java中实现分页的几种常见方式总结

mysql写法：
SELECT * FROM user2
LIMIT (#{pageNum} - 1) * #{pageSize}, #{pageSize}

oracle写法：
SELECT * FROM user2
OFFSET (#{pageNum} - 1) * #{pageSize} ROWS FETCH NEXT #{pageSize} ROWS ONLY

@Mapper
public interface PageTestDao {
	
	// 查数据
	// start：从第几条开始，向后要数据
	// pageSize：一页多少条数据
    List<UserEntity> getUserInfoByParams(@Param("nameParam") String name,
                                         @Param("start") int start,
                                         @Param("pageSize") int pageSize);
	// 返回总条数
    int getCountByParams(@Param("nameParam") String name);
}

<?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.example.csdn2.page_test.dao.PageTestDao">

    <sql id="nameCondition">
        <where>
            <if test="nameParam != null and nameParam != ''">
                name like CONCAT('%', #{nameParam}, '%')
            </if>
        </where>
    </sql>

    <select id="getUserInfoByParams" resultType="com.example.csdn2.page_test.entity.UserEntity">
        SELECT * FROM user2
        <include refid="nameCondition" />
        LIMIT #{start}, #{pageSize}
    </select>

    <select id="getCountByParams" resultType="int">
        SELECT COUNT(*) FROM user2
        <include refid="nameCondition" />
    </select>
</mapper>

@Service
@RequiredArgsConstructor
public class PageTestService {

    private final PageTestDao pageTestDao;

    public PageResponse<UserEntity> getPageTest(UserRequest userRequest) {
        final List<UserEntity> userEntityList = pageTestDao.getUserInfoByParams(userRequest.getNameParam(),
                userRequest.getStart(), userRequest.getPageSize());

        final int total = pageTestDao.getCountByParams(userRequest.getNameParam());

        return new PageResponse<>(userEntityList, total);
    }
}

// 若分页的需求很多，可把分页相关的参数抽出来
@Data
public class PageRequest {

    // 第几页
    private int pageNum;

    // 每页几行数据
    private int pageSize;

	// 计算从第几行开始
	// 无论是limit、还是fetch 都是从某一行数据开始，向后取 pageSize 条数据
    public int getStart() {
        if (pageNum <= 0) {
            return 0;
        }
        return (pageNum - 1) * pageSize;
    }
}

// 入参
@EqualsAndHashCode(callSuper = true)
@Data
public class UserRequest extends PageRequest {

    // 搜索参数
    private String nameParam;
}

// 返回实体类，因为分页需要返回总条数，前端好做下标第几页
@Data
@AllArgsConstructor
public class PageResponse<T> {

    private List<T> data;

	// 总条数
    private int total;
}

@RestController
@RequiredArgsConstructor
public class PageTestController {

    private final PageTestService pageTestService;

    @PostMapping("/page-test")
    public PageResponse<UserEntity> getPageTest(@RequestBody UserRequest userRequest){
       return pageTestService.getPageTest(userRequest);
    }
}

// 从第几个下标，到第几个下标
List<E> subList(int fromIndex, int toIndex);

    public void test_ListSub() {
    	// 创建模拟数据，字符串 0-9的集合
        final List<String> list = IntStream.range(0, 10)
                .mapToObj(i -> i + "")
                .collect(Collectors.toList());
        System.out.println(list);
        // 截取从下标0到5的数据
        System.out.println(list.subList(0, 5));
        // 截取从下标3到5的数据
        System.out.println(list.subList(3, 5));
    }

  SELECT * FROM user2
  name like CONCAT('%', #{nameParam}, '%')

 public PageResponse<UserEntity> getPageTestByListSub(UserRequest userRequest) {
        final List<UserEntity> allData = pageTestDao.getUserInfoByParamsNoLimit(userRequest.getNameParam());
        // 下标开始
        final int start = userRequest.getStart();
        // 下标结束
        final int end = start + userRequest.getPageSize();
        // 截取数据
        final List<UserEntity> userEntityList = allData.subList(start, end);

        final int total = pageTestDao.getCountByParams(userRequest.getNameParam());
        return new PageResponse<>(userEntityList, total);
    }

<dependency>
        <groupId>com.github.pagehelper</groupId>
        <artifactId>pagehelper-spring-boot-starter</artifactId>
        <version>1.3.0</version>
</dependency>

  SELECT * FROM user2
  name like CONCAT('%', #{nameParam}, '%')

   public PageInfo<UserEntity> getPageTest(UserRequest userRequest) {
        // 告诉PageHelper数据要从第几页，每页多少条数据
        // 注：一定要在select查询语句之前使用该方法，否则无效
        PageHelper.startPage(userRequest.getPageNum(), userRequest.getPageSize());
        
        // 查询sql
        final List<UserEntity> userEntityList = pageTestDao.getUserInfoByParamsNotLimit(userRequest.getNameParam());

        // 返回dto，使用插件自带的PageInfo
        return new PageInfo<>(userEntityList);

		// 上述逻辑还可以简写为：
		// return PageHelper.startPage(userRequest.getPageNum(), userRequest.getPageSize())
            // .doSelectPageInfo(() -> pageTestDao.getUserInfoByParamsNotLimit(userRequest.getNameParam()));
    }

	// 当前页
    private int pageNum;
    // 每页的数量
    private int pageSize;
    // 当前页的数量
    private int size;

    // 总记录数
    private long total;
    // 总页数
    private int pages;
    // 结果集
    private List<T> list;
 
 	// 以下内容都是其自动帮生成的
 	// 对于前端来说极其友好，前端分页功能的全部参数都包含了
    // 前一页的页码
    private int prePage;
    // 下一页的页码
    private int nextPage;
    // 是否为第一页
    private boolean isFirstPage = false;
    // 是否为最后一页
    private boolean isLastPage = false;
    // 是否有前一页
    private boolean hasPreviousPage = false;
    // 是否有下一页
    private boolean hasNextPage = false;
    // 导航条上的第一页的页码
    private int navigateFirstPage;
    // 导航条上的第一页的页码
    private int navigateLastPage;