General paging implementation

Why universal paging ？

1） In order to improve query performance and save network traffic , Query only the specified number of records at a time , Not all of them , It is very useful when the quantity is large
2） When clicking on the next page or the data of the specified page , Will bring all the query conditions , Execute the query again

Final effect display ：

 

The illustration

  Effect display

Realize the idea ：（ understand ）

How to encapsulate a general paging query method , Write a query first sql sentence , Put the query criteria and paging entities as parameters of the method .

Determine if pagination is needed

1. No paging , Direct inquiry , First traversal , And then return the result set

2. Pagination , Total pages of query , If the total record is 0, Directly return an empty result set , If not for 0, First write the number of pages that need to be displayed sql sentence , Then query the data of the current page , Returns the result set of the current page （1~10 page ）.

  Encapsulate a paging information entity , Because we need to use its properties later

package com.zking.utils;

import java.util.Map;

import javax.servlet.http.HttpServletRequest;

import com.mysql.jdbc.StringUtils;
public class PageBean {
	
	/**
	 *  Page number 
	 */
	private int page = 1;

	/**
	 *  Number of records per page 
	 */
	private int rows = 10;

	/**
	 *  Total number of records 
	 */
	private int total = 0;

	/**
	 *  Pagination or not 
	 */
	private boolean pagination = false;
	
	/**
	 *  Record the inquiry url, So that it can be used again when clicking paging 
	 */
	private String url;
	
	/**
	 *  Store request parameters , Used to generate elements in hidden fields 
	 */
	private Map<String,String[]> parameterMap;
	
	/**
	 *  Based on the incoming Request Initialize paging object 
	 * @param request
	 */
	public void setRequest(HttpServletRequest request) {
		
		if(!StringUtils.isNullOrEmpty(request.getParameter("page"))) {
			this.page = Integer.valueOf(request.getParameter("page"));
		}
		if(!StringUtils.isNullOrEmpty(request.getParameter("rows"))) {
			this.rows = Integer.valueOf(request.getParameter("rows"));
		}
		if(!StringUtils.isNullOrEmpty(request.getParameter("pagination"))) {
			this.pagination = Boolean.valueOf(request.getParameter("pagination"));
		}
		
		this.url = request.getRequestURI();
		this.parameterMap = request.getParameterMap();
		
		request.setAttribute("pageBean", this);
	}


	public int getPage() {
		return page;
	}


	public void setPage(int page) {
		this.page = page;
	}


	public int getRows() {
		return rows;
	}


	public void setRows(int rows) {
		this.rows = rows;
	}


	public int getTotal() {
		return total;
	}


	public void setTotal(int total) {
		this.total = total;
	}

	public boolean isPagination() {
		return pagination;
	}

	public void setPagination(boolean pagination) {
		this.pagination = pagination;
	}
	
	public String getUrl() {
		return url;
	}

	public void setUrl(String url) {
		this.url = url;
	}

	public Map<String, String[]> getParameterMap() {
		return parameterMap;
	}

	public void setParameterMap(Map<String, String[]> parameterMap) {
		this.parameterMap = parameterMap;
	}

	// Calculate the starting line number 
	public int getStartIndex() {
		if(this.page > this.getTotalPage()) { 
			this.page = this.getTotalPage();
		}
		if(this.page < 1) {
			this.page = 1;
		}
		return (this.page - 1) * this.rows;
	}
	
	// Get total pages 
	public int getTotalPage() {
		if (this.getTotal() % this.rows == 0) {
			return this.getTotal() / this.rows;
		} else {
			return this.getTotal() / this.rows + 1;
		}
	}

	// The previous page 
	public int getPreviousPage() {
		return this.page - 1 > 0 ? this.page - 1 : 1;
	}
	
	// The next page 
	public int getNextPage() {
		return this.page + 1 > getTotalPage() ? getTotalPage() : this.page + 1;
	}

