Mybatis-Plus配置扫描mapper及分页插件

配置类

package com.xuecheng.content.config;

import com.baomidou.mybatisplus.annotation.DbType;
import com.baomidou.mybatisplus.autoconfigure.ConfigurationCustomizer;
import com.baomidou.mybatisplus.extension.plugins.MybatisPlusInterceptor;
import com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * 

 *        Mybatis-Plus 配置
 * 
 */
@Configuration
@MapperScan("com.xuecheng.content.mapper")
public class MybatisPlusConfig {
   /**
    * 定义分页拦截器
    */
   @Bean
   public MybatisPlusInterceptor mybatisPlusInterceptor() {
      MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
      interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
      return interceptor;
   }
   

}

分页插件的原理：
首先分页参数放到ThreadLocal中，拦截执行的sql，根据数据库类型添加对应的分页语句重写sql，例如：(select * from table where a) 转换为 (select count(*) from table where a)和(select * from table where a limit ,)
计算出了total总条数、pageNum当前第几页、pageSize每页大小和当前页的数据，是否为首页，是否为尾页，总页数等。

使用

准备PageParams

package com.xuecheng.base.model;

import lombok.Data;
import lombok.ToString;

@Data
@ToString
public class PageParams {
    //当前页码
    private Long pageNo = 1L;
    //每页记录数默认值
    private Long pageSize =10L;
    public PageParams(){

    }
    public PageParams(long pageNo,long pageSize){
        this.pageNo = pageNo;
        this.pageSize = pageSize;
    }
}

准备PageResult

package com.xuecheng.base.model;

import lombok.Data;
import lombok.ToString;

import java.io.Serializable;
import java.util.List;
@Data
@ToString
public class PageResult<T> implements Serializable {

   // 数据列表
   private List<T> items;

   //总记录数
   private long counts;

   //当前页码
   private long page;

   //每页记录数
   private long pageSize;

   public PageResult(List<T> items, long counts, long page, long pageSize) {
       this.items = items;
       this.counts = counts;
       this.page = page;
       this.pageSize = pageSize;
   }
}

使用

//分页参数
PageParams pageParams = new PageParams();
pageParams.setPageNo(1L);//页码
pageParams.setPageSize(3L);//每页记录数
Page<CourseBase> page = new Page<>(pageParams.getPageNo(), pageParams.getPageSize());
//分页查询E page 分页参数, @Param("ew") Wrapper queryWrapper 查询条件
Page<CourseBase> pageResult = courseBaseMapper.selectPage(page, queryWrapper);
//数据
List<CourseBase> items = pageResult.getRecords();
//总记录数
long total = pageResult.getTotal();
//准备返回数据 List items, long counts, long page, long pageSize
PageResult<CourseBase> courseBasePageResult = new PageResult<>(items, total, pageParams.getPageNo(), pageParams.getPageSize());