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Common utils for BOX projects.
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package commons.box.app;

import commons.box.app.func.DataSupplier;

/**
 * 单例模式对象 使用时应该声明为 final 字段 然后通过 doGet 方法获取值
 */
public final class SObject implements DataSupplier {
    private final Object lock = new SafeObject<>();
    private final DataSupplier supplier;
    private transient volatile SafeObject object;

    /**
     * 构建无 supplier 的单例模式对象 此时仅可通过 doGet(Supplier supplier) 方法获取值
     */
    public SObject() {
        this.supplier = null;
    }

    /**
     * 构建 对象值通过 Supplier 获取
     * 
     * supplier.doGet() 返回值必须不为空，否则每次调用时均会请求 supplier
     *
     * @param supplier
     */
    public SObject(DataSupplier supplier) {
        this.supplier = supplier;
    }

    /**
     * 构建 直接生成实例
     *
     * @param obj
     */
    public SObject(T obj) {
        this.supplier = () -> obj;
        this.object = new SafeObject<>(obj);
    }

    /**
     * 通过定义的 supplier 获取数据 单例模式
     *
     * @return
     */
    public T get() {
        return this.get(this.supplier);
    }

    /**
     * 通过给定的 supplier 获取数据 单例模式
     * 

     * 注意，此处定义的 supplier 仅变量不存在时才会调用 并非每次均调用
     * 
     * supplier.doGet() 返回值必须不为空，否则每次调用时均会请求 supplier
     *
     * @param supplier
     * @return
     */
    public T get(DataSupplier supplier) {
        if (this.object == null) {
            if (supplier == null) throw AppError.error("单例对象未定义 supplier");
            synchronized (this.lock) {
                if (this.object == null) this.object = new SafeObject<>(supplier.get());
            }
        }

        return (this.object != null) ? this.object.getObject() : null;
    }

    /**
     * 直接设置值
     *
     * @param obj
     */
    public void set(T obj) {
        synchronized (this.lock) {
            this.object = new SafeObject<>(obj);
        }
    }

    /**
     *
     */
    public T raw() {
        return (this.object != null) ? this.object.getObject() : null;
    }

    /**
     * 清除当前值
     */
    public void clear() {
        synchronized (this.lock) {
            this.object = null;
        }
    }
}