About debugging the assignment of pagenum and PageSize of the formal parameter pageweb ＜ T > (i.e. page encapsulation generic) in the controller

problem : The console shows that we have found the value , But the final returned data is null

 

Question why :PageWeb Of pageNum and pageSize The value of is affected by the front-end value transmission ,pageNum,totalSize suffer mybatisPlus Of page Method influence , As a result, the data cannot be displayed

Controller Class

@Slf4j
@RestController
@RequestMapping("notice")
public class NoticeController {

    @Resource
    private NoticeService noticeService;
/**
     *  View notification announcement interface 
     *
     * @param pageWeb
     * @return
     */
   
    @GetMapping("getManagerNotice")
    public ResultJson getManagerNotice(@RequestBody PageWeb<Notice> pageWeb) {

        Page<Notice> page = new Page<>(pageWeb.getPageNum(), pageWeb.getPageSize());
        QueryWrapper<Notice> noticeQueryWrapper = new QueryWrapper<>();
        noticeQueryWrapper.eq("state", NoticeConstant.PUBLIC_ALREADY);

        if (!StringUtils.isEmpty(pageWeb.getParams().getTitle())) {
            noticeQueryWrapper.like("title", pageWeb.getParams().getTitle());
        }
        if (!StringUtils.isEmpty(pageWeb.getParams().getContent())) {
            noticeQueryWrapper.like("content", pageWeb.getParams().getContent());
        }
        if (!StringUtils.isEmpty(pageWeb.getParams().getFromId())) {
            noticeQueryWrapper.eq("from_id", pageWeb.getParams().getFromId());
        }
        if (!StringUtils.isEmpty(pageWeb.getParams().getToId())) {
            noticeQueryWrapper.eq("to_id", pageWeb.getParams().getToId());
        }
        if (!StringUtils.isEmpty(pageWeb.getParams().getCreateTime())) {
            noticeQueryWrapper.like("create_time", pageWeb.getParams().getCreateTime());
        }
        IPage<Notice> ipage = noticeService.page(page, noticeQueryWrapper);

        return ResultJson.ok(PageWeb.bulidPageWeb(ipage));
    }

}

PageWeb<T>  Encapsulate generic classes separately

package com.fourthgroup.schoolmanagementsystem.common.web;

import com.baomidou.mybatisplus.core.metadata.IPage;
import com.fourthgroup.schoolmanagementsystem.common.constant.WebConstant;
import lombok.Data;

import java.util.List;

@Data
public class PageWeb<T> {
    private long pageNum=1L;
    private long pageSize=20L;
    private long totalSize;
    private T params;
    private List<T> records;


    public static PageWeb bulidPageWeb(IPage page) {
        return new PageWeb(page.getCurrent(), page.getSize(), page.getTotal(), page.getRecords());
    }

    public PageWeb(long pageNum, long pageSize, long totalSize, List<T> records) {
       
        this.pageNum = pageNum;
        this.pageSize = pageSize;
        this.totalSize = totalSize;
        this.records = records;
    }
}

stay Postman Zhongchuan ginseng (Json Format )

 

  At this time, we did not pass pageNum and pageSize, And we are Controller Medium

Page<Notice> page = new Page<>(pageWeb.getPageNum(), pageWeb.getPageSize());

Of page What is passed in the constructor is pageWeb.getPageNum(), pageWeb.getPageSize(),

We debug debugged , stay page Method line break point

 

At this time, the value we get is that we are PageWeb Value assigned inside , But we Postman No value transfer , So the value we wrote before , Will be Postman The values in the are overwritten ,

Then we are PageWeb Break point in the variable of

pageNum Turned into 1,totalSize Turned into 2, but pageSize yes 0, This leads to the fact that our data cannot be displayed

because page After method execution , The obtained value will be overwritten automatically PageWeb Value ,

---

---

resolvent :

Assign value in constructor , And determine null assignment

 

package com.fourthgroup.schoolmanagementsystem.common.web;

import com.baomidou.mybatisplus.core.metadata.IPage;
import com.fourthgroup.schoolmanagementsystem.common.constant.WebConstant;
import lombok.Data;

import java.util.List;

@Data
public class PageWeb<T> {
    private long pageNum;
    private long pageSize;
    private long totalSize;
    private T params;
    private List<T> records;


    public static PageWeb bulidPageWeb(IPage page) {
        return new PageWeb(page.getCurrent(), page.getSize(), page.getTotal(), page.getRecords());
    }

    public PageWeb(long pageNum, long pageSize, long totalSize, List<T> records) {
        if (pageNum== 0) {
            this.pageNum = Long.valueOf(WebConstant.DEFAULT_PAGE_NO);
        } else {
            this.pageNum = pageNum;
        }

        if (pageSize == 0) {
            this.pageSize = Long.valueOf(WebConstant.DEFAULT_PAGE_SIZE);
        }else{
            this.pageSize = pageSize;
        }

        this.totalSize = totalSize;
        this.records = records;
    }
}

 

continue debug 

 

Because we judge empty in the constructor , So he will assign values to us automatically

Long.valueOf(WebConstant.DEFAULT_PAGE_NO), The default setting here is 1; Long.valueOf(WebConstant.DEFAULT_PAGE_SIZE), The default setting here is 20

On the whole ,records There is ArrayList The value of