}

Version of a

public List<Book> queryBook(String bname,PageBean pb){
		String sql="select * from t_book";
		
		if(!StringUtils.isNullOrEmpty(bname)) {
			sql+=" where bname like ?";
		}
		
		List<Book> list=new ArrayList<>();
		Connection con=null;
		PreparedStatement ps=null;
		ResultSet rs=null;
		
		//false || true  perhaps , One is true is true , No more calculations in the future , An expression on the right of false recalculation .
		//true && true   And , First calculate the left , If the left one is not satisfied , It will not be calculated later ; If meet , You must meet two requirements 
		if(pb ==null ||  !pb.isPagination()) {// No paging 
			try {
				con=DBUtil.getConection();
				ps=con.prepareStatement(sql);
				
				/**
				 *  because mysql The database is automatically added as follows sql
				 * select * from t_book where bname like '%strName%';
				 *  So there is no need to escape "%";
				 */
				if(!StringUtils.isNullOrEmpty(bname)) {
					ps.setObject(1, "%"+bname+"%");
				}
				
				rs=ps.executeQuery();
				while (rs.next()) {
					Book b=new Book();
					b.setBid(rs.getInt(1));
					b.setBname(rs.getString(2));
					b.setPrice(rs.getDouble(3));
					list.add(b);
				}
				return list;
			} catch (Exception e) {
				e.printStackTrace();
			}
		}else {
			try{// Paging required 
			// Main page 
			String countsql="select count(*) from ("+sql+") p";
			con=DBUtil.getConection();
			ps=con.prepareStatement(countsql);
			
			if(!StringUtils.isNullOrEmpty(bname)) {
				ps.setObject(1, bname+"%");
			}
			
			rs=ps.executeQuery();
			if(rs.next()) {
				pb.setTotal(rs.getInt(1));
			}
			
			if(pb.getTotal()<=0) {// No record 
				return list;
			}
			// Query the data of the current page 
			String pageql=sql+" limit "+pb.getStartIndex()+","+pb.getRows();
			ps=con.prepareStatement(pageql);
			if(!StringUtils.isNullOrEmpty(bname)) {
				ps.setObject(1, bname+"%");
			}
			rs=ps.executeQuery();
			while (rs.next()) {
				Book b=new Book();
				b.setBid(rs.getInt(1));
				b.setBname(rs.getString(2));
				b.setPrice(rs.getDouble(3));
				list.add(b);
			}
		}catch(Exception e){
		e.printStackTrace();
		}finally {
			DBUtil.closeDB(rs, ps, con);
		}
		}
		return list;
	}

Version 2 ：

General query ideas

take sql sentence , Parameters , Paging object , The converter passes this method as a parameter , Determine if pagination is needed ,

if necessary , To write sql（ Number of display bars ） Query the data of the current page , Convert the data result set into an object , Show current page ;

If you don't need to , Execute the query , Directly return the result set .

public class BaseDao {
/*
	 *  Adapter ：
	 *  I don't know how to convert the database result set into an object , I need it covert This interface helps me convert .
	 * 
	 */
	public interface IConvert<T>{

	public List<T> convert(ResultSet rs) throws SQLException;
	}
	
	public final <T> List<T> query(
			String sql,//sql
			Object[] params,// Parameters 
			PageBean pb,// Paging object 
			IConvert<T> convert// converter 
			){
		
		List<T> list=new ArrayList<>();
		Connection con=null;
		PreparedStatement ps=null;
		ResultSet rs=null;
		
		/**
		 * || Condition or    As long as the first condition is met , The latter conditions are no longer judged 
		 * &&  Conditions and  	 To meet the first condition and the second condition 
		 */
		if(pb ==null ||  !pb.isPagination()) {// No paging 
			try {
				con=DBUtil.getConection();
				ps=con.prepareStatement(sql);
				
