一、MyBatisPlusConfig中配置分頁插件

   /**
     * 配置分頁插件
     * @return page
     */
    @Bean
    public PaginationInterceptor paginationInterceptor(){
        PaginationInterceptor paginationInterceptor = new PaginationInterceptor();
        // 開啟 count 的 join 優化,只針對部分 left join
        paginationInterceptor.setCountSqlParser(new JsqlParserCountOptimize(true));
        return paginationInterceptor;
    }

1. 分頁實現的原理

Mybatis-plus分頁插件使用的是IPage進行分頁。IPage內部原理是基於攔截器，攔截的是方法以及方法中的參數。判斷是否是查詢操作，如果是查詢操作，才會進入分頁的處理邏輯。進入分頁邏輯處理後，攔截器會通過反射獲取該方法的參數進行判斷是否存在IPage對象的實現類。如果不存在則不進行分頁，存在則將該參數賦值給IPage對象，然後進行拼接sql的處理完成分頁操作。

二、統一結果集

1. 創建返回碼定義類

public class ResultCode {

    /**
     * 成功
     **/
    public final static int OK = 20000;
    /**
     * 失敗
     **/
    public final static int ERROR = 20001;
    /**
     * 用戶名或密碼錯誤
     **/
    public final static int LOGIN_ERROR = 20002;
    /**
     * 許可權不足
     **/
    public final static int ACCESS_ERROR = 20003;
    /**
     * 遠程調用失敗
     **/
    public final static int REMOTE_ERROR = 20004;
    /**
     * 重複操作
     **/
    public final static int REPEAT_ERROR = 20005;
}

2. 創建結果集類

@Data
@ApiModel(value = "全局統一返回結果")
public class R implements Serializable {

    public final static String OK_MSG = "請求成功";
    public final static String FAIL_MSG = "請求失敗";

    @ApiModelProperty(value = "是否成功")
    private boolean success;

    @ApiModelProperty(value = "返回碼")
    private Integer code;

    @ApiModelProperty(value = "返回消息")
    private String message;

    @ApiModelProperty(value = "返回數據")
    private Object data;

    @ApiModelProperty(value = "總條數")
    private Long total;

    @ApiModelProperty(value = "分頁信息")
    private PageInfo pageInfo;

    @Data
    public static class PageInfo {

        @ApiModelProperty("當前頁")
        protected int currentPage;
        @ApiModelProperty("頁大小")
        protected int pageSize;
        @ApiModelProperty("總記錄數")
        protected long totalCount;
        @ApiModelProperty("總頁數")
        protected long totalPage;

        public PageInfo() {
        }

        @ConstructorProperties({"currentPage", "pageSize", "totalCount", "totalPage"})
        public PageInfo(int currentPage, int pageSize, long totalCount, long totalPage) {
            this.currentPage = currentPage;
            this.pageSize = pageSize;
            this.totalCount = totalCount;
            this.totalPage = totalPage;
        }
    }

    private R(){}

    private R(int code, String msg, Object data) {
        this.code = code;
        this.message = msg;
        if (data instanceof Page<?>) {
            Page<?> page = (Page<?>) data;
            this.total = page.getTotal();
            this.data = page.getRecords();
            this.pageInfo = new PageInfo((int)page.getCurrent(), (int)page.getSize(), page.getTotal(), page.getPages());
        } else {
            this.data = data;
        }
    }

    public static R ok(){
        R r = new R();
        r.setSuccess(true);
        r.setCode(ResultCode.OK);
        r.setMessage("成功");
        return r;
    }
    public static R ok(Object data) {
        return new R(ResultCode.OK, OK_MSG, data);
    }

    public static R ok(String msg, Object data) {
        return new R(ResultCode.OK, msg, data);
    }

    public static R error(){
        R r = new R();
        r.setSuccess(false);
        r.setCode(ResultCode.ERROR);
        r.setMessage("失敗");
        return r;
    }

    public static R error(String msg) {
        return new R(ResultCode.ERROR, msg, null);
    }

    public static R error(int errorCode, String msg) {
        return new R(errorCode, msg, null);
    }


    public R message(String message){
        this.setMessage(message);
        return this;
    }

    public R code(Integer code){
        this.setCode(code);
        return this;
    }

    public R data(Object data){
        this.setData(data);
        return this;
    }

}

三、編寫分頁介面

1. 先編寫查詢類

代碼如下：

@Data
public class MemberQueryVo extends BasePageEntity{

    @ApiModelProperty(value = "用戶名")
    private String userName;
}

2. service層

先定義一個查詢分頁的介面，在實現類里做相關處理

@Service
public class MemberServiceImpl extends ServiceImpl<MemberMapper, Member> implements MemberService {

    @Override
    public IPage<Member> listMemberPage(MemberQueryVo queryVo) {
        IPage<Member> page = new Page<>(queryVo.getCurrentPage(),queryVo.getCurrentPage());
        //條件查詢
        LambdaQueryWrapper<Member> queryWrapper = new LambdaQueryWrapper<Member>();

        if (StringUtils.isNotBlank(queryVo.getUserName())) {
            queryWrapper.like(Member::getUserName, queryVo.getUserName());
        }

        return baseMapper.selectPage(page,queryWrapper);
    }
}

3. controller層

編寫分頁介面，代碼如下：

    @ApiOperation(value = "分頁用戶列表")
    @GetMapping(value = "/getPage")
    public R listPage(MemberQueryVo queryVo){
        IPage<Member> page = memberService.listMemberPage(queryVo);
        return R.ok(page);
    }