<!-- Mybatis-Plus -->
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.4.3.4</version>
</dependency>
<!-- 分頁 -->
<dependency>
    <groupId>com.github.pagehelper</groupId>
    <artifactId>pagehelper-spring-boot-starter</artifactId>
    <version>1.4.0</version>
</dependency>
<!-- AOP -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-aop</artifactId>
    <version>2.5.5</version>
</dependency>

添加公共返回實體類

需要兩種實體類，一種是不分頁直接返回數(shù)據的，另一種是分頁返回數(shù)據和總數(shù)據條數(shù)的

普通實體類 AjaxResult

@Data
@NoArgsConstructor
@AllArgsConstructor
public class AjaxResult<T> {

    public static final int CODE_SUCCESS = 200;
    public static final int CODE_UNAUTHORIZED = 401;
    public static final int CODE_FORBIDDEN = 403;
    public static final int CODE_ERROR = 500;

    public static final String MSG_SUCCESS = "操作成功";
    public static final String MSG_FAILED = "操作失敗";
    public static final String MSG_NOT_PERMISSION = "用戶權限不足";
    public static final String MSG_UNAUTHORIZED = "用戶未登錄或身份已過期";

    private int code;
    private String msg;
    private T data;

    public static <T> AjaxResult success(int code, T data) {
        return new AjaxResult(code, MSG_SUCCESS, data);
    }

    public static <T> AjaxResult success(T data) {
        return success(CODE_SUCCESS, data);
    }

    public static AjaxResult success() {
        return success(CODE_SUCCESS, null);
    }

    public static AjaxResult error(int code, String msg) {
        return new AjaxResult(code, msg, null);
    }

    public static AjaxResult error(String msg) {
        return error(CODE_ERROR, msg);
    }

    public static AjaxResult error() {
        return new AjaxResult(CODE_ERROR, MSG_FAILED, null);
    }

}

分頁實體類 PageResult

繼承AjaxResult，額外添加total、pageNo和pageSize等字段

@Data
public class PageResult extends AjaxResult {

    private long total;
    private long pageNo;
    private long pageSize;

    public PageResult() {
        this.setCode(CODE_SUCCESS);
        this.setMsg(MSG_SUCCESS);
    }

    public PageResult(AjaxResult ajaxResult) {
        this();
        if (Objects.nonNull(ajaxResult)) {
            setCode(ajaxResult.getCode());
            setMsg(ajaxResult.getMsg());
        }
    }
}

注解處理

分頁注解 Pagination

創(chuàng)建一個用于分頁的注解Pagination

其實這里的pageNo和pageSize沒什么需求的話可以去掉的

/**
 * 分頁注解
 */
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Pagination {

    // 第幾頁的請求參數(shù)名稱 通過獲取參數(shù)名稱獲取真正的pageNo
    String pageNo() default "pageNo";
    // 分頁大小的請求參數(shù)名稱
    String pageSize() default "pageSize";

}

使用AOP進行分頁

創(chuàng)建一個類用于處理分頁注解，切入點要根據自己注解進行修改

@Aspect
@Component
@Slf4j
public class PaginationAspect {

    /**
     * 定義切入點
     */
    @Pointcut("@annotation(cn.montaro.social.aspect.annotation.Pagination)")
    public void access() {

    }

    @SneakyThrows
    @Around("access()")
    public Object around(ProceedingJoinPoint joinPoint) {
        Object[] args = joinPoint.getArgs();
        Pagination pagination = getPaginationAnnotation(joinPoint);
        startPage(pagination.pageNo(), pagination.pageSize());
        // 調用原本方法的內容并獲取返回值
        Object result = joinPoint.proceed(args);
        // 返回的數(shù)據類型要保證和注解方法上的一致
        return pageResult(result);
    }

    /**
     * 獲取Pagination注解
     *
     * @param joinPoint
     * @return
     */
    public Pagination getPaginationAnnotation(ProceedingJoinPoint joinPoint) {
        MethodSignature methodSignature = (MethodSignature) joinPoint.getSignature();
        Method method = methodSignature.getMethod();
        Pagination pagination = method.getAnnotation(Pagination.class);
        return pagination;
    }

    /**
     * 開始分頁
     */
    private void startPage(String pageNoParameterName, String pageSizeParameterName) {
        // 獲取pageNo和pageSize
        int pageNo = ServletUtils.getParameterToInt(pageNoParameterName, 1);
        int pageSize = ServletUtils.getParameterToInt(pageSizeParameterName, 10);
        PageHelper.startPage(pageNo, pageSize);
    }

    /**
     * 對分頁結果進行包裝 如果分頁成功則會返回PageResult
     *
     * @param result
     */
    private Object pageResult(Object result) {
        /**
         * 如果分頁成功，則查詢返回的結應該是一個Page {@link com.github.pagehelper.Page}
         * 進行一次強制轉換就能獲取到 total、pageNo、pageSize 這些字段
         */
        PageInfo pageInfo = null;
        AjaxResult ajaxResult = null;
        // 列表數(shù)據 如果方法返回Page則直接使用 如果是AjaxResult則getData再封裝
        Object list = null;
        if (result instanceof Page) {
            list = result;
            Page page = (Page) result;
            pageInfo = new PageInfo(page);
        } else if (result instanceof AjaxResult) {
            ajaxResult = (AjaxResult) result;
            Object data = ajaxResult.getData();
            if (data instanceof List) {
                list = data;
                pageInfo = new PageInfo((List) data);
            }
        }
        if (pageInfo != null) {
            PageResult pageResult = new PageResult(ajaxResult);
            pageResult.setData(list);
            pageResult.setPageNo(pageInfo.getPageNum());
            pageResult.setPageSize(pageInfo.getPageSize());
            pageResult.setTotal(pageInfo.getTotal());

            return pageResult;
        }
        return result;
    }
}

還有注解中使用到的ServletUtils

public class ServletUtils {

    public static HttpServletRequest getRequest() {
        ServletRequestAttributes requestAttributes = getRequestAttributes();
        return requestAttributes.getRequest();
    }

    public static ServletRequestAttributes getRequestAttributes() {
        RequestAttributes requestAttributes = RequestContextHolder.getRequestAttributes();
        return (ServletRequestAttributes) requestAttributes;
    }

    public static Integer getParameterToInt(String parameterName, Integer defaultValue) {
        HttpServletRequest request = getRequest();
        String strValue = request.getParameter(parameterName);
        Integer intValue = Convert.toInt(strValue, defaultValue);
        return intValue;
    }

    public static Integer getParameterToInt(String parameterName) {
        return getParameterToInt(parameterName, null);
    }

}

使用注解

為了避免跑題，此處就省略mybatis-plus的使用了。

需要分頁就加上@Pagination注解就行了，不需要就注釋掉，代碼完全不需要修改

分頁的時候傳入pageNo和pageSize參數(shù)就可以了，如果參數(shù)名需要更改，就修改@Pagination就可以了

編寫Controller類

@RestController
@RequestMapping("/user")
public class UserController {

    @Autowired
    private IUserService userService;

    /**
     * 列出所有用戶
     * @return
     */
    @Pagination
    @GetMapping("/list")
    public AjaxResult list(UserQueryReq query) {
        List<User> userList = userService.selectUserListByQuery(query);
        return AjaxResult.success(userList);
    }

}