SpringBoot 把PageHelper分页信息返回给前端

第1步：定义线程容器收纳HttpHeaders和HttpStatus

import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;


public class ResponseUtils {
    private static ThreadLocal<HttpHeaders> ThreadLocalHeaders = new InheritableThreadLocal<>();
    private static ThreadLocal<HttpStatus> ThreadLocalStatus = new InheritableThreadLocal<>();

    public static void addHeaders(String key, String value) {
        if (ThreadLocalHeaders.get() == null) {
            ThreadLocalHeaders.set(new HttpHeaders());
        }
        ThreadLocalHeaders.get().add(key, value);
    }

    public static void setResponseCode(HttpStatus httpStatus) {
        ThreadLocalStatus.set(httpStatus);
    }

    public static HttpHeaders getHeaders() {
        return ThreadLocalHeaders.get();
    }

    public static HttpStatus getResponseCode() {
        return ThreadLocalStatus.get();
    }

    public static void clear() {
        if (ThreadLocalHeaders.get() != null) {
            ThreadLocalHeaders.remove();
        }
        if (ThreadLocalStatus.get() != null) {
            ThreadLocalStatus.remove();
        }
    }
}

第2步：分页信息 转储到 线程容器 方法的封装

import com.github.pagehelper.PageInfo;
import com.zhangziwa.practisesvr.utils.response.ResponseUtils;

public class PageHeaderUtils {
    private static final String PAGE_NUM = "page_num"; // 当前第几页
    private static final String PAGE_SIZE = "page_size"; // 每页显示的条数
    private static final String PREV_PAGE = "prev_page"; // 上一页页码
    private static final String NEXT_PAGE = "next_page"; // 下一页页码
    private static final String TOTAL_COUNT = "total_count"; // 总条数
    private static final String TOTAL_PAGE = "total_page"; // 总页数

    public static <E> void setPageHeader(PageInfo<E> page) {
        if (page == null) {
            return;
        }
        ResponseUtils.addHeaders(PAGE_NUM, String.valueOf(page.getPageNum()));
        ResponseUtils.addHeaders(PAGE_SIZE, String.valueOf(page.getPageSize()));
        ResponseUtils.addHeaders(TOTAL_COUNT, String.valueOf(page.getTotal()));
        ResponseUtils.addHeaders(TOTAL_PAGE, String.valueOf(page.getPages() == 0 ? 1 : page.getPages()));
        // page.getPages()=1表示就1页,前后页都不存在,故也算特殊场景.也为了page.getPages()+1和page.getPages()-1不会对[1,page.getPages()]越界
        if (page.getPages() == 0 || page.getPages() == 1) {
            ResponseUtils.addHeaders(PREV_PAGE, "");
            ResponseUtils.addHeaders(NEXT_PAGE, "");
        } else if (page.getPageNum() == 1) {
            ResponseUtils.addHeaders(PREV_PAGE, "");
            ResponseUtils.addHeaders(NEXT_PAGE, String.valueOf(page.getPages() + 1));
        } else if (page.getPageNum() == page.getPages()) {
            ResponseUtils.addHeaders(PREV_PAGE, String.valueOf(page.getPages() - 1));
            ResponseUtils.addHeaders(NEXT_PAGE, "");
        } else {
            ResponseUtils.addHeaders(PREV_PAGE, String.valueOf(page.getPages() - 1));
            ResponseUtils.addHeaders(NEXT_PAGE, String.valueOf(page.getPages() + 1));
        }
    }
}

第3步：分页查询，HttpHeaders和HttpStatus收集到线程容器中

public List<Student> listStudents(Integer pageNum, Integer PageSize) {
    PageHelper.startPage(PageUtils.getPageNum(pageNum), PageUtils.getPageSize(PageSize), PageUtils.isQueryTotalCount());
    PageHelper.orderBy("age asc");
    
    List<Student> students = userMapper.listStudents();
    PageInfo<Student> studentPageInfo = PageInfo.of(students);
    
    // 收集分页信息到 ThreadLocal
    PageHeaderUtils.setPageHeader(studentPageInfo);
    // 收集HttpStatus到 ThreadLocal
    // ResponseUtils.setResponseCode(num2HttpStatus("200")); // 为了使用一下num2HttpStatus方法
    ResponseUtils.setResponseCode(HttpStatus.OK);
    return students;
}

public class HttpStatusUtils {

    public static HttpStatus num2HttpStatus(String num) {
        HttpStatus httpStatus = HttpStatus.NOT_FOUND;
        for (HttpStatus status : HttpStatus.values()) {
            if (Integer.parseInt(num) == status.value()) {
                return status;
            }
        }
        return httpStatus;
    }
}

第4步：controller层需为@RestController Restful接口

@RestController
@Slf4j
public class SearchController {
    @Autowired
    UserService userService;

    @RequestMapping(value = "/getAllStudents", method = RequestMethod.GET)
    public List<Student> login() {
        List<Student> students = userService.listStudents(1, 10);
        students.forEach(System.out::println);
        return students;
    }
}

第5步：线程容器收纳HttpHeaders和HttpStatus添加到ServerHttpResponse

@ControllerAdvice
public class HttpResponseBodyAdvice implements ResponseBodyAdvice {


    @Override
    public boolean supports(MethodParameter returnType, Class converterType) {
        return true;
    }

    @Override
    public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType, Class clazz,
                                  ServerHttpRequest request, ServerHttpResponse response) {
        HttpHeaders headers = response.getHeaders();

        // 分页信息添加到ServerHttpResponse
        HttpHeaders headersContext = ResponseUtils.getHeaders();
        if (nonNull(headersContext) && !headersContext.isEmpty()) {
            headers.addAll(headersContext);
        }

        // 状态码添加到ServerHttpResponse
        if (nonNull(ResponseUtils.getResponseCode())) {
            response.setStatusCode(ResponseUtils.getResponseCode());
        }
        return body;
    }
}

第6步：测试结果