数据来自两个系统时的内存分页算法-优快云博客

本文链接：https://blog.youkuaiyun.com/yjz764297625/article/details/88347719

本文介绍了一种将来自两个不同应用程序的数据集进行内存分页查询并合并的方法。具体实现了根据不同业务时间的数据源进行数据合并，并确保了数据完整性和正确性。

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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;
    }