General paging - front desk

Catalog

One 、PageBean Paging encapsulation class

Two 、PageTag Pagination label

3、 ... and 、Jsp Interface

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Last time I shared with you the background of general paging , Today, let's share with you the front desk

One 、PageBean Paging encapsulation class

First of all, we have to clarify how we need to implement front-end paging , Here are my ideas and methods for implementing front-end paging

1. You need to add a variable to save the last request address

2. You need to get the conditions of the first query

	// You need to add a variable to save the last request address 
	private String Url ;
	// You need to add variables to save the last query criteria 
	 private Map<String, String[]> parameterMap = new HashMap<String, String[]>();

Ideas ： Because we may get the value of multiple conditions , So what is returned is an array of strings , Simultaneous use Map Collection for storage

3. You need to add methods , Get the page number of the largest page ： If you don't understand, you can read the notes

public int MaxPage() {
		// Divide the total data by the total number of rows   If it is equal to 0 It means that you can get this value if you can divide it completely ,
		// If it can't be divided completely, add... To this value 1
		return this.total%this.rows==0?
				this.total/this.rows:
					this.total/this.rows+1;
	}

  4. You need to add methods , Gets the page number of the next page ： If you don't understand, you can read the notes

public int nextPage() {
		// If the current number of pages is less than the maximum number of pages, it indicates that there is a value for the next page , Just +1 Represents the next page ,
		// If it is larger than the maximum page, it will stay on the current page 
		return this.page<this.MaxPage()?this.page+1:this.page;
	}

5. You need to add methods , Get the page number of the previous page ： If you don't understand, you can read the notes

public int previousPage() {
		// If the current number of pages is greater than 1 Note that there is also the value of the previous page , Just -1 Represents the previous page 
		// If it is less than 1 Just stay on the current page 
		return this.page>1?this.page-1:this.page;
	}

At the same time, we define a value saving method in the paged encapsulation class , Five variables or methods required for paging （ Page number page、rows Page size 、 Pagination or not pagination、 Address Url、 Query criteria ParameterMap） For storage , And then again Servlet Just call this method directly in

public void setRequest(HttpServletRequest request) {
		this.setPage(request.getParameter("page"));
		this.setRows(request.getParameter("rows"));
		this.setPagination(request.getParameter("pagination"));
		this.setUrl(request.getRequestURL().toString());
		this.setParameterMap(request.getParameterMap());
	}
	private void setPagination(String pagination) {
		if(StringUtils.isNotBlank("pagination")) {
			this.setPagination(!"false".equals(pagination));
		}
		
	}
	private void setRows(String rows) {
		if(StringUtils.isNotBlank(rows)) {
			this.setRows(Integer.valueOf(rows));
		}
			
		
	}
	private void setPage(String page) {
		if(StringUtils.isNotBlank(page))
			//set Automatic generation method 
			this.setPage(Integer.valueOf(page));
			
	}

Two 、PageTag Pagination label

We use the customization we shared before jsp The knowledge of tags comes from defining a Page label ,PageTag Inherit  BodyTagSupport class , use stringbuffer Medium append Method to achieve the effect of page display . Finally, we just have to jsp Page references PageTag A label will do

package com.zjy.tag;

import java.io.IOException;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.BodyTagSupport;

import com.zjy.util.PageBean;

public class PageTag extends BodyTagSupport{
	private PageBean pageBean;
	
	public PageBean getPageBean() {
		return pageBean;
	}

	public void setPageBean(PageBean pageBean) {
		this.pageBean = pageBean;
	}

	@Override
	public int doStartTag() throws JspException {
		JspWriter out = pageContext.getOut();
		try {
			out.print(toHTML());
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return super.doStartTag();
	}

