Interface Provider<T>

Type Parameters:
T - Type of value represented by provider
All Known Subinterfaces:
BinaryProvider<T>, DirectoryProperty, ListProperty<T>, MapProperty<K,V>, NamedDomainObjectProvider<T>, Property<T>, RegularFileProperty, SetProperty<T>, TaskProvider<T>
@NonExtensible public interface Provider<T>
A container object that provides a value of a specific type. The value can be retrieved using one of the query methods such as get() or getOrNull().

A provider may not always have a value available, for example when the value may not yet be known but will be known at some point in the future. When a value is not available, isPresent() returns false and retrieving the value will fail with an exception.

A provider may not always provide the same value. Although there are no methods on this interface to change the value, the provider implementation may be mutable or use values from some changing source. A provider may also provide a value that is mutable and that changes over time.

A provider may be used to represent a task output. Such a provider carries information about which task produces its value. When attached to a task input, this allows Gradle to automatically add dependencies between tasks based on the values they use as inputs and produce as outputs.

A typical use of a provider is to pass values from one Gradle model element to another, e.g. from a project extension to a task, or between tasks. Providers also allow expensive computations to be deferred until their value is actually needed, usually at task execution time.

There are a number of ways to create a Provider instance. Some common methods:

For a provider whose value can be mutated, see Property and the methods on ObjectFactory.

Note: This interface is not intended for implementation by build script or plugin authors.

Since:
4.0

  • Method Summary

    Modifier and Type
    Method
    Description
    <S> Provider<S>
    flatMap(Transformer<? extends Provider<? extends S>, ? super T> transformer)
    Returns a new Provider from the value of this provider transformed using the given function.
    T
    get()
    Returns the value of this provider if it has a value present, otherwise throws java.lang.IllegalStateException.
    T
    getOrElse(T defaultValue)
    Returns the value of this provider if it has a value present.
    T
    getOrNull()
    Returns the value of this provider if it has a value present.
    boolean
    isPresent()
    Returns true if there is a value present, otherwise false.
    <S> Provider<S>
    map(Transformer<? extends S, ? super T> transformer)
    Returns a new Provider whose value is the value of this provider transformed using the given function.

  • Method Details

    • get

      T get()
      Returns the value of this provider if it has a value present, otherwise throws java.lang.IllegalStateException.
      Returns:
      the current value of this provider.
      Throws:
      IllegalStateException - if there is no value present

    • getOrNull

      @Nullable T getOrNull()
      Returns the value of this provider if it has a value present. Returns null a value is not available.
      Returns:
      the value or null

    • getOrElse

      T getOrElse(T defaultValue)
      Returns the value of this provider if it has a value present. Returns the given default value if a value is not available.
      Returns:
      the value or the default value.
      Since:
      4.3

    • map

      <S> Provider<S> map(Transformer<? extends S, ? super T> transformer)
      Returns a new Provider whose value is the value of this provider transformed using the given function.

      The new provider will be live, so that each time it is queried, it queries this provider and applies the transformation to the result. Whenever this provider has no value, the new provider will also have no value.

      Note that the new provider may cache the result of the transformations and so there is no guarantee that the transformer will be called on every query of the new provider. The new provider will apply the transformation lazily, and calculate the value for the new provider when queried.

      When this provider represents a task or the output of a task, the new provider will be considered an output of the task and will carry dependency information that Gradle can use to automatically attach task dependencies to tasks that use the new provider for input values.

      Parameters:
      transformer - The transformer to apply to values. Should not return null.
      Since:
      4.3

    • flatMap

      @Incubating <S> Provider<S> flatMap(Transformer<? extends Provider<? extends S>, ? super T> transformer)
      Returns a new Provider from the value of this provider transformed using the given function.

      The new provider will be live, so that each time it is queried, it queries this provider and applies the transformation to the result. Whenever this provider has no value, the new provider will also have no value.

      Note that the new provider may cache the result of the transformations and so there is no guarantee that the transformer will be called on every query of the new provider. The new provider will apply the transformation lazily, and calculate the value for the new provider when queried.

      Any task details associated with this provider are ignored. The new provider will use whatever task details are associated with the return value of the function.

      Parameters:
      transformer - The transformer to apply to values. Should not return null.
      Since:
      5.0

    • isPresent

      boolean isPresent()
      Returns true if there is a value present, otherwise false.
      Returns:
      true if there is a value present, otherwise false