MybatisPlus的分页插件

PaginationInnerInterceptor

此插件是核心插件,目前代理了 Executor#query 和 Executor#update 和 StatementHandler#prepare 方法。

在SpringBoot环境中配置方式如下：

/*** @author giserDev* @description 配置分页插件、方言、mapper包扫描等* @date 2023-12-13 23:23:35*/
@Configuration
@MapperScan("com.giser.mybatisplus.mapper")
public class MyBatisPlusConfig {@Beanpublic MybatisPlusInterceptor mybatisPlusInterceptor(){MybatisPlusInterceptor mybatisPlusInterceptor = new MybatisPlusInterceptor();mybatisPlusInterceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));return mybatisPlusInterceptor;}}

测试分页功能：

import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.giser.mybatisplus.mapper.UserMapper;
import com.giser.mybatisplus.pojo.User;
import lombok.extern.slf4j.Slf4j;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;/*** @author giserDev* @description* @date 2023-12-13 23:28:43*/
@Slf4j
@SpringBootTest
public class MyBatisPlusPluginsTest {@Autowiredprivate UserMapper userMapper;@Testpublic void testMyBatisPlusPage(){Page<User> page = new Page<>(1,3);userMapper.selectPage(page, null);log.info("分页查询结果为：{}", page);}}

如何自定义分页？

# mybatis-plus配置
mybatis-plus:configuration:# 引入日志log-impl: org.apache.ibatis.logging.stdout.StdOutImplglobal-config:db-config:# 配置MybatisPlus操作的表的前缀table-prefix: t_# 配置MybatisPlus的主键生成策略id-type: assign_id# 指定类型别名type-aliases-package: com.giser.mybatisplus.pojo

在Mapper接口中定义分页方法：

@Repository
public interface UserMapper extends BaseMapper<User> {/*** 利用MybatisPlus的分页功能* @param page 分页对象，必须在第一个参数位置，传递参数 Page 即自动分页* @param userName 查询条件* @return 结果*/Page<User> selectPageByName(@Param("page") Page<User> page, @Param("userName") String userName);}

在Mapper.xml文件中实现分页语句：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.giser.mybatisplus.mapper.UserMapper"><select id="selectPageByName" resultType="User">select * from user where user_name = #{userName}</select></mapper>

分页测试：

import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.giser.mybatisplus.mapper.UserMapper;
import com.giser.mybatisplus.pojo.User;
import lombok.extern.slf4j.Slf4j;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;@Slf4j
@SpringBootTest
public class MyBatisPlusPluginsTest {@Autowiredprivate UserMapper userMapper;/*** ==>  Preparing: SELECT COUNT(*) AS total FROM user WHERE is_deleted = 0* ==> Parameters:* <==    Columns: total* <==        Row: 25* <==      Total: 1* ==>  Preparing: SELECT id,user_name AS name,age,email,is_deleted FROM user WHERE is_deleted=0 LIMIT ?* ==> Parameters: 3(Long)* <==    Columns: id, name, age, email, is_deleted* <==        Row: 1, Jone, 18, test1@baomidou.com, 0* <==        Row: 2, 窃听风云, 23, giserDev@163.com, 0* <==        Row: 3, Tom, 28, test3@baomidou.com, 0* <==      Total: 3* Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@3a109ff7]* 分页查询结果为：com.baomidou.mybatisplus.extension.plugins.pagination.Page@5ee77baf* 分页查询记录结果为：[User(id=1, name=Jone, age=18, email=test1@baomidou.com, isDeleted=0), User(id=2, name=窃听风云, age=23, email=giserDev@163.com, isDeleted=0), User(id=3, name=Tom, age=28, email=test3@baomidou.com, isDeleted=0)]* 分页查询记录条数为：25* 分页查询当前页码为：1* 分页查询每页大小为：3*/@Testpublic void testMyBatisPlusPage(){Page<User> page = new Page<>(1,3);userMapper.selectPage(page, null);log.info("分页查询结果为：{}", page);log.info("分页查询记录结果为：{}", page.getRecords());log.info("分页查询记录条数为：{}", page.getTotal());log.info("分页查询当前页码为：{}", page.getCurrent());log.info("分页查询每页大小为：{}", page.getSize());}/*** ==>  Preparing: SELECT COUNT(*) AS total FROM user WHERE user_name = ?* ==> Parameters: 李雷(String)* <==    Columns: total* <==        Row: 1* <==      Total: 1* ==>  Preparing: select * from user where user_name = ? LIMIT ?* ==> Parameters: 李雷(String), 3(Long)* <==    Columns: id, user_name, age, email, is_deleted* <==        Row: 1734579107187970050, 李雷, 12, null, 1* <==      Total: 1* Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@a316f6b]* 分页查询结果为：com.baomidou.mybatisplus.extension.plugins.pagination.Page@48368a08* 分页查询记录结果为：[User(id=1734579107187970050, name=null, age=12, email=null, isDeleted=1)]* 分页查询记录条数为：1* 分页查询当前页码为：1* 分页查询每页大小为：3*/@Testvoid testAutoPage(){Page<User> page = new Page<>(1,3);userMapper.selectPageByName(page, "李雷");log.info("分页查询结果为：{}", page);log.info("分页查询记录结果为：{}", page.getRecords());log.info("分页查询记录条数为：{}", page.getTotal());log.info("分页查询当前页码为：{}", page.getCurrent());log.info("分页查询每页大小为：{}", page.getSize());}}

