Mybatis-Plus 分页功能实现流程 Mybatis 自带分页功能，但是该分页功能是基于内存的分页，也就是会讲所有符合条件的数据查询出来，然后在从内存中获取当前页的信息，这种方式在数据量大的情况下会存在严重的性能问题。我们通过 Mybatis-Plus 自带的分页插件可以很好的解决这个问题，实现步骤记录如下：1、 添加配置类，示例内容如下：package com.paratera.protect.config; import com.baomidou.mybatisplus.annotation.DbType; import com.baomidou.mybatisplus.extension.plugins.MybatisPlusInterceptor; import com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; /** * Mybatis Plus 配置类，主要用于继承分页插件 * @author 朱治龙 * @date 2023-10-19 23:14:00 */ @Configuration public class MyBatisPlusConfig { @Bean public MybatisPlusInterceptor mybatisPlusInterceptor() { MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor(); // 分页插件 interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL)); return interceptor; } } 2、使用分页方法查询2.1、selectPage2.1.1 示例代码 @Test void testSelectPage() { QueryWrapper<Staff> qw = Wrappers.query(); qw.ge("age", 30); Page<Staff> page = new Page<Staff>(1, 2); // 不查记录数 // page.setSearchCount(false); Page<Staff> pageData = staffMapper.selectPage(page, qw); System.out.println("总页数：" + pageData.getPages()); System.out.println("总记录数：" + pageData.getTotal()); pageData.getRecords().forEach(System.out::println); }2.1.2 查询结果DEBUG==> Preparing: SELECT COUNT(*) AS total FROM staff WHERE (age >= ?) DEBUG==> Parameters: 30(Integer) TRACE<== Columns: total TRACE<== Row: 4 DEBUG<== Total: 1 DEBUG==> Preparing: SELECT id,name,age,email,mobile,manager_id,create_time FROM staff WHERE (age >= ?) LIMIT ? DEBUG==> Parameters: 30(Integer), 2(Long) TRACE<== Columns: id, name, age, email, mobile, manager_id, create_time TRACE<== Row: 1087982257332887553, 大boss, 40, 001@paratera.com, 13888886666, null, 2019-01-11 14:20:20 TRACE<== Row: 1094590409767661570, 张雨琪, 31, zjq@blsc.com, 18684700070, 1088248166370832385, 2019-01-14 09:15:15 DEBUG<== Total: 2 总页数：2 总记录数：4 Staff(id=1087982257332887553, name=大boss, age=40, email=001@paratera.com, mobile=13888886666, managerId=null, createTime=2019-01-11T14:20:20) Staff(id=1094590409767661570, name=张雨琪, age=31, email=zjq@blsc.com, mobile=18684700070, managerId=1088248166370832385, createTime=2019-01-14T09:15:15) 2.2、selectMapsPage2.2.1 示例代码 @Test void testSelectMapsPage() { QueryWrapper<Staff> qw = Wrappers.query(); qw.ge("age", 30); Page<Map<String, Object>> page2 = new Page<>(1, 2); Page<Map<String, Object>> pageData2 = staffMapper.selectMapsPage(page2, qw); System.out.println("总页数：" + pageData2.getPages()); System.out.println("总记录数：" + pageData2.getTotal()); pageData2.getRecords().forEach(System.out::println); }2.2.2 查询结果DEBUG==> Preparing: SELECT COUNT(*) AS total FROM staff WHERE (age >= ?) DEBUG==> Parameters: 30(Integer) TRACE<== Columns: total TRACE<== Row: 4 DEBUG<== Total: 1 DEBUG==> Preparing: SELECT id,name,age,email,mobile,manager_id,create_time FROM staff WHERE (age >= ?) LIMIT ? DEBUG==> Parameters: 30(Integer), 2(Long) TRACE<== Columns: id, name, age, email, mobile, manager_id, create_time TRACE<== Row: 1087982257332887553, 大boss, 40, 001@paratera.com, 13888886666, null, 2019-01-11 14:20:20 TRACE<== Row: 1094590409767661570, 张雨琪, 31, zjq@blsc.com, 18684700070, 1088248166370832385, 2019-01-14 09:15:15 DEBUG<== Total: 2 总页数：2 总记录数：4 {create_time=2019-01-11T14:20:20, name=大boss, mobile=13888886666, id=1087982257332887553, age=40, email=001@paratera.com} {create_time=2019-01-14T09:15:15, manager_id=1088248166370832385, name=张雨琪, mobile=18684700070, id=1094590409767661570, age=31, email=zjq@blsc.com} 3、附加说明使用分页插件查询时默认是会执行两条 SQL,一条获取当前页的数据，一条获取总记录数。在某些场景下(如瀑布流模式)，只需要获取当前页的内容即可，不需要总记录数相关分页数值，此时可在创建 Page 时，第三个参数给值为 false：Page(long current, long size, boolean searchCount)。也可使用 page.setSearchCount(false);

