源码分析：Spring 单例轮子 - SingletonSupplier

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public class MyTest {
    // 2024-05-10 16:30
    public static void main(String[] args) throws Throwable {
        
        SingletonSupplier<MyTest> supplier = SingletonSupplier.of(MyTest::new);
        supplier.get();
        
    }
}

SingletonSupplier源码

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/**
 * @since 5.1
 */
public class SingletonSupplier<T> implements Supplier<T> {

	@Nullable
	private final Supplier<? extends T> instanceSupplier;

	@Nullable
	private final Supplier<? extends T> defaultSupplier;

	@Nullable
	private volatile T singletonInstance;
	
	// ...

	@Override
	@Nullable
	public T get() {
		T instance = this.singletonInstance;
		if (instance == null) {
			synchronized (this) {
				instance = this.singletonInstance;
				if (instance == null) {
					if (this.instanceSupplier != null) {
						instance = this.instanceSupplier.get();
					}
					if (instance == null && this.defaultSupplier != null) {
						instance = this.defaultSupplier.get();
					}
					this.singletonInstance = instance;
				}
			}
		}
		return instance;
	}

	public T obtain() {
		T instance = get();
		Assert.state(instance != null, "No instance from Supplier");
		return instance;
	}
    // ...
}