文章列表（条件分页+动态sql）2021-4-1

//controller
@GetMapping
    public Result<PageBean<Article>> list(
            Integer pageNum,
            Integer pageSize,
            @RequestParam(required = false) Integer categoryId,
            @RequestParam(required = false) String state
    ){

        PageBean<Article> pb = articleService.list(pageNum,pageSize,categoryId,state);
        return Result.success(pb);
    }


//service
//条件分页列表查询
    PageBean<Article> list(Integer pageNum, Integer pageSize, Integer categoryId, String state);


//serviceImpl
 @Override
    public PageBean<Article> list(Integer pageNum, Integer pageSize, Integer categoryId, String state) {
        //1.创建PageBean对象
        PageBean<Article> pb = new PageBean<>();
        //2.开启分页查询 PageHelper
        PageHelper.startPage(pageNum,pageSize);
        //3.调用mapper
        Map<String,Object> map = ThreadLocalUtil.get();
        Integer userId = (Integer)map.get("id");
        List<Article> as = articleMapper.list(userId,categoryId,state);
        //page中提供了方法。可以获取PageHelper分页查询后，得到记录的总条数和当前页数
        Page<Article> p = (Page<Article>) as;

        //把数据填充到PageBean对象中
        pb.setTotal(p.getTotal());
        pb.setItems(p.getResult());
        return pb;
    }

//mapper
List<Article> list(Integer userId, Integer categoryId, String state);

//！！！实体类
package com.di.bigevent.pojo;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.util.List;

//分页返回结果对象
@Data
@NoArgsConstructor
@AllArgsConstructor
public class PageBean <T>{
    private Long total;//总条数
    private List<T> items;//当前页数据集合
}

在resources里，根据原mapper包的文件路径，创建mapper包，然后再创建ArticleMapper.xml

<?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.di.bigevent.mapper.ArticleMapper">
    <!--动态sql-->
    <select id = "list" resultType="com.di.bigevent.pojo.Article">
            select * from article
            <where>
                <if test="categoryId!=null">
                   category_id = #{categoryId}
                </if>
                <if test="state!=null">
                   and state = #{state}
                </if>
                and create_user = #{userId}
            </where>
    </select>
</mapper>

#要用到
<!--PageHelper坐标-->
        <dependency>
            <groupId>com.github.pagehelper</groupId>
            <artifactId>pagehelper-spring-boot-starter</artifactId>
            <version>1.4.6</version>
        </dependency>