数据来自两个系统时的内存分页算法

业务数据来自a-app与b-app，其中a-app中数据的业务时间早于b-app，现在需要对这两个来源的数据做内存分页查询。

public ResultGson<ProductPaginationBean> mergePaginationQuery(int pageNo, int pageSize) {
        ResultGson<ProductPaginationBean> productPaginationResultGson = new ResultGson<ProductPaginationBean>("000", "success", null);
        ResultGson<ProductPaginationBean> paginationOneResultGson = paginationOneQuery(pageNo, pageSize);
        ResultGson<ProductPaginationBean> paginationTwoBeanResultGson = paginationSecondQuery(pageNo, pageSize);
        int firstTotalCount = paginationOneResultGson.getData().getTotalCount();
        int secondTotalCount = paginationTwoBeanResultGson.getData().getTotalCount();
        int totalCount = firstTotalCount + secondTotalCount;

        int firstTotalPage = firstTotalCount / pageSize;
        int firstMode = firstTotalCount % pageSize;

        if (firstTotalPage > pageNo) {
            ProductPaginationBean productPaginationBean = new ProductPaginationBean(totalCount, paginationOneResultGson.getData().getProductDTOList());
            productPaginationResultGson.setData(productPaginationBean);
            return productPaginationResultGson;
        }

        if (firstTotalPage < pageNo) {
            ResultGson<ProductPaginationBean> productPaginationFirstResultGson = paginationSecondQuery(pageNo - firstTotalPage -1, pageSize);
            ResultGson<ProductPaginationBean> productPaginationSecondResultGson = paginationSecondQuery(pageNo - firstTotalPage, pageSize);
            List<ProductDTO> mergedProductList = mergeDataAfterRemoveDataOfFirstList(pageSize-firstMode, productPaginationFirstResultGson.getData().getProductDTOList(), productPaginationSecondResultGson.getData().getProductDTOList());
            ProductPaginationBean productPaginationBean = new ProductPaginationBean(totalCount, mergedProductList);
            productPaginationResultGson.setData(productPaginationBean);
            return productPaginationResultGson;
        }

        if (firstTotalPage== pageNo) {
            paginationOneResultGson = paginationOneQuery(pageNo, pageSize);
            paginationTwoBeanResultGson = paginationSecondQuery(0, pageSize);
            List<ProductDTO> productDTOList = mergeDataDeleteSomeIfPossible(paginationOneResultGson.getData().getProductDTOList() , paginationTwoBeanResultGson.getData().getProductDTOList() , pageSize);
            ProductPaginationBean productPaginationBean = new ProductPaginationBean(totalCount, productDTOList);
            productPaginationResultGson.setData(productPaginationBean);
            return productPaginationResultGson;
        }


        return productPaginationResultGson;
    }

    private List<ProductDTO> mergeDataAfterRemoveDataOfFirstList(int removeSize, List<ProductDTO> firstProductList, List<ProductDTO> secondProductList) {
        List<ProductDTO> resultProductList = new ArrayList<>();
        if (firstProductList.size() > removeSize) {
            resultProductList.addAll(firstProductList.subList(removeSize, firstProductList.size()));
        }

        int cutSize = removeSize > secondProductList.size() ? secondProductList.size() : removeSize;

        resultProductList.addAll(secondProductList.subList(0, cutSize));
        return resultProductList;
    }

    private List<ProductDTO> mergeDataDeleteSomeIfPossible(List<ProductDTO> firstProductList, List<ProductDTO> secondProductList, int pageSize) {
        List<ProductDTO> resultProductList = new ArrayList<>();
        resultProductList.addAll(firstProductList);
        resultProductList.addAll(secondProductList);

        if (resultProductList.size() > pageSize) {
            resultProductList = resultProductList.subList(0, pageSize);
        }

        return resultProductList;
    }