分页处理，这是做JavaWeb项目中常见的场景。
背景
- 系统架构：SpringCloud分布式
- 持久层：MyBatis
- 前端：前后分离vue.js/bootstrap等.
- 后台提供restful api 接口，前端访问后端接口展示数据。
2种方式提供分页处理方案：
一、直接MyBatis数据库进行分页
controller接口
@ApiImplicitParams({ @ApiImplicitParam(name = "categoryId", value = "支付渠道大类Id", required = false, dataType = "Long", paramType = "query"), @ApiImplicitParam(name = "payChannelId", value = "支付渠道ID", required = false, dataType = "Long", paramType = "query"), @ApiImplicitParam(name = "bankCode", value = "银行名称code", required = false, dataType = "String", paramType = "query"), @ApiImplicitParam(name = "startTime", value = "创建时间起始（示例：2018-09-05）", required = false, dataType = "String", paramType = "query", length = 10), @ApiImplicitParam(name = "endTime", value = "创建时间截止（示例：2018-09-05）", required = false, dataType = "String", paramType = "query", length = 10), @ApiImplicitParam(name = "pageNum", value = "查询开始页", required = true, dataType = "int", paramType = "query"), @ApiImplicitParam(name = "pageSize", value = "查询的页面大小不需要分页则把此值填大一点", required = true, dataType = "int", paramType = "query")}) public PageResult<ChannelBaseDataResp> queryPayChannel( @RequestParam(value = "categoryId", required = false) Long categoryId, @RequestParam(value = "payChannelId", required = false) Long payChannelId, @RequestParam(value = "bankCode", required = false) String bankCode, @RequestParam(value = "startTime", required = false) String startTime, @RequestParam(value = "endTime", required = false) String endTime, @RequestParam(value = "pageNum", required = true) Integer pageNum, @RequestParam(value = "pageSize", required = true) Integer pageSize) { PageResult<ChannelBaseDataResp> response = new PageResult<ChannelBaseDataResp>(); try { int endRowNo = pageNum * pageSize; int beginRowNo = (pageNum - 1) * pageSize + 1; return channelBaseDataService.queryBaseData(categoryId,payChannelId,bankCode,startTime,endTime,beginRowNo,endRowNo); } catch (Exception e) { response = new PageResult<ChannelBaseDataResp>(); if (e instanceof AppException) { response.setCode(((AppException) e).getErrorCode()); response.setResult(((AppException) e).getErrorMsg()); } else { response.setCode(CumReturnCode.SYSTEM_EXCEPTION.code); response.setResult(CumReturnCode.SYSTEM_EXCEPTION.message); } return response; } }
Swagger-ui接口界面如下：
pageNum 和 pageSize 用于前端分页的参数，pageNum：表示页码第几页，pageSize：表示每页展示数据数量。
所有查询条件参数，在mapper-xml里进行处理，再利用数据库oracle本身的rownum行值进行分页。
xml代码：
<select id="queryBaseDataList" resultMap="BaseResultMap"> select ID, PAY_CHANNEL_MAIN_ID, PAY_CHANNEL_ID, BANK_CODE, CREATE_TIME, UPDATE_TIME,UPDATOR from ( select A.*, rownum RN from ( select ID, PAY_CHANNEL_MAIN_ID, PAY_CHANNEL_ID, BANK_CODE, CREATE_TIME, UPDATE_TIME,UPDATOR from CUM_PAY_CHANNEL_BASE <where> <if test="beginCreateTime != null"> CREATE_TIME <![CDATA[ >= ]]> #{beginCreateTime,jdbcType=TIMESTAMP} </if> <if test="endCreateTime != null"> AND CREATE_TIME <![CDATA[ <= ]]> #{endCreateTime,jdbcType=TIMESTAMP} </if> <if test="categoryId != null and categoryId != '' "> AND PAY_CHANNEL_MAIN_ID = #{categoryId,jdbcType=DECIMAL} </if> <if test="payChannelId != null and payChannelId != ''"> AND PAY_CHANNEL_ID = #{payChannelId,jdbcType=DECIMAL} </if> <if test="bankCode != null and bankCode != ''"> AND BANK_CODE = #{bankCode,jdbcType=VARCHAR} </if> </where> order by CREATE_TIME desc ) A where rownum <= #{endRowNo,jdbcType=DECIMAL} ) where RN >= #{beginRowNo,jdbcType=DECIMAL} </select>
优点：直观、方便、易排查问题。 缺点：访问数据库过于频繁，未利用到mybatis本身的缓存优势。
二、Java+缓存分页
这种方法对于前端而言是没变化，无感的。
只是在后端处理稍作变动，思路：
- 先把所有数据记录查询出来
- 数据库实体再次封装为查询实体
- 纯java代码进行分页
- controller接口不变
- service业务处理——>数据库crud操作变动
- 把所有数据库记录查询处理
<select id="queryBaseDataList" resultMap="BaseResultMap"> select ID, PAY_CHANNEL_MAIN_ID, PAY_CHANNEL_ID, BANK_CODE, CREATE_TIME, UPDATE_TIME,UPDATOR from CUM_PAY_CHANNEL_BASE <where> <if test="beginCreateTime != null"> CREATE_TIME <![CDATA[ >= ]]> #{beginCreateTime,jdbcType=TIMESTAMP} </if> <if test="endCreateTime != null"> AND CREATE_TIME <![CDATA[ <= ]]> #{endCreateTime,jdbcType=TIMESTAMP} </if> <if test="categoryId != null and categoryId != '' "> AND PAY_CHANNEL_MAIN_ID = #{categoryId,jdbcType=DECIMAL} </if> <if test="payChannelId != null and payChannelId != ''"> AND PAY_CHANNEL_ID = #{payChannelId,jdbcType=DECIMAL} </if> <if test="bankCode != null and bankCode != ''"> AND BANK_CODE = #{bankCode,jdbcType=VARCHAR} </if> </where> order by CREATE_TIME desc</select>
再按照pageNum和pageSize进行分页处理
//以分页形式输出给前端 List<ChannelRouteGroupResp> resultList = new ArrayList<>(); if(groupRespList.size() >= endRowNo){ for(int i=(beginRowNo-1); i< endRowNo; i++){ resultList.add(groupRespList.get(i)); } }else{ for(int i=(beginRowNo-1); i< groupRespList.size(); i++){ resultList.add(groupRespList.get(i)); } }
优点：利用了mybatis缓存机制，分页查询快速，减少数据库访问次数。
缺点：当数据量大的时候，100W+；在没有条件查询数据库的时候，耗时久
前端分页后的界面展示如下：
