<!-- https://mvnrepository.com/artifact/com.github.pagehelper/pagehelper-spring-boot-starter -->
        <dependency>
            <groupId>com.github.pagehelper</groupId>
            <artifactId>pagehelper-spring-boot-starter</artifactId>
            <version>${pagehelper.version}</version>
        </dependency>

public Object getUsers(int pageNum, int pageSize) {
        PageHelper.startPage(pageNum, pageSize);
        List<UserEntity> list = userMapper.selectAllWithPage(null);
        com.github.pagehelper.Page listWithPage = (com.github.pagehelper.Page) list;
        System.out.println("listCnt:" + listWithPage.getTotal());
        return list;
    }

<select id="selectAllWithPage" parameterType="java.util.Map"
        resultType="com.my.mvc.app.dao.entity.UserEntity">
        select * from t_users
    </select>

// com.github.pagehelper.PageInterceptor#intercept
    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        try {
            Object[] args = invocation.getArgs();
            MappedStatement ms = (MappedStatement) args[0];
            Object parameter = args[1];
            RowBounds rowBounds = (RowBounds) args[2];
            ResultHandler resultHandler = (ResultHandler) args[3];
            Executor executor = (Executor) invocation.getTarget();
            CacheKey cacheKey;
            BoundSql boundSql;
            //由于邏輯關(guān)系，只會進(jìn)入一次
            if (args.length == 4) {
                //4 個(gè)參數(shù)時(shí)
                boundSql = ms.getBoundSql(parameter);
                cacheKey = executor.createCacheKey(ms, parameter, rowBounds, boundSql);
            } else {
                //6 個(gè)參數(shù)時(shí)
                cacheKey = (CacheKey) args[4];
                boundSql = (BoundSql) args[5];
            }
            checkDialectExists();
            List resultList;
            //調(diào)用方法判斷是否需要進(jìn)行分頁，如果不需要，直接返回結(jié)果
            if (!dialect.skip(ms, parameter, rowBounds)) {
                //判斷是否需要進(jìn)行 count 查詢
                if (dialect.beforeCount(ms, parameter, rowBounds)) {
                    //查詢總數(shù)
                    Long count = count(executor, ms, parameter, rowBounds, resultHandler, boundSql);
                    //處理查詢總數(shù)，返回 true 時(shí)繼續(xù)分頁查詢，false 時(shí)直接返回
                    if (!dialect.afterCount(count, parameter, rowBounds)) {
                        //當(dāng)查詢總數(shù)為 0 時(shí)，直接返回空的結(jié)果
                        return dialect.afterPage(new ArrayList(), parameter, rowBounds);
                    }
                }
                resultList = ExecutorUtil.pageQuery(dialect, executor,
                        ms, parameter, rowBounds, resultHandler, boundSql, cacheKey);
            } else {
                //rowBounds用參數(shù)值，不使用分頁插件處理時(shí)，仍然支持默認(rèn)的內(nèi)存分頁
                resultList = executor.query(ms, parameter, rowBounds, resultHandler, cacheKey, boundSql);
            }
            return dialect.afterPage(resultList, parameter, rowBounds);
        } finally {
            if(dialect != null){
                dialect.afterAll();
            }
        }
    }

/**
     * 開始分頁
     *
     * @param pageNum  頁碼
     * @param pageSize 每頁顯示數(shù)量
     * @param count    是否進(jìn)行count查詢
     */
    public static <E> Page<E> startPage(int pageNum, int pageSize, boolean count) {
        return startPage(pageNum, pageSize, count, null, null);
    }
    /**
     * 開始分頁
     *
     * @param pageNum      頁碼
     * @param pageSize     每頁顯示數(shù)量
     * @param count        是否進(jìn)行count查詢
     * @param reasonable   分頁合理化,null時(shí)用默認(rèn)配置
     * @param pageSizeZero true且pageSize=0時(shí)返回全部結(jié)果，false時(shí)分頁,null時(shí)用默認(rèn)配置
     */
    public static <E> Page<E> startPage(int pageNum, int pageSize, boolean count, Boolean reasonable, Boolean pageSizeZero) {
        Page<E> page = new Page<E>(pageNum, pageSize, count);
        page.setReasonable(reasonable);
        page.setPageSizeZero(pageSizeZero);
        //當(dāng)已經(jīng)執(zhí)行過orderBy的時(shí)候
        Page<E> oldPage = getLocalPage();
        if (oldPage != null && oldPage.isOrderByOnly()) {
            page.setOrderBy(oldPage.getOrderBy());
        }
        setLocalPage(page);
        return page;
    }
    protected static final ThreadLocal<Page> LOCAL_PAGE = new ThreadLocal<Page>();
    /**
     * 設(shè)置 Page 參數(shù)
     *
     * @param page
     */
    protected static void setLocalPage(Page page) {
        LOCAL_PAGE.set(page);
    }
    // com.github.pagehelper.PageHelper#afterAll
    @Override
    public void afterAll() {
        //這個(gè)方法即使不分頁也會被執(zhí)行，所以要判斷 null
        AbstractHelperDialect delegate = autoDialect.getDelegate();
        if (delegate != null) {
            delegate.afterAll();
            autoDialect.clearDelegate();
        }
        clearPage();
    }
    /**
     * 移除本地變量
     */
    public static void clearPage() {
        LOCAL_PAGE.remove();
    }

@RestController
@RequestMapping("/hello")
@Slf4j
public class HelloController {
    @Resource
    private UserService userService;
    // 1. 先請求該getUsers接口，將得到異常，pageNum=1, pageSize=1
    @GetMapping("getUsers")
    @ResponseBody
    public Object getUsers(int pageNum, int pageSize) {
        return userService.getUsers(pageNum, pageSize);
    }
    // 2. 多次請求該 getAllActors接口，正常情況下會得到N條全表記錄，但將會偶發(fā)地得到只有一條記錄，現(xiàn)象復(fù)現(xiàn)
    @GetMapping("getAllActors")
    @ResponseBody
    public Object getAllActors() {
        return userService.getAllActors();
    }
}
@Service
@Slf4j
public class UserService {
    @Resource
    private UserMapper userMapper;
    public Object getUsers(int pageNum, int pageSize) {
        PageHelper.startPage(pageNum, pageSize);
        // 此處強(qiáng)行拋出異常, 使以上 pagehelper 信息得以保存
        throw new RuntimeException("exception ran");
    }
    public Object getAllActors() {
        // 正常的全表查詢
        List<ActorEntity> list = userMapper.selectAllActors();
        return list;
    }
}