SpringBoot 把PageHelper分页信息返回给前端

第1步：定义收纳HttpHeaders和HttpStatus的 线程容器

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


public class ResponseContext {
    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：封装 把分页信息转储到线程容器 的方法

import com.github.pagehelper.Page;
import com.github.pagehelper.PageInfo;
import com.zhangziwa.practisesvr.utils.response.ResponseContext;

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(Page<E> page) {
        if (page == null) {
            return;
        }
        ResponseContext.addHeaders(PAGE_NUM, String.valueOf(page.getPageNum()));
        ResponseContext.addHeaders(PAGE_SIZE, String.valueOf(page.getPageSize()));
        ResponseContext.addHeaders(TOTAL_COUNT, String.valueOf(page.getTotal()));
        ResponseContext.addHeaders(TOTAL_PAGE, String.valueOf(page.getPages() == 0 ? 1 : page.getPages()));
        if (page.getPages() == 0 || page.getPages() == 1) {
            ResponseContext.addHeaders(PREV_PAGE, "");
            ResponseContext.addHeaders(NEXT_PAGE, "");
        } else if (page.getPageNum() == 1) {
            ResponseContext.addHeaders(PREV_PAGE, "");
            ResponseContext.addHeaders(NEXT_PAGE, String.valueOf(page.getPages() + 1));
        } else if (page.getPageNum() == page.getPages()) {
            ResponseContext.addHeaders(PREV_PAGE, String.valueOf(page.getPages() - 1));
            ResponseContext.addHeaders(NEXT_PAGE, "");
        } else {
            ResponseContext.addHeaders(PREV_PAGE, String.valueOf(page.getPages() - 1));
            ResponseContext.addHeaders(NEXT_PAGE, String.valueOf(page.getPages() + 1));
        }
    }

    /**
     * 设置分页头信息
     * @param page 分页对象
     * @param <E> 分页对象的数据类型
     */
    public static <E> void setPageHeader(PageInfo<E> page) {
        if (page == null) {
            return;
        }
        ResponseContext.addHeaders(PAGE_NUM, String.valueOf(page.getPageNum()));  // 设置当前页码
        ResponseContext.addHeaders(PAGE_SIZE, String.valueOf(page.getPageSize()));  // 设置每页显示数量
        ResponseContext.addHeaders(TOTAL_COUNT, String.valueOf(page.getTotal()));  // 设置总记录数
        ResponseContext.addHeaders(TOTAL_PAGE, String.valueOf(page.getPages() == 0 ? 1 : page.getPages()));  // 设置总页数
        // 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) {
            ResponseContext.addHeaders(PREV_PAGE, "");  // 上一页
            ResponseContext.addHeaders(NEXT_PAGE, "");  // 下一页
        } else if (page.getPageNum() == 1) {
            ResponseContext.addHeaders(PREV_PAGE, "");  // 上一页
            ResponseContext.addHeaders(NEXT_PAGE, String.valueOf(page.getPages() + 1));  // 下一页
        } else if (page.getPageNum() == page.getPages()) {
            ResponseContext.addHeaders(PREV_PAGE, String.valueOf(page.getPages() - 1));  // 上一页
            ResponseContext.addHeaders(NEXT_PAGE, "");  // 下一页
        } else {
            ResponseContext.addHeaders(PREV_PAGE, String.valueOf(page.getPages() - 1));  // 上一页
            ResponseContext.addHeaders(NEXT_PAGE, String.valueOf(page.getPages() + 1));  // 下一页
        }
    }
}

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

@Service
@Slf4j
public class UserServiceImpl implements UserService {

    @Autowired
    private UserMapper userMapper;

	# PageInfo方式
    @Override
    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
        // ResponseContext.setResponseCode(num2HttpStatus("200")); // 为了使用一下num2HttpStatus方法
        ResponseContext.setResponseCode(HttpStatus.OK);
        return students;
    }

	# Page 方式
    @Override
    public List<Student> listStudents2(Integer pageNum, Integer PageSize) {
        PageHelper.startPage(PageUtils.getPageNum(pageNum), PageUtils.getPageSize(PageSize), PageUtils.isQueryTotalCount());
        PageHelper.orderBy("age asc");

