单例保存大体积的数据到内存中

public class DataHolder {

    Map<String, WeakReference<Object>> data = new HashMap<>();

    private static final DataHolder holder = new DataHolder();

    public static DataHolder getInstance() {
        return holder;
    }

    public void save(String id, Object object) {
        data.put(id, new WeakReference<Object>(object));
    }

    public Object retrieve(String id) {
        WeakReference<Object> objectWeakReference = data.get(id);
        return objectWeakReference.get();
    }

}