				/*
				 *  loop Object[] Array , Put the parameters one by one sql
				 */
				int i=1;
				for (Object param : params) {
					ps.setObject(i, param);
					i++;
				}
				
				rs=ps.executeQuery();
				// Convert the result set of query to database into object 
				list=convert.convert(rs);
				return list;
			} catch (Exception e) {
				e.printStackTrace();
			}finally {
				DBUtil.closeDB(rs, ps, con);
			}
	}else {
		try{// Paging required 
		// Main page 
		String countsql="select count(*) from ("+sql+") p";
		con=DBUtil.getConection();
		ps=con.prepareStatement(countsql);
		
		int i=1;
		for (Object param : params) {
			ps.setObject(i, param);
			i++;
		}
		
		rs=ps.executeQuery();
		if(rs.next()) {
			pb.setTotal(rs.getInt(1));
		}
		
		if(pb.getTotal()<=0) {// No record 
			return list;
		}
		// Query the data of the current page 
		String pageql=sql+" limit "+pb.getStartIndex()+","+pb.getRows();
		ps=con.prepareStatement(pageql);
		
		int j=1;
		for (Object param : params) {
			ps.setObject(j, param);
			j++;
		}
		rs=ps.executeQuery();
		
		list=convert.convert(rs);
		
	}catch(Exception e){
	e.printStackTrace();
	}finally {
		DBUtil.closeDB(rs, ps, con);
	}
	}
		
	return list;
}
}

Test class

public class Bookdao extends BaseDao{
/**
	 * @param bname  Search keywords 
	 * @param pb  Paging object 	
	 * @return
	 */
	public List<Book> getbook(String bname,PageBean pb){
		String sql="select * from t_book";
		List<Object> params=new ArrayList<>();
		if(!StringUtils.isNullOrEmpty(bname)) {// A method to determine whether the string is an empty reference or the value is empty 
			sql+=" where bname like ?";
			params.add(bname+"%");// Add query criteria 
		}
		
		//params.toArray() When using Arraylist Array , You can get an actual array 
		/**
		 *  After the subclass inherits the parent class ,this The meaning expressed by the object , It mainly depends on this What kind of method is called . If you specify a parent method , It means calling the parent method 
		 *  If you specify a subclass method , It means calling subclass methods 
		 */
		List<Book> list=this.query(sql, params.toArray(), pb, new IConvert<Book>() {
			@Override
			public List<Book> convert(ResultSet rs) throws SQLException {
				List<Book> list = new ArrayList<>();
				while (rs.next()) {
					Book b=new Book();
					b.setBid(rs.getInt(1));
					b.setBname(rs.getString(2));
					b.setPrice(rs.getDouble(3));
					list.add(b);
				}
				return list;
			}
		});
		return list;
	}

    public static void main(String[] args) {
	Bookdao bs=new Bookdao();
	PageBean pageBean = new PageBean();
	System.out.println(pageBean.isPagination());// result ：flase
	pageBean.setPagination(true);
	List<Book> queryBook = bs.getbook("",pageBean );
	System.out.println(queryBook);
}
}

matters needing attention ：

|| Condition or   As long as the first condition is met , The latter conditions are no longer judged
&& Conditions and      To meet the first condition and the second condition

Adapter ：

effect ： I don't know how to convert the database result set into an object , I need it covert This interface helps me convert .

Code display

 public interface IConvert<T>{
    
	public List<T> convert(ResultSet rs) throws SQLException;

	}


public final <T> List<T> query(
			String sql,//sql
			Object[] params,// Parameters 
			PageBean pb,// Paging object 
			IConvert<T> convert// converter 
			){
	    // Convert the result set of query to database into object 
				list=convert.convert(rs);
}

this object

public class Bookdao extends BaseDao{

	/**
	 *
	 * @param bname  Search keywords 
	 * @param pb  Paging object 	
	 * @return
	 */
	public List<Book> getbook(String bname,PageBean pb){
		String sql="select * from t_book";
		List<Object> params=new ArrayList<>();
		if(!StringUtils.isNullOrEmpty(bname)) {// A method to determine whether the string is an empty reference or the value is empty 
			sql+=" where bname like ?";
			params.add(bname+"%");// Add query criteria 
		}
		
		//params.toArray() When using Arraylist Array , You can get an actual array 
		List<Book> list=this.query(sql, params.toArray(), pb, new IConvert<Book>() {
			@Override
			public List<Book> convert(ResultSet rs) throws SQLException {
						return list;
			}
		});
		return list;
	}

this After the subclass inherits the parent class ,this The meaning expressed by the object , It mainly depends on this What kind of method is called . If you specify a parent method , It means calling the parent method ; If you specify a subclass method , It means calling subclass methods .