Mybatis-Plus 自定义SQL 有的时候使用条件构造器自定义SQL满足不了我们的需求，我们既想使用 Wrapper,又想使用SQL,MP 对这种方式也提供了支持，MP 版本号应≥3.0.7。下面是该方案的实现记录：实现方案一：Mapper接口中使用@Select注解1、Mapper 示例代码如下：import com.baomidou.mybatisplus.core.conditions.Wrapper; import com.baomidou.mybatisplus.core.mapper.BaseMapper; import com.baomidou.mybatisplus.core.toolkit.Constants; import com.paratera.protect.entity.Staff; import org.apache.ibatis.annotations.Param; import org.apache.ibatis.annotations.Select; import java.util.List; /** * @author 朱治龙 * @date 2023-10-17 11:46:00 */ public interface StaffMapper extends BaseMapper<Staff> { @Select("select * from staff ${ew.customSqlSegment}") List<Staff> selectAll(@Param(Constants.WRAPPER)Wrapper<Staff> wrapper); }2、调用示例代码： @Test void testSelfSQL() { LambdaQueryWrapper<Staff> lqw = Wrappers.lambdaQuery(Staff.class); lqw.eq(Staff::getName, "朱治龙").and(wq2 -> wq2.lt(Staff::getAge, 40).or().isNotNull(Staff::getEmail)); List<Staff> staffList = staffMapper.selectAll(lqw); staffList.forEach(System.out::println); }3、输出结果DEBUG==> Preparing: select * from staff WHERE (name = ? AND (age < ? OR email IS NOT NULL)) DEBUG==> Parameters: 朱治龙(String), 40(Integer) TRACE<== Columns: id, name, age, email, mobile, manager_id, create_time TRACE<== Row: 1714166763984199681, 朱治龙, 36, zhuzl@blsc.cn, 15084978453, 1088248166370832385, 2023-10-17 14:29:38 DEBUG<== Total: 1 Staff(id=1714166763984199681, name=朱治龙, age=36, email=zhuzl@blsc.cn, mobile=15084978453, managerId=1088248166370832385, createTime=2023-10-17T14:29:38)实现方案二：使用xml1、配置xml文件的存放路径。再application.yml中添加 xml 文件的引用路径配置mybatis-plus: mapper-locations: - classpath:/mapper/*Mapper.xml2、在resources目录下添加 mapper 目录，并新建 mapper 文件，如文件名为 StaffMapper.xml，示例内容为：<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.paratera.protect.dao.StaffMapper"> <select id="selectByXml" resultType="com.paratera.protect.entity.Staff"> select * from staff ${ew.customSqlSegment} </select> </mapper>3、Mapper 接口中添加方法，示例代码如下：package com.paratera.protect.dao; import com.baomidou.mybatisplus.core.conditions.Wrapper; import com.baomidou.mybatisplus.core.mapper.BaseMapper; import com.baomidou.mybatisplus.core.toolkit.Constants; import com.paratera.protect.entity.Staff; import org.apache.ibatis.annotations.Param; import java.util.List; /** * @author 朱治龙 * @date 2023-10-17 11:46:00 */ public interface StaffMapper extends BaseMapper<Staff> { List<Staff> selectByXml(@Param(Constants.WRAPPER)Wrapper<Staff> wrapper); }4、调用示例代码： @Test void testSelfSQL2() { LambdaQueryWrapper<Staff> lqw = Wrappers.lambdaQuery(Staff.class); lqw.eq(Staff::getName, "朱治龙").and(wq2 -> wq2.lt(Staff::getAge, 50).or().isNotNull(Staff::getEmail)); List<Staff> staffList = staffMapper.selectByXml(lqw); staffList.forEach(System.out::println); }5、输出结果DEBUG==> Preparing: select * from staff WHERE (name = ? AND (age < ? OR email IS NOT NULL)) DEBUG==> Parameters: 朱治龙(String), 50(Integer) TRACE<== Columns: id, name, age, email, mobile, manager_id, create_time TRACE<== Row: 1714166763984199681, 朱治龙, 36, zhuzl@blsc.cn, 15084978453, 1088248166370832385, 2023-10-17 14:29:38 DEBUG<== Total: 1 Staff(id=1714166763984199681, name=朱治龙, age=36, email=zhuzl@blsc.cn, mobile=15084978453, managerId=1088248166370832385, createTime=2023-10-17T14:29:38)