Mybatis-plus分页返回统一结果集

1.分页起作用，需要配置拦截器

@Configuration
public class MybatisPlusConfig {
    /**
     * 新的分页插件,一缓和二缓遵循mybatis的规则,需要设置 MybatisConfiguration#useDeprecatedExecutor = false 避免缓存出现问题(该属性会在旧插件移除后一同移除)
     */
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor() {
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
        return interceptor;
    }

2.分页的原理

Mybatis-plus分页插件使用的是IPage进行分页。IPage内部原理是基于拦截器，拦截的是方法以及方法中的参数。【判断是否是查询操作，如果是查询操作，才会进入分页的处理逻辑】。 进入分页逻辑处理后，拦截器会通过反射获取该方法的参数进行判断是否存在IPage对象的实现类。如果不存在则不进行分页，存在则将该参数赋值给IPage对象，（上述已说IPage分页，故参数给IPage对象）然后进行拼接sql的处理完成分页操作。

3.统一结果集 

3.1返回码定义类  提供两种任选一种

常量类模式

public class ResultCode {
    /**成功 **/
    public final static int OK = 20000;
    /** 失败 **/
    public final static int ERROR = 20001;
    /**用户名或密码错误 **/
    public final static int LOGIN_ERROR = 20002;
    /** 权限不足**/
    public final static int ACCESS_ERROR = 20003;
    /** 远程调用失败**/
    public final static int REMOTE_ERROR = 20004;
    /** 重复操作**/
    public final static int REPEAT_ERROR = 20005;
}

枚举类模式

public enum ResponseCodeEnum {
    REQUEST_OK(200, "请求成功！"),
    OPERATE_FAIL(101, "操作失败"),
    BAD_REQUEST(400, "错误请求"),
    ERROR(500, "系统异常"),
    UNAUTHORIZED(401, "未授权"),
    FORBIDDEN(403, "访问受限，授权过期"),
    NOT_FOUND(404, "资源，服务未找到"),
    NO_USER_LOGIN(1000, "用户没有登录或登录超时失效"),
    AUTHORITY_NOT_ALLOW(1002, "权限不匹配"),
    PARAM_ENUM_TRANS_EXP(2000, "传入的参数无法找到系统对应的配置值"),
    SERIOUS_PARAM_EMPTY(2001, "必输参数为空"),
    PARAM_IS_INVALID(2002, "参数无效"),
    SYSTEM_ERROR(3001, "系统异常，请稍后重试"),
    GLOBAL_EXCEPTION(6666, "抱歉，系统开小差了");

    /** 编码 */
    private Integer code;

    private String message;

    ResponseCodeEnum(Integer code, String message) {
        this.code = code;
        this.message = message;
    }

3.2结果集类  含有处理分页+不含处理分页（返回结果直接放入data中）

@Data
@ApiModel(value = "全局统一返回结果")
public class R implements Serializable {
    public final static String OK_MSG = "请求成功";
    public final static String FAIL_MSG = "请求失败";
    @ApiModelProperty(value = "是否成功")
    private boolean success;
    @ApiModelProperty(value = "返回码")
    private Integer code;
    @ApiModelProperty(value = "返回消息")
    private String message;
    @ApiModelProperty(value = "返回数据")
    private Object data;
    @ApiModelProperty(value = "总条数")
    private Long total;
    @ApiModelProperty(value = "分页信息")
    private PageInfo pageInfo;
    @Data
    public static class PageInfo {

        @ApiModelProperty("当前页")
        protected int currentPage;
        @ApiModelProperty("页大小")
        protected int pageSize;
        @ApiModelProperty("总记录数")
        protected long totalCount;
        @ApiModelProperty("总页数")
        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;
//代码重要点 此处区分分页结果或是 普通结果
        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("失败");
        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;
    }

}

public class ResponseResult {
    // 结果状态码
    private Integer code;
    // 响应信息
    private String message;
    // 响应数据
    private T data;
//方法名 ok可改为success 看个人习惯
    public static  ResponseResult ok(T data) {
        return new ResponseResult<>(codeEnum.REQUEST_OK.getCode(), codeEnum.REQUEST_OK.getMessage(), data);
    }

    public static  ResponseResult fail(T data, Integer code, String msg) {
        return new ResponseResult<>(code, msg, data);
    }

    public static  ResponseResult fail(T data, codeEnum e) {
        return new ResponseResult<>(e.getCode(), e.getMessage(), data);
    }
    public static  ResponseResult fail(codeEnum e) {
        return new ResponseResult<>(e.getCode(), e.getMessage(), null);
    }