Common code

• As long as it is paging , The total number of records will be counted , The statistics of total records are in business sql There is a select count(*) There are rules to follow , Can be used in general

• As long as it is paging , Then encapsulate paging sql There are also rules to follow （ In the business sql After add limit Clause is enough ）, Can be used in general

 Book page

	<h2> Student information </h2>

	<form action="<%=request.getContextPath()%>/BookServlet" method="post">
		<input type="text" name="bname"> <input type="submit"
			value=" Inquire about ">
	</form>

	<!-- If the collection is empty , will servlet Data is loaded into the page   -->
	<c:if test="${empty list }">
	<jsp:forward page="/BookServlet"></jsp:forward>
	</c:if> 
	<table border="1" style="width: 100%" >
		<tr>
			<td> Number </td>
			<td> Title </td>
			<td> Price </td>
		</tr>

		<c:forEach items="${list }" var="b">
			<tr>
				<td>${b.bid }</td>
				<td>${b.bname }</td>
				<td>${b.price }</td>
			</tr>
		</c:forEach>
	</table>

	 <div style="text-align: right; width:98%;">
		 The first ${pageBean.page} page &nbsp;&nbsp;&nbsp;
		 common ${pageBean.totalPage} Bar record &nbsp;&nbsp;&nbsp;
		<a href="javascript:goPage(1)"> home page </a>&nbsp;&nbsp;&nbsp;
		<a href="javascript:goPage(${pageBean.previousPage })"> page-up key </a>&nbsp;&nbsp;&nbsp; 
		<a href="javascript:goPage(${pageBean.nextPage })"> next page </a>&nbsp;&nbsp;&nbsp; 
		<a href="javascript:goPage(${pageBean.totalPage })"> Tail page </a>&nbsp;&nbsp;&nbsp;
		 The first <input type="text" size="2" id="pageNumber" onkeyup="toPage(event,this.value)" /> 
		<a href="#">GO</a>
	</div>
	
	<!--  Hidden form for paging  -->
	<form action="${pageBean.url}" id="pagingForm" method="post">
		<input type="hidden" name="page" value="${pageBean.page}"/>
		<!--  First, only consider the query parameters of this function , No consideration of commonality （ Different functions have different parameters ） -->
		<input type="hidden" name="bname" value="<%=request.getParameter("bname")%>"/>
	</form> 
	
	<script type="text/javascript">
 	function goPage(pageNum){
		let form=document.getElementById("pagingForm");
		form.page.value=pageNum;
		form.submit();
	}
 	
 	/**
 	* Keyboard click event 
 	*event Event object 
 	*/
 	function toPage(e,pageNumber){
 		 if(e.keyCode == 13){// The Astor value of the Enter key 
 			goPage(pageNumber);
 		 } 
 	}
 	
	</script> 

Interactive with database BookServlet

@WebServlet("/BookServlet")
public class BookServlet extends HttpServlet {

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		doPost(request, response);
	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
	
	PageBean pb=new PageBean();
	pb.setRows(5);
	pb.setPagination(true);
	pb.setRequest(request);//PageBean The saved 
	
	String bname=request.getParameter("bname");
	
	Bookdao b=new Bookdao();
	List<Book> list = b.query1Book(bname,pb);
	
	request.setAttribute("list", list);

	request.getRequestDispatcher("Book.jsp").forward(request, response);
	}

}