JavaScript implements paging function

This article mainly introduces the implementation of JS paging (synchronous and asynchronous). Friends in need can refer to the following

Paging technology is divided into back-end paging and front-end paging.

Front-end paging

Taking out all the data at once and then paging it through js has its drawbacks: Assume there is a product table dbgoods, which stores 999.99 million pieces of data. Execute the query statement
select *from dbgoods where 1=1 Receive the query structure using List<goods>list </goods>, and the server will pass such a huge amount of data to the front end, It will cause large download volume (traffic is money), high server pressure, etc.

Back-end paging

Back-end paging only queries one page of values ​​per request, taking mysql as an example (starting with the first query, querying 8 items)

select * from dbgoods order by id limit 0,8;

Backend synchronization paging

Principle: There needs to be a Bean to record paging information,

public class PageBean{
 private long total;  //总记录数
 private List<T> list; //结果集
 private int pageNum; // 第几页
 private int pageSize; // 每页记录数
 private int pages;  // 总页数
 private int size;  // 当前页的数量 <= pageSize，该属性来自ArrayList的size属性

When we load for the first time, the paging data of the first page is loaded:

It is worth noting that

In the past, I wrote the sql statement like this to get the total number of items:

select *from dbgoods ;
//用Lits<goods> lists去存储 得到的数据，如果数据有几万条，
//为了得到一个数字，去开辟这么大的空间，实属浪费
PageBean page=new PageBean();
page.setTotal=lists.size();

In fact, the correct way to open it is:

select count(*) from dbgoods where 1=1 ;
//查询语句返回的是一个表的总记录数，int型，
//where 1==1是为了查询搜索，做sql语句拼接

Synchronous implementation of asynchronous implementation, passing the currentpage parameters from the jsp interface to the servlet, the servlet obtains the parameters through the request request, and then passes the data to the jsp interface after querying the dao layer database.

The interface effect seen by the browser is: jsp--->servlet----->jsp (jump, poor user experience)

If there is a search box, When performing search paging, click the search button. When the query data is transferred to the jsp interface, the jsp is already a brand new page, and the text box content in the search box has disappeared. The solution is to change the value of the text box when clicking search. Also put it in the request request, send it to the servlet together, and then pass it to the new jsp through the servlet (super cumbersome)

Two solutions:

(1) Make two interfaces the same, one is used for paging when all data is displayed. When the query is clicked, another page is used after getting the data (the click event on the next page is to perform the search) ) to display

(2) Use session: When you click on the search query, record the search conditions in the session. When you click on the next page, judge the value of the session. If it is empty, execute all data On the next page, if it is not empty, the value of the session is taken out and used as the query condition. The next page executes the query statement with the search conditions. Trouble: Session destruction is difficult to control and prone to bugs

In short, using synchronization to implement paging will cause all kinds of unhappiness

Ajax asynchronous paging

//jsp界面一个函数，传递查询页码，绘制表格
 function InitTable(currentpage)
     {
      $.ajax({
       type:"get",
       url:"CustomServlet?type=search&currentpage="+currentpage,
       async:true,
       dataType:"json",
       success:function(data)
       {
        DrawTable(data); //绘制表格
       }
      });
     }
function DrawTable(data) //根据传递过来的json绘制表格
     {
      //给总页数赋值
      $("#custom_all").text(data.pagelist.total);
     //给当前页赋值
$("#custom_currunt_page").text(data.pagelist.pageNum);
     //给总页数赋值
 $("#custom_all_page").text(data.pagelist.pages);
      var _th="<th><input id=&#39;cb_all&#39; type=&#39;checkbox&#39;></th>"
      +"<th>ID</th>"
      +"<th>客户名称</th>"
      +"<th>公司名称</th>"
      +"<th>联系人</th>"
      +"<th>性别</th>"
      +"<th>联系电话</th>"
      +"<th>手机</th>"
      +"<th>QQ</th>"
      +"<th>电子邮箱</th>"
      +"<th>通讯地址</th>"
      +"<th>创建时间</th>";
      document.getElementsByTagName("tbody")[0].innerHTML=_th;
       for(var i=0;i<data.pagelist.list.length;i++)
       {
        var customerCreatetime= format(data.pagelist.list[i].customerCreatetime, &#39;yyyy-MM-dd&#39;);
        var _tr=document.createElement(&#39;tr&#39;);
        msg="<td><input type=&#39;checkbox&#39;></td><td>"+data.pagelist.list[i].customerId+"</td><td>"+data.pagelist.list[i].customerName+"</td><td>"+data.pagelist.list[i].customerCompanyname+"</td><td>"+data.pagelist.list[i].customerContactname+"</td><td>"+data.pagelist.list[i].customerSex+"</td><td>"+data.pagelist.list[i].customerTelephone+"</td><td>"+data.pagelist.list[i].customerPhone+"</td><td>"+data.pagelist.list[i].customerQq+"</td><td>"+data.pagelist.list[i].customerEmail+"</td><td>"+data.pagelist.list[i].customerAddress+"</td><td>"+customerCreatetime+"</td>"
       _tr.innerHTML=msg;         
        document.getElementsByTagName("tbody")[0].appendChild(_tr);
       }
     }

When loading for the first time, the default call is

//初始化表格
      InitTable(1);

It is worth noting that the key point is:

When we search, we define a global variable mydata with a scope of page

var mydata="";

Let’s look at the event code of clicking the search button

btns.eq(1).click( //搜索按钮点击事件
          function()
         {
      //custom_dialog_form是搜索的form表单，将其搜索条件序列化后赋值给一个全局变量     mydata=$("#custom_dialog_form").serialize();
           $.ajax({
            type:"post",
            url:"CustomServlet?type=search&currentpage=1",
            async:true,
            dataType:"json",
            data:mydata, //传递数据
            success:function(data)
            {
             DrawTable(data);
             $("#custom_dialog").css("display","none");
            }
           });
         }
          );

Solve the problem that the next page in the case of synchronized search accesses the next page of all data:

 function InitTable(currentpage) //无搜索条件下的查询，传递一个页码
     {
      $.ajax({
       type:"get",
       url:"CustomServlet?type=search&currentpage="+currentpage,
       async:true,
       dataType:"json",
       success:function(data)
       {
        DrawTable(data);
       }
      });
     }
     function InitTableSearch(currentpage)//有搜索添加的查询，传递页码
     {
       $.ajax({
        type:"post",
        url:"CustomServlet?type=search&currentpage="+currentpage,
        async:true,
        dataType:"json",
        data:mydata,
        success:function(data)
        {
         DrawTable(data);
         $("#custom_dialog").css("display","none");
        }
       });
     }
//下一页
      $("#custom_btn_next").click(
        function ()
        {
         var currentpage=$("#custom_currunt_page").text(); //获取页面的当前页的值
         var pages=$("#custom_all_page").text(); //获取总页数
         currentpage++;
         if(currentpage<=pages)
          {
          if(mydata=="") //判断全局变量mydata是否为空，空表示没有进行搜索查询
          {
          InitTable(currentpage);
          }
         else
          {
           InitTableSearch(currentpage); //进行条件搜索
          }
          }
        });

Because it is Asynchronous refresh, so the global variable mydata has a value. If you manually refresh the page and reload it, mydata will be initialized to empty, and the unconditional search statement will be executed by default. Cleverly solves the problem of searching and displaying all the next pages. The same goes for the previous page, home page and last page.

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