        Page<Student> students = (Page<Student>) userMapper.listStudents();
        
        PageHeaderUtils.setPageHeader(students);
        ResponseContext.setResponseCode(HttpStatus.OK);
        return students;
    }

	# 多数据源聚合时的手工分页
    @Override
    public List<Student> listStudents3(Integer pageNum, Integer pageSize) {
        // 模拟数据聚合
        List<Student> students3 = new ArrayList<>();
        List<Student> students1 = userMapper.listStudents();
        List<Student> students2 = userMapper.listStudents();

        students3.addAll(students1);
        students3.addAll(students2);

        Page<Student> studentsPage = PageHeaderUtils.manualPage(students3, pageNum, pageSize);
        PageHeaderUtils.setPageHeader(studentsPage);
        ResponseContext.setResponseCode(HttpStatus.OK);
        return studentsPage;
    }
}

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;
    }
}

单次分页查询可以使用PageHelper，但是如果多数据源数据聚合时PageHelper不再适用，可以使用手工分页的方式进行分页。

# 使用PageHelper进行分页时
PageHelper.startPage(PageUtils.getPageNum(pageNum), PageUtils.getPageSize(PageSize), PageUtils.isQueryTotalCount());

# 数据聚合场景下的手工分页
public class PageHeaderUtils {
    // 也适合EmptyList场景 Page{count=true, pageNum=1, pageSize=10, startRow=0, endRow=0, total=0, pages=0, reasonable=null, pageSizeZero=null}
    public static <E> Page<E> manualPage(List<E> res, Integer pageNum, Integer pageSize) {
        if (res == null) {
            res = new ArrayList<>();
        }

        int pageNumber = PageUtils.getPageNum(pageNum);
        int sizePerPage = PageUtils.getPageSize(pageSize);
        int totalSize = res.size();

        List<E> pageElements = res.stream().skip((long) (pageNumber - 1) * sizePerPage).limit(sizePerPage).toList(); // 分页

        Page<E> page = new Page<>();
        page.setPageNum(pageNumber);
        page.setPageSize(sizePerPage);
        page.setTotal(totalSize);
        page.setPages((totalSize / pageSize + ((totalSize % pageSize == 0) ? 0 : 1)));
        page.addAll(pageElements);

        return page;
    }
}

第4步：检查controller层， @Controller → @RestController

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

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

    @RequestMapping(value = "/getAllStudents2", method = RequestMethod.GET)
    public List<Student> getAllStudents2() {
        List<Student> students = userService.listStudents2(1, 10);
        students.forEach(System.out::println);
        return students;
    }

    @RequestMapping(value = "/getAllStudents3", method = RequestMethod.GET)
    public List<Student> getAllStudents3() {
        List<Student> students = userService.listStudents3(1, 5);
        students.forEach(System.out::println);
        return students;
    }
}

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

import org.springframework.core.MethodParameter;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.servlet.mvc.method.annotation.ResponseBodyAdvice;

import static java.util.Objects.nonNull;

@ControllerAdvice
public class ResponsePostAdvice 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 = ResponseContext.getHeaders();
        if (nonNull(headersContext) && !headersContext.isEmpty()) {
            headers.addAll(headersContext);
        }

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

第6步：清理 线程容器

定义拦截器执行ResponseContext.clear();，用于资源清理

import com.zhangziwa.practisesvr.utils.response.ResponseContext;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import org.springframework.http.HttpHeaders;
import org.springframework.stereotype.Component;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

@Component
public class ResponsePostInterceptor implements HandlerInterceptor {

    //在Controller执行之前调用，如果返回false，controller不执行
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.err.println("***ResponsePostInterceptor.preHandle***");
        return true;
    }

    //controller执行之后，且页面渲染之前调用
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.err.println("***ResponsePostInterceptor.postHandle***");
    }

    //页面渲染之后调用，一般用于资源清理操作
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.err.println("***ResponsePostInterceptor.afterCompletion***");
        ResponseContext.clear();
    }
}

注册拦截器

@Configuration
public class WebMvcConfig implements WebMvcConfigurer {
    @Autowired
    private ResponsePostInterceptor responsePostInterceptor;

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(responsePostInterceptor);
    }
}

第7步：测试结果