	private String toHTML() {
		StringBuffer sb = new StringBuffer();
//		 Hidden form Forms , To save the last query criteria 
		sb.append("<form action='"+pageBean.getUrl()+"' id='pageBeanForm' method='post'>");
		sb.append("	<input type='hidden' name='page' value=''>");
		Map<String, String[]> parameterMap = pageBean.getParameterMap();
		if(parameterMap != null && parameterMap.size() > 0) {
			Set<Entry<String, String[]>> entrySet = parameterMap.entrySet();
			for (Entry<String, String[]> entry : entrySet) {
				String key = entry.getKey();// name/likes/page/rows
				String[] values = entry.getValue();
				if(!"page".equals(key)) {
					for (String value : values) {
						sb.append("	<input type='hidden' name='"+key+"' value='"+value+"'>");
					}
				}
			}
		}
		sb.append("</form>");
		
//		 Pagination bar 
		sb.append("<ul class='pagination justify-content-center'>");
		sb.append("	<li class='page-item "+(pageBean.getPage() == 1 ? "disabled" : "")+"'><a class='page-link'");
		sb.append("		href='javascript:gotoPage(1)'> home page </a></li>");
		sb.append("	<li class='page-item "+(pageBean.getPage() == 1 ? "disabled" : "")+"'><a class='page-link'");
		sb.append("		href='javascript:gotoPage("+pageBean.previousPage()+")'>&lt;</a></li>");
		sb.append("	<li class='page-item active'><a class='page-link' href='#'>"+pageBean.getPage()+"</a></li>");
		sb.append("	<li class='page-item "+(pageBean.getPage() == pageBean.MaxPage() ? "disabled" : "")+"'><a class='page-link' href='javascript:gotoPage("+pageBean.nextPage()+")'>&gt;</a></li>");
		sb.append("	<li class='page-item "+(pageBean.getPage() == pageBean.MaxPage() ? "disabled" : "")+"'><a class='page-link' href='javascript:gotoPage("+pageBean.MaxPage()+")'> Tail page </a></li>");
		sb.append("	<li class='page-item go-input'><b> To the first </b><input class='page-link'");
		sb.append("		type='text' id='skipPage' name='' /><b> page </b></li>");
		sb.append("	<li class='page-item go'><a class='page-link'");
		sb.append("		href='javascript:skipPage()'> determine </a></li>");
		sb.append("	<li class='page-item'><b> common "+pageBean.getTotal()+" strip </b></li>");
		sb.append("</ul>");
		
//		 Pagination js Code 
		sb.append("<script type='text/javascript'>");
		sb.append("	function gotoPage(page) {");
		sb.append("		document.getElementById('pageBeanForm').page.value = page;");
		sb.append("		document.getElementById('pageBeanForm').submit();");
		sb.append("	}");
		sb.append("	function skipPage() {");
		sb.append("		var page = document.getElementById('skipPage').value;");
		sb.append("		if (!page || isNaN(page) || parseInt(page) < 1");
		sb.append("				|| parseInt(page) > "+pageBean.MaxPage()+") {");
		sb.append("				alert(' Please enter 1~"+pageBean.MaxPage()+" The number of ');");
		sb.append("			return;");
		sb.append("		}");
		sb.append("		gotoPage(page);");
		sb.append("	}");
		sb.append("</script>");
		
		
		return sb.toString();
	}
}

Remember to define the tag in the tag library ！

3、 ... and 、Jsp Interface

We are Servlet To call our paging method and use    request.setAttribute Save value and forward to jsp Interface  Servlet The code in ：

	
	    PageBean pageBean = new PageBean();
	    pageBean.setRequest(request);
	 
	   request.setAttribute("pageBean", pageBean);
	   request.getRequestDispatcher("BookList.jsp").forward(request, response);

Interface reference ：

	<z:Page pageBean="${PageBean}"></z:Page>

summary ： The first query of front-end paging is the key and difficult point , We need to get the keywords of the query criteria, as well as the initial page number and total row number , Pagination or not , For the second and third pagination, we just need to change the page number , Other conditions need not be changed . We put the implementation effects of methods and interfaces into classes , Finally, just call , Very convenient ！