java 8单例创建模板

/**
 * 懒加载的单例封装
 * 支持线程安全
 */
final
public class LazySingleton<T> implements Supplier<T> {

    /**
     * 创建对象的lambda，不能返回null
     */
    private final Supplier<T> creator;

    private volatile T instance;

    private LazySingleton(Supplier<T> creator) {
        this.creator = Objects.requireNonNull(creator);
    }

    /**
     * 获取或创建实例
     */
    @Override
    public T get() {
        T ins = instance;
        if (null == ins) {
            synchronized (this) {
                ins = instance;
                if (null == ins) {
                    ins = creator.get();
                    if (null == ins) {
                        throw new IllegalStateException("create instance null");
                    }
                    instance = ins;
                }
            }
        }
        return ins;
    }

    /**
     * 移除已创建的实例
     */
    public T remove() {
        T ins = instance;
        instance = null;
        return ins;
    }

    //

    /**
     * @param creator lazy创建对象的lambda，返回值不能为空
     */
    public static <T> LazySingleton<T> of(Supplier<T> creator) {
        return new LazySingleton<>(creator);
    }

}

使用范例

public class Mian3 {
    static LazySingleton<Mian3> singleton = LazySingleton.of(Mian3::createS3Client);

    public static void main(String[] args) {
        Mian3 mian3 = Mian3.singleton.get();
    }

    public static Mian3 createS3Client() {
        return new Mian3();
    }
}