T
- Type of value represented by provider@Incubating @NonExtensible public interface Provider<T>
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 provide a value that is mutable and that changes over time.
A typical use of a provider is to pass values from one DSL element to another, e.g. from an extension to a task. Providers also allow expensive computations to be deferred until their value is actually needed, usually at task execution time.
For a provider whose value can be mutated, see Property
.
Do not use Provider<File>
. Use Directory
or RegularFile
instead.
Note: This interface is not intended for implementation by build script or plugin authors. An instance of this class can be created through the factory methods Project.provider(java.util.concurrent.Callable)
or ProviderFactory.provider(java.util.concurrent.Callable)
.
Modifier and Type | Method and Description |
---|---|
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. |
T get()
java.lang.IllegalStateException
.IllegalStateException
- if there is no value present@Nullable T getOrNull()
null
a value is not available.null
T getOrElse(T defaultValue)
<S> Provider<S> map(Transformer<? extends S,? super T> transformer)
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 is 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.
transformer
- The transformer to apply to values. Should not return null
.boolean isPresent()
true
if there is a value present, otherwise false
.true
if there is a value present, otherwise false