public interface BaseMapper<T> extends Mapper<T> {
    <P extends IPage<T>> P selectPage(P page, @Param("ew") Wrapper<T> queryWrapper);

    <P extends IPage<Map<String, Object>>> P selectMapsPage(P page, @Param("ew") Wrapper<T> queryWrapper);
          ……
    }

    @Test
    public void testPage() {
        System.out.println("----- selectPage method test ------");
        //分頁(yè)參數(shù)
        Page<User> page = Page.of(1,10);

        //queryWrapper組裝查詢where條件
        LambdaQueryWrapper<User> queryWrapper = new LambdaQueryWrapper<>();
        queryWrapper.eq(User::getAge,13);
        userMapper.selectPage(page,queryWrapper);
        page.getRecords().forEach(System.out::println);
    }

@Configuration
public class MybatisPlusConfig {
    /**
     * 新增分頁(yè)攔截器，并設(shè)置數(shù)據(jù)庫(kù)類型為mysql
     */
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor() {
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
        return interceptor;
    }
}

//select查詢請(qǐng)求的前置方法
public void beforeQuery(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
    //根據(jù)請(qǐng)求參數(shù)來判斷是否采用分頁(yè)查詢，參數(shù)中含有IPage類型的參數(shù)，則執(zhí)行分頁(yè)
    IPage<?> page = (IPage)ParameterUtils.findPage(parameter).orElse((Object)null);
    if (null != page) {
        boolean addOrdered = false;
        String buildSql = boundSql.getSql();
        List<OrderItem> orders = page.orders();
        if (CollectionUtils.isNotEmpty(orders)) {
            addOrdered = true;
            buildSql = this.concatOrderBy(buildSql, orders);
        }

        //根據(jù)page參數(shù)，組裝分頁(yè)查詢sql
        Long _limit = page.maxLimit() != null ? page.maxLimit() : this.maxLimit;
        if (page.getSize() < 0L && null == _limit) {
            if (addOrdered) {
                PluginUtils.mpBoundSql(boundSql).sql(buildSql);
            }

        } else {
            this.handlerLimit(page, _limit);
            IDialect dialect = this.findIDialect(executor);
            Configuration configuration = ms.getConfiguration();
            DialectModel model = dialect.buildPaginationSql(buildSql, page.offset(), page.getSize());
            MPBoundSql mpBoundSql = PluginUtils.mpBoundSql(boundSql);
            List<ParameterMapping> mappings = mpBoundSql.parameterMappings();
            Map<String, Object> additionalParameter = mpBoundSql.additionalParameters();
            model.consumers(mappings, configuration, additionalParameter);
            mpBoundSql.sql(model.getDialectSql());
            mpBoundSql.parameterMappings(mappings);
        }
    }
}

//發(fā)現(xiàn)參數(shù)中的IPage對(duì)象
public static Optional<IPage> findPage(Object parameterObject) {
    if (parameterObject != null) {
        //如果是多個(gè)參數(shù)，會(huì)轉(zhuǎn)為map對(duì)象;只要任意一個(gè)value中包含IPage類型的對(duì)象，返回IPage對(duì)象
        if (parameterObject instanceof Map) {
            Map<?, ?> parameterMap = (Map)parameterObject;
            Iterator var2 = parameterMap.entrySet().iterator();

            while(var2.hasNext()) {
                Entry entry = (Entry)var2.next();
                if (entry.getValue() != null && entry.getValue() instanceof IPage) {
                    return Optional.of((IPage)entry.getValue());
                }
            }
            
         //如果只有單個(gè)參數(shù)，且類型為IPage，則返回IPage對(duì)象
        } else if (parameterObject instanceof IPage) {
            return Optional.of((IPage)parameterObject);
        }
    }

    return Optional.empty();
}

  <dependency>
       <groupId>com.baomidou</groupId>
       <artifactId>mybatis-plus-boot-starter</artifactId>
       <version>3.5.2</version>
   </dependency>

public interface UserMapper extends CommonMapper<User> {

    /**
     * 不分頁(yè)dto條件查詢
     * @param userDto
     * @return
     */
    List<User> selectByDto(@Param("userDto") UserDto userDto);


    /**
     * 支持分頁(yè)的dto條件查詢
     * @param page
     * @param userDto
     * @return
     */
    IPage<User> selectPageByDto(IPage<User> page,@Param("userDto") UserDto userDto);
}

 <sql id="selectByDtoSql">
        select  * from user t
        <where>
            <if test="userDto.name != null and userDto.name != '' ">
                AND t.name like CONCAT('%',#{userDto.name},'%')
            </if>
            <if test="userDto.age != null">
                AND t.age = #{userDto.age}
            </if>
        </where>
    </sql>

    <select id="selectByDto" resultType="com.laowan.mybatis_plus.model.User">
       <include refid="selectByDtoSql"/>
    </select>

    <select id="selectPageByDto" resultType="com.laowan.mybatis_plus.model.User">
        <include refid="selectByDtoSql"/>
    </select>

@Test
  public void testSelectPageByDto() {
       System.out.println("----- SelectPageByDto method test ------");
       //分頁(yè)參數(shù)Page，也作為查詢結(jié)果接受體
       Page<User> page = Page.of(1,10);
       //查詢參數(shù)
       UserDto userDto = new UserDto();
       userDto.setName("test");
       
       userMapper.selectPageByDto(page,userDto);

       page.getRecords().forEach(System.out::println);
   }

    @Test
    public void testSelectPageByDto() {
        System.out.println("----- SelectPageByDto method test ------");
        //查詢參數(shù)
        UserDto userDto = new UserDto();
        userDto.setName("test");

        //PageDTO.of(1,10)對(duì)象只作為查詢參數(shù)，
        IPage<User> page = userMapper.selectPageByDto(PageDTO.of(1,10),userDto);
        
        page.getRecords().forEach(System.out::println);
    }

public IPage<UserVO> list(PageRequest request) {
  IPage<UserDO> page = new Page(request.getPageNum(), request.pageSize());
  LambdaQueryWrapper<UserDO> qw = Wrappers.lambdaQuery();
  page  = userMapper.selectPage(page, qw);
  return page.convert(u->{ 
    UserVO v = new UserVO();
    BeanUtils.copyProperties(u, v);
    return v;
  });
}

<dependency>
    <groupId>com.github.pagehelper</groupId>
    <artifactId>pagehelper</artifactId>
    <version>最新版本</version>
</dependency>

//獲取第1頁(yè)，10條內(nèi)容，默認(rèn)查詢總數(shù)count
PageHelper.startPage(1, 10);
List<Country> list = countryMapper.selectAll();
//用PageInfo對(duì)結(jié)果進(jìn)行包裝
PageInfo page = new PageInfo(list);