问题：分页参数处理原理

拦截执行的语句
org.apache.ibatis.plugin.Plugin#invoke

if (methods != null && methods.contains(method)) {
return interceptor.intercept(new Invocation(target, method, args));
}

com.baomidou.mybatisplus.extension.plugins.MybatisPlusInterceptor#intercept

    @Overridepublic Object intercept(Invocation invocation) throws Throwable {// ...for (InnerInterceptor query : interceptors) {// com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor#willDoQuery// willDoQuery()，先判断总条数，决定是否执行sql语句if (!query.willDoQuery(executor, ms, parameter, rowBounds, resultHandler, boundSql)) {return Collections.emptyList();}// beforeQuery()，处理排序、分页方言query.beforeQuery(executor, ms, parameter, rowBounds, resultHandler, boundSql);
}// ...

    @Overridepublic boolean willDoQuery(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {// 查找分页参数IPage<?> page = ParameterUtils.findPage(parameter).orElse(null);if (page == null || page.getSize() < 0 || !page.searchCount()) {return true;}// ...// 组装统计语句，判断总条数long total = 0;if (CollectionUtils.isNotEmpty(result)) {// 个别数据库 count 没数据不会返回 0Object o = result.get(0);if (o != null) {total = Long.parseLong(o.toString());}}page.setTotal(total);// protected boolean continuePage(IPage<?> page)// 返回是否继续执行后面的查询语句，执行则返回true,否则返回falsereturn continuePage(page);}

willDoQuery()方法中包含查询分页参数的逻辑，如下：

/*** 查找分页参数** @param parameterObject 参数对象* @return 分页参数*/
public static Optional<IPage> findPage(Object parameterObject) {if (parameterObject != null) {// 若参数类型为Map，则从map中查找类型为IPage的参数，作为分页参数if (parameterObject instanceof Map) {Map<?, ?> parameterMap = (Map<?, ?>) parameterObject;for (Map.Entry entry : parameterMap.entrySet()) {if (entry.getValue() != null && entry.getValue() instanceof IPage) {return Optional.of((IPage) entry.getValue());}}} else if (parameterObject instanceof IPage) {// 若参数类型为IPage，则直接返回，作为分页参数return Optional.of((IPage) parameterObject);}}return Optional.empty();
}

com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor#beforeQuery

@Overridepublic void beforeQuery(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {IPage<?> page = ParameterUtils.findPage(parameter).orElse(null);if (null == page) {return;}// 处理 orderBy 拼接boolean addOrdered = false;String buildSql = boundSql.getSql();List<OrderItem> orders = page.orders();if (CollectionUtils.isNotEmpty(orders)) {addOrdered = true;buildSql = this.concatOrderBy(buildSql, orders);}// size 小于 0 且不限制返回值则不构造分页sqlLong _limit = page.maxLimit() != null ? page.maxLimit() : maxLimit;if (page.getSize() < 0 && null == _limit) {if (addOrdered) {PluginUtils.mpBoundSql(boundSql).sql(buildSql);}return;}handlerLimit(page, _limit);// 查找方言，在配置分页插件时，设置了DbType，此时可确定方言，如此时返回的是com.baomidou.mybatisplus.extension.plugins.pagination.dialects.MySqlDialectIDialect dialect = findIDialect(executor);final Configuration configuration = ms.getConfiguration();// 构造分页语句！！！com.baomidou.mybatisplus.extension.plugins.pagination.dialects.IDialect#buildPaginationSql// 此时dialect为MySqlDialect，会调用com.baomidou.mybatisplus.extension.plugins.pagination.dialects.MySqlDialect#buildPaginationSql来构造sqlDialectModel model = dialect.buildPaginationSql(buildSql, page.offset(), page.getSize());// ...// 此处绑定执行的sql语句model.getDialectSql()mpBoundSql.sql(model.getDialectSql());mpBoundSql.parameterMappings(mappings);}

com.baomidou.mybatisplus.extension.plugins.pagination.dialects.MySqlDialect#buildPaginationSql

public class MySqlDialect implements IDialect {@Overridepublic DialectModel buildPaginationSql(String originalSql, long offset, long limit) {StringBuilder sql = new StringBuilder(originalSql).append(" LIMIT ").append(FIRST_MARK);if (offset != 0L) {sql.append(StringPool.COMMA).append(SECOND_MARK);return new DialectModel(sql.toString(), offset, limit).setConsumerChain();} else {return new DialectModel(sql.toString(), limit).setConsumer(true);}}
}