-hoc task defined in a build script:

build.gradle.kts

    interface InjectedFsOps {
        @get:Inject val fs: FileSystemOperations
    }

    tasks.register("myAdHocFileSystemOperationsTask") {
        val injected = project.objects.newInstance<InjectedFsOps>()
        doLast {
            injected.fs.copy {
                from("src")
                into("dest")
            }
        }
    }

build.gradle

    interface InjectedFsOps {
        @Inject //@javax.inject.Inject
        FileSystemOperations getFs()
    }

    tasks.register('myAdHocFileSystemOperationsTask') {
        def injected = project.objects.newInstance(InjectedFsOps)
        doLast {
            injected.fs.copy {
                from 'source'
                into 'destination'
            }
        }
    }

First, you need to declare an interface with a property of type `FileSystemOperations`, here named `InjectedFsOps`, to serve as an injection point. Then call the method `ObjectFactory.newInstance` to generate an implementation of the interface that holds an injected service.

| This is a good time to consider extracting the ad-hoc task into a proper class.

## 7. `ArchiveOperations`

`ArchiveOperations` is a service that provides methods for creating archives, such as ZIP and TAR files. It is part of the `org.gradle.api.tasks.bundling` package and is typically used in custom tasks or plugins to create archive files.

Here is an example using `javax.inject.Inject`:

build.gradle.kts

    abstract class MyArchiveOperationsTask
    @Inject constructor(
        private val archiveOperations: ArchiveOperations,
        private val project: Project
    ) : DefaultTask() {

        @TaskAction
        fun doTaskAction() {
            archiveOperations.zipTree("${project.projectDir}/sources.jar")
        }
    }

    tasks.register("myInjectedArchiveOperationsTask", MyArchiveOperationsTask::class) {}

build.gradle

    abstract class MyArchiveOperationsTask extends DefaultTask {
        private ArchiveOperations archiveOperations

        @Inject //@javax.inject.Inject
        MyArchiveOperationsTask(ArchiveOperations archiveOperations) {
            this.archiveOperations = archiveOperations
        }

        @TaskAction
        void doTaskAction() {
            archiveOperations.zipTree("${projectDir}/sources.jar")
        }
    }

    tasks.register("myInjectedArchiveOperationsTask", MyArchiveOperationsTask) {}

The `ArchiveOperations` service is injected into the `MyArchiveOperationsTask` task’s constructor using the `@Inject` annotation.

With some ceremony, it is possible to use `ArchiveOperations` in an ad-hoc task defined in a build script:

build.gradle.kts

    interface InjectedArcOps {
        @get:Inject val arcOps: ArchiveOperations
    }

    tasks.register("myAdHocArchiveOperationsTask") {
        val injected = project.objects.newInstance<InjectedArcOps>()
        val archiveFile = "${project.projectDir}/sources.jar"
        doLast {
            injected.arcOps.zipTree(archiveFile)
        }
    }

build.gradle

    interface InjectedArcOps {
        @Inject //@javax.inject.Inject
        ArchiveOperations getArcOps()
    }

    tasks.register('myAdHocArchiveOperationsTask') {
        def injected = project.objects.newInstance(InjectedArcOps)
        def archiveFile = "${projectDir}/sources.jar"

        doLast {
            injected.arcOps.zipTree(archiveFile)
        }
    }

First, you need to declare an interface with a property of type `ArchiveOperations`, here named `InjectedArcOps`, to serve as an injection point. Then call the method `ObjectFactory.newInstance` to generate an implementation of the interface that holds an injected service.

| This is a good time to consider extracting the ad-hoc task into a proper class.

## 8. `ExecOperations`

`ExecOperations` is a service that provides methods for executing external processes (commands) from within a build script. It is part of the `org.gradle.process` package and is typically used in custom tasks or plugins to run command-line tools or scripts as part of the build process.

Here is an example using `javax.inject.Inject`:

build.gradle.kts

    abstract class MyExecOperationsTask
    @Inject constructor(private var execOperations: ExecOperations) : DefaultTask() {

        @TaskAction
        fun doTaskAction() {
            execOperations.exec {
                commandLine("ls", "-la")
            }
        }
    }

    tasks.register("myInjectedExecOperationsTask", MyExecOperationsTask::class) {}

build.gradle

    abstract class MyExecOperationsTask extends DefaultTask {
        private ExecOperations execOperations

        @Inject //@javax.inject.Inject
        MyExecOperationsTask(ExecOperations execOperations) {
            this.execOperations = execOperations
        }

        @TaskAction
        void doTaskAction() {
            execOperations.exec {
                commandLine 'ls', '-la'
            }
        }
    }

    tasks.register("myInjectedExecOperationsTask", MyExecOperationsTask) {}

The `ExecOperations` is injected into the `MyExecOperationsTask` task’s constructor using the `@Inject` annotation.

With some ceremony, it is possible to use `ExecOperations` in an ad-hoc task defined in a build script:

build.gradle.kts

    interface InjectedExecOps {
        @get:Inject val execOps: ExecOperations
    }

    tasks.register("myAdHocExecOperationsTask") {
        val injected = project.objects.newInstance<InjectedExecOps>()

        doLast {
            injected.execOps.exec {
                commandLine("ls", "-la")
            }
        }
    }

build.gradle

    interface InjectedExecOps {
        @Inject //@javax.inject.Inject
        ExecOperations getExecOps()
    }

    tasks.register('myAdHocExecOperationsTask') {
        def injected = project.objects.newInstance(InjectedExecOps)

        doLast {
            injected.execOps.exec {
                commandLine 'ls', '-la'
            }
        }
    }

First, you need to declare an interface with a property of type `ExecOperations`, here named `InjectedExecOps`, to serve as an injection point. Then call the method `ObjectFactory.newInstance` to generate an implementation of the interface that holds an injected service.

| This is a good time to consider extracting the ad-hoc task into a proper class.

