Package org.springframework.util.function

Class SingletonSupplier<T>

  • Type Parameters:
    T - the type of results supplied by this supplier
    All Implemented Interfaces:
    Supplier<T>
    public class SingletonSupplier<T>
extends Object
implements Supplier<T>
    A Supplier decorator that caches a singleton result and makes it available from get() (nullable) and obtain() (null-safe).

    A SingletonSupplier can be constructed via of factory methods or via constructors that provide a default supplier as a fallback. This is particularly useful for method reference suppliers, falling back to a default supplier for a method that returned null and caching the result.

    Since:
    5.1
    Author:
    Juergen Hoeller

    • Constructor Detail

      • SingletonSupplier

        public SingletonSupplier​(@Nullable
                         T instance,
                         Supplier<? extends T> defaultSupplier)
        Build a SingletonSupplier with the given singleton instance and a default supplier for the case when the instance is null.
        Parameters:
        instance - the singleton instance (potentially null)
        defaultSupplier - the default supplier as a fallback

      • SingletonSupplier

        public SingletonSupplier​(@Nullable
                         Supplier<? extends T> instanceSupplier,
                         Supplier<? extends T> defaultSupplier)
        Build a SingletonSupplier with the given instance supplier and a default supplier for the case when the instance is null.
        Parameters:
        instanceSupplier - the immediate instance supplier
        defaultSupplier - the default supplier as a fallback

    • Method Detail

      • get

        @Nullable
public T get()
        Get the shared singleton instance for this supplier.
        Specified by:
        get in interface Supplier<T>
        Returns:
        the singleton instance (or null if none)

      • obtain

        public T obtain()
        Obtain the shared singleton instance for this supplier.
        Returns:
        the singleton instance (never null)
        Throws:
        IllegalStateException - in case of no instance

      • of

        public static <T> SingletonSupplier<T> of​(T instance)
        Build a SingletonSupplier with the given singleton instance.
        Parameters:
        instance - the singleton instance (never null)
        Returns:
        the singleton supplier (never null)

      • ofNullable

        @Nullable
public static <T> SingletonSupplier<T> ofNullable​(@Nullable
                                                  T instance)
        Build a SingletonSupplier with the given singleton instance.
        Parameters:
        instance - the singleton instance (potentially null)
        Returns:
        the singleton supplier, or null if the instance was null

      • of

        public static <T> SingletonSupplier<T> of​(Supplier<T> supplier)
        Build a SingletonSupplier with the given supplier.
        Parameters:
        supplier - the instance supplier (never null)
        Returns:
        the singleton supplier (never null)

      • ofNullable

        @Nullable
public static <T> SingletonSupplier<T> ofNullable​(@Nullable
                                                  Supplier<T> supplier)
        Build a SingletonSupplier with the given supplier.
        Parameters:
        supplier - the instance supplier (potentially null)
        Returns:
        the singleton supplier, or null if the instance supplier was null