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

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

@Mapper
public interface PageTestDao {
	
	// 查數(shù)據(jù)
	// start：從第幾條開始，向后要數(shù)據(jù)
	// pageSize：一頁多少條數(shù)據(jù)
    List<UserEntity> getUserInfoByParams(@Param("nameParam") String name,
                                         @Param("start") int start,
                                         @Param("pageSize") int pageSize);
	// 返回總條數(shù)
    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);
    }
}

// 若分頁的需求很多，可把分頁相關的參數(shù)抽出來
@Data
public class PageRequest {

    // 第幾頁
    private int pageNum;

    // 每頁幾行數(shù)據(jù)
    private int pageSize;

	// 計算從第幾行開始
	// 無論是limit、還是fetch 都是從某一行數(shù)據(jù)開始，向后取 pageSize 條數(shù)據(jù)
    public int getStart() {
        if (pageNum <= 0) {
            return 0;
        }
        return (pageNum - 1) * pageSize;
    }
}

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

    // 搜索參數(shù)
    private String nameParam;
}

// 返回實體類，因為分頁需要返回總條數(shù)，前端好做下標第幾頁
@Data
@AllArgsConstructor
public class PageResponse<T> {

    private List<T> data;

	// 總條數(shù)
    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);
    }
}

// 從第幾個下標，到第幾個下標
List<E> subList(int fromIndex, int toIndex);

    public void test_ListSub() {
    	// 創(chuàng)建模擬數(shù)據(jù)，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);
        // 截取從下標0到5的數(shù)據(jù)
        System.out.println(list.subList(0, 5));
        // 截取從下標3到5的數(shù)據(jù)
        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());
        // 下標開始
        final int start = userRequest.getStart();
        // 下標結束
        final int end = start + userRequest.getPageSize();
        // 截取數(shù)據(jù)
        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) {
        // 告訴PageHelper數(shù)據(jù)要從第幾頁，每頁多少條數(shù)據(jù)
        // 注：一定要在select查詢語句之前使用該方法，否則無效
        PageHelper.startPage(userRequest.getPageNum(), userRequest.getPageSize());
        
        // 查詢sql
        final List<UserEntity> userEntityList = pageTestDao.getUserInfoByParamsNotLimit(userRequest.getNameParam());

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

		// 上述邏輯還可以簡寫為：
		// return PageHelper.startPage(userRequest.getPageNum(), userRequest.getPageSize())
            // .doSelectPageInfo(() -> pageTestDao.getUserInfoByParamsNotLimit(userRequest.getNameParam()));
    }

	// 當前頁
    private int pageNum;
    // 每頁的數(shù)量
    private int pageSize;
    // 當前頁的數(shù)量
    private int size;

    // 總記錄數(shù)
    private long total;
    // 總頁數(shù)
    private int pages;
    // 結果集
    private List<T> list;
 
 	// 以下內容都是其自動幫生成的
 	// 對于前端來說極其友好，前端分頁功能的全部參數(shù)都包含了
    // 前一頁的頁碼
    private int prePage;
    // 下一頁的頁碼
    private int nextPage;
    // 是否為第一頁
    private boolean isFirstPage = false;
    // 是否為最后一頁
    private boolean isLastPage = false;
    // 是否有前一頁
    private boolean hasPreviousPage = false;
    // 是否有下一頁
    private boolean hasNextPage = false;
    // 導航條上的第一頁的頁碼
    private int navigateFirstPage;
    // 導航條上的第一頁的頁碼
    private int navigateLastPage;