## 9. `ToolingModelBuilderRegistry`

`ToolingModelBuilderRegistry` is a service that allows you to register custom tooling model builders. Tooling models are used to provide rich IDE integration for Gradle projects, allowing IDEs to understand and work with the project’s structure, dependencies, and other aspects.

The `ToolingModelBuilderRegistry` interface is part of the `org.gradle.tooling.provider.model` package and is typically used in custom Gradle plugins that provide enhanced IDE support.

Here’s a simplified example:

build.gradle.kts

    // Implements the ToolingModelBuilder interface.
    // This interface is used in Gradle to define custom tooling models that can
    // be accessed by IDEs or other tools through the Gradle tooling API.
    class OrtModelBuilder : ToolingModelBuilder {
        private val repositories: MutableMap<String, String> = mutableMapOf()

        private val platformCategories: Set<String> = setOf("platform", "enforced-platform")

        private val visitedDependencies: MutableSet<ModuleComponentIdentifier> = mutableSetOf()
        private val visitedProjects: MutableSet<ModuleVersionIdentifier> = mutableSetOf()

        private val logger = Logging.getLogger(OrtModelBuilder::class.java)
        private val errors: MutableList<String> = mutableListOf()
        private val warnings: MutableList<String> = mutableListOf()

        override fun canBuild(modelName: String): Boolean {
            return false
        }

        override fun buildAll(modelName: String, project: Project): Any? {
            return null
        }
    }

    // Plugin is responsible for registering a custom tooling model builder
    // (OrtModelBuilder) with the ToolingModelBuilderRegistry, which allows
    // IDEs and other tools to access the custom tooling model.
    class OrtModelPlugin(private val registry: ToolingModelBuilderRegistry) : Plugin<Project> {
        override fun apply(project: Project) {
            registry.register(OrtModelBuilder())
        }
    }

build.gradle

    // Implements the ToolingModelBuilder interface.
    // This interface is used in Gradle to define custom tooling models that can
    // be accessed by IDEs or other tools through the Gradle tooling API.
    class OrtModelBuilder implements ToolingModelBuilder {
        private Map<String, String> repositories = [:]

        private Set<String> platformCategories = ["platform", "enforced-platform"]

        private Set<ModuleComponentIdentifier> visitedDependencies = []
        private Set<ModuleVersionIdentifier> visitedProjects = []

        private static final logger = Logging.getLogger(OrtModelBuilder.class)
        private List<String> errors = []
        private List<String> warnings = []

        @Override
        boolean canBuild(String modelName) {
            return false
        }

        @Override
        Object buildAll(String modelName, Project project) {
            return null
        }
    }

    // Plugin is responsible for registering a custom tooling model builder
    // (OrtModelBuilder) with the ToolingModelBuilderRegistry, which allows
    // IDEs and other tools to access the custom tooling model.
    class OrtModelPlugin implements Plugin<Project> {
        ToolingModelBuilderRegistry registry

        OrtModelPlugin(ToolingModelBuilderRegistry registry) {
            this.registry = registry
        }

        void apply(Project project) {
            registry.register(new OrtModelBuilder())
        }
    }

## Constructor injection

There are 2 ways that an object can receive the services that it needs. The first option is to add the service as a parameter of the class constructor. The constructor must be annotated with the `javax.inject.Inject` annotation. Gradle uses the declared type of each constructor parameter to determine the services that the object requires. The order of the constructor parameters and their names are not significant and can be whatever you like.

Here is an example that shows a task type that receives an `ObjectFactory` via its constructor:

Download.java

    public class Download extends DefaultTask {
        private final DirectoryProperty outputDirectory;

        // Inject an ObjectFactory into the constructor
        @Inject
        public Download(ObjectFactory objectFactory) {
            // Use the factory
            outputDirectory = objectFactory.directoryProperty();
        }

        @OutputDirectory
        public DirectoryProperty getOutputDirectory() {
            return outputDirectory;
        }

        @TaskAction
        void run() {
            // ...
        }
    }

## Property injection

Alternatively, a service can be injected by adding a property getter method annotated with the `javax.inject.Inject` annotation to the class. This can be useful, for example, when you cannot change the constructor of the class due to backwards compatibility constraints. This pattern also allows Gradle to defer creation of the service until the getter method is called, rather than when the instance is created. This can help with performance. Gradle uses the declared return type of the getter method to determine the service to make available. The name of the property is not significant and can be whatever you like.

The property getter method must be `public` or `protected`. The method can be `abstract` or, in cases where this isn’t possible, can have a dummy method body. The method body is discarded.

Here is an example that shows a task type that receives a two services via property getter methods:

Download.java

    public abstract class Download extends DefaultTask {
        // Use an abstract getter method
        @Inject
        protected abstract ObjectFactory getObjectFactory();

        // Alternatively, use a getter method with a dummy implementation
        @Inject
        protected WorkerExecutor getWorkerExecutor() {
            // Method body is ignored
            throw new UnsupportedOperationException();
        }

        @TaskAction
        void run() {
            WorkerExecutor workerExecutor = getWorkerExecutor();
            ObjectFactory objectFactory = getObjectFactory();
            // Use the executor and factory ...
        }
    }