org.springframework.util.function

Class SingletonSupplier<T>

java.lang.Object

org.springframework.util.function.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 Summary

Constructors

Constructor and Description
SingletonSupplier(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.
SingletonSupplier(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.

Method Summary

Modifier and Type	Method and Description
T	get() Get the shared singleton instance for this supplier.
T	obtain() Obtain the shared singleton instance for this supplier.
static <T> SingletonSupplier<T>	of(Supplier<T> supplier) Build a SingletonSupplier with the given supplier.
static <T> SingletonSupplier<T>	of(T instance) Build a SingletonSupplier with the given singleton instance.
static <T> SingletonSupplier<T>	ofNullable(Supplier<T> supplier) Build a SingletonSupplier with the given supplier.
static <T> SingletonSupplier<T>	ofNullable(T instance) Build a SingletonSupplier with the given singleton instance.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

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