记一次按天数计算数据总条数的分页。

主要代码：

public static PagingModel getPagingModel(int page, int pageSize, int count) {// 第一个被dataCount整除的位置（0 ~ pageSize之间的值），也就是firstCount的值int firstValue = 0,// 最后一个被dataCount整除的位置（0 ~ pageSize之间的值），被pageSize减去后，就是lastCount的值lastValue = 0;// 数据库起始索引int offset = 0,// 数据库查询条数limit = 0,// 倍数，用于统计可显示全部天数的数据(表现为dataCount条新数据)的元数据条数times = 0,// 当上一页有数据未完全显示时，firstCount为未完全显示的剩余条数firstCount = 0,// 当本页有数据不能被完全显示时，lastCount为这些数据应显示的条数lastCount = 0,// 开始行数startRow = 0,// 结束行数endRow = 0;// 此公式原用于计算数据库中的起始索引，即LIMIT offset, count; 现由于数据总条数的变动，只能作为临时参考。int index = (page - 1) * pageSize;// 原本为数据库中根据LIMIT offset, count;查询到的第一行的行号。startRow = index + 1;// 原本为数据库中根据LIMIT offset, count;查询到的最后一行的行号。endRow = page * pageSize;/** * 计算开始行到结束行之间（包含），递增，第一个能被dataCount整除的位置（索引从1开始），可直接作为firstCount的值 */for (int i = startRow, j = 1; i <= endRow; i++, j++) {if (i % count == 0) {firstValue = j;break;}}/** * 计算结束行到开始行之间（包含），递减，第一个能被dataCount整除的位置（索引从pageSize开始） */for (int i = endRow, j = pageSize; i >= startRow; i--, j--) {if (i % count == 0) {lastValue = j;break;}}firstCount = firstValue; // 赋值lastCount = pageSize - lastValue; // 赋值times = (lastValue - firstValue) / count; // 计算倍数/* * 如果firstCount和dataCount相等，就将它放入可被完全显示的数目中 */if (firstCount == count) {firstCount = 0;times++;}// 因为总数据多了dataCount倍，现有的offset应该要在原有的基础上除以dataCountoffset = index / count;// 计算limit的条数limit = (firstCount > 0 ? 1 : 0) + times + (lastCount > 0 ? 1 : 0);System.out.println("firstValue=" + firstValue + "&lastValue=" + lastValue + "&startRow=" + startRow + "&endRow="+ endRow + "&page=" + page + "&firstCount=" + firstCount + "×=" + times + "&lastCount=" + lastCount+ "&offset=" + offset + "&limit=" + limit);PagingModel model = new PagingModel();model.setFirst(firstCount);model.setTimes(times);model.setLast(lastCount);model.setOffset(offset);model.setLimit(limit);return model;}

模型

public static class PagingModel {private int first;private int times;private int last;private int offset;private int limit;public int getFirst() {return first;}public void setFirst(int first) {this.first = first;}public int getTimes() {return times;}public void setTimes(int times) {this.times = times;}public int getLast() {return last;}public void setLast(int last) {this.last = last;}public int getOffset() {return offset;}public void setOffset(int offset) {this.offset = offset;}public int getLimit() {return limit;}public void setLimit(int limit) {this.limit = limit;}}

测试：

public static void main(String[] args) {int page = 1, // 当前页数pageSize = 20, // 每页显示数据days = 7; // 查询天数int count = days; // 每条元数据对应新数据条数int metadataCount = 50;// 假设数据库中有50条数据// 每条数据库中的元数据都会产生dataCount条数据，即总条数为totalCount = metadataCount * countint totalCount = metadataCount * count;// 计算总页数int totalPage = (totalCount + pageSize - 1) / pageSize;PagingModel pagingModel;List<ResultModel> subMetadatas;List<ResultModel> results;for (page = 1; page <= totalPage; page++) {pagingModel = getPagingModel(page, pageSize, count);List<ResultModel> metadatas = new ArrayList<>(metadataCount);ResultModel resultModel;for (int i = 0; i < metadataCount; i++) {resultModel = new ResultModel();resultModel.setId(10000 + i);metadatas.add(resultModel);}int fromIndex = pagingModel.getOffset();int toIndex = pagingModel.getOffset() + pagingModel.getLimit();if (toIndex > metadataCount) {toIndex = metadataCount;}// 慎用subListsubMetadatas = metadatas.subList(fromIndex, toIndex);results = new ArrayList<>(pageSize);int size = subMetadatas.size();if (pagingModel.getFirst() > 0 && size > 0) {results.addAll(createFirstData(count, pagingModel.getFirst(), subMetadatas.get(0)));subMetadatas.remove(0); // 直接从集合里删除更方便计算}int times = pagingModel.getTimes();size = subMetadatas.size();if (times > 0 && size > 0) {// 慎用subListif (times > size) {times = size;}results.addAll(createMiddleData(count, subMetadatas.subList(0, times)));// 慎用subListif (times >= size) {subMetadatas.clear();}}size = subMetadatas.size();if (pagingModel.getLast() > 0 && size > 0) {results.addAll(createLastData(pagingModel, subMetadatas.get(size - 1)));subMetadatas.remove(size - 1); // 直接从集合里删除更方便计算}System.out.println("*********************第" + page + "页数据***************************");System.out.println("序号\tID\t日期");int i = 1;for (ResultModel model : results) {System.out.println((i++) + "\t" + model);}System.out.println("***********************结束************************");System.out.println();}}static List<ResultModel> createFirstData(int count, int firstCount, ResultModel first) {List<ResultModel> results = new ArrayList<>(firstCount);// 并依次往前取昨天，前天的时间LocalDate localDate = LocalDate.now().minusDays(count - firstCount);ResultModel resultModel = null;for (int i = 0; i < firstCount; i++) {resultModel = first.clone();resultModel.setDate(DateTimeFormatter.ISO_DATE.format(localDate.minusDays(i)));results.add(resultModel);}return results;}static List<ResultModel> createMiddleData(int count, List<ResultModel> datas) {List<ResultModel> results = new ArrayList<>(datas.size());// 显示全部数据，日期是当天开始由后往前排序LocalDate localDate = LocalDate.now();ResultModel resultModel = null;for (ResultModel model : datas) {for (int i = 0; i < count; i++) {resultModel = model.clone();resultModel.setDate(DateTimeFormatter.ISO_DATE.format(localDate.minusDays(i)));results.add(resultModel);}}return results;}static List<ResultModel> createLastData(PagingModel pagingModel, ResultModel last) {List<ResultModel> results = new ArrayList<>(pagingModel.getLast());// last为末尾元数据截取，日期是当天开始由后往前排序LocalDate localDate = LocalDate.now();ResultModel resultModel = null;for (int i = 0; i < pagingModel.getLast(); i++) {resultModel = last.clone();resultModel.setDate(DateTimeFormatter.ISO_DATE.format(localDate.minusDays(i)));results.add(resultModel);}return results;}public static class ResultModel implements Cloneable {private int id;private String date;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getDate() {return date;}public void setDate(String date) {this.date = date;}@Overrideprotected ResultModel clone() {try {return (ResultModel) super.clone();} catch (CloneNotSupportedException e) {ResultModel model = new ResultModel();model.id = id;model.date = date;return model;}}@Overridepublic String toString() {return id + "\t" + date;}}