分页处理，这是做JavaWeb项目中常见的场景。
背景：
1.系统架构：SpringCloud分布式
2.持久层：MyBatis
3.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：
1.先把所有数据记录查询出来
2.数据库实体再次封装为查询实体
3.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：
