Servlet – 分页示例

分页是一系列相互连接并具有相似内容的页面。分页是一种将多条记录列表拆分为子项的技术。例如，您在 Google 上使用关键字搜索并收到数以万计的结果。重要的是要注意，即使页面部分的内容被分成不同的页面，我们仍将其定义为分页。

Java中的分页

为了将大量记录分成多个部分，我们使用分页。它允许用户仅显示部分记录。在单个页面上加载所有记录可能需要一些时间，因此始终建议创建分页。在Java中，我们可以轻松开发分页示例。在这个分页示例中，我们使用 MySQL 数据库来获取记录。

例子

步骤 1 ：在 Mysql 中创建一个表

create table employee(empid int(11),empname varchar(20),empsalary int(11),empdept varchar(20));

第 2 步：创建一个 JavaBean 类，用于为数据库设置值并从数据库中获取值。

Java

public class Employee {
    int employeeId;
    String employeeName;
    int salary;
    String deptName;
  
    public String getDeptName() { return deptName; }
  
    public void setDeptName(String deptName)
    {
        this.deptName = deptName;
    }
  
    public int getEmployeeId() { return employeeId; }
  
    public void setEmployeeId(int employeeId)
    {
        this.employeeId = employeeId;
    }
  
    public String getEmployeeName() { return employeeName; }
  
    public void setEmployeeName(String employeeName)
    {
        this.employeeName = employeeName;
    }
  
    public int getSalary() { return salary; }
  
    public void setSalary(int salary)
    {
        this.salary = salary;
    }
}

第 3 步：为从数据库获取连接创建一个工厂类。

Java

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
  
public class ConnectionFactory {
  
    // static reference to itself
    private static ConnectionFactory instance = new ConnectionFactory();
  
    String url = "jdbc:mysql://localhost:3306/ashok";
    String user = "root";
    String password = "";
    String driverClass = "com.mysql.jdbc.Driver";
  
    // private constructor
    private ConnectionFactory()
    {
        try {
            Class.forName(driverClass);
        }
        catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
  
    public static ConnectionFactory getInstance()
    {
        return instance;
    }
  
    public Connection getConnection() throws SQLException, ClassNotFoundException
    {
        Connection connection = DriverManager.getConnection(url, user, password);
        return connection;
    }
}

第 4 步：创建一个 Dao 类，用于创建工厂类 Object 并调用该方法。并创建一个查询并将其设置为 JavaBean 对象并添加到 ArrayList 对象。

Java

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
  
public class EmployeeDAO {
  
    Connection connection;
    Statement stmt;
    
    private int noOfRecords;
    public EmployeeDAO() {}
  
    private static Connection getConnection() throws SQLException, ClassNotFoundException
    {
        Connection con = ConnectionFactory.getInstance().getConnection();
        return con;
    }
  
    public List viewAllEmployees(int offset, int noOfRecords)
    {
        String query = "select SQL_CALC_FOUND_ROWS * from employee limit " + offset + ", " + noOfRecords;
        List list = new ArrayList();
        Employee employee = null;
        try {
            connection = getConnection();
            stmt = connection.createStatement();
            ResultSet rs = stmt.executeQuery(query);
            while (rs.next()) {
                employee = new Employee();
                employee.setEmployeeId(rs.getInt(1));
                employee.setEmployeeName(rs.getString(2));
                employee.setSalary(rs.getInt(3));
                employee.setDeptName(rs.getString(4));
                list.add(employee);
            }
  
            rs.close();
            rs = stmt.executeQuery("SELECT FOUND_ROWS()");
  
            if (rs.next())
               this.noOfRecords = rs.getInt(1);
        }
        catch (SQLException e) {
            e.printStackTrace();
        }
        catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        finally
        {
            try {
                if (stmt != null)
                    stmt.close();
                if (connection != null)
                    connection.close();
            }
            catch (SQLException e) {
                e.printStackTrace();
            }
        }
        return list;
    }
    public int getNoOfRecords() { return noOfRecords; }
}

第五步：创建一个Servlet类并创建一个DAO类Object并调用该方法并转发到display.jsp页面

Java

import a1.Employee;
import a1.EmployeeDAO;
import java.io.IOException;
import java.util.List;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
  
public class EmployeeServlet extends HttpServlet {
  
    private static final long serialVersionUID = 1L;
    public EmployeeServlet() { super(); }
  
    @Override
    public void doGet(HttpServletRequest request,
                      HttpServletResponse response)
        throws ServletException, IOException
    {
        int page = 1;
        int recordsPerPage = 5;
        if (request.getParameter("page") != null)
            page = Integer.parseInt(
                request.getParameter("page"));
        EmployeeDAO dao = new EmployeeDAO();
        List list = dao.viewAllEmployees(
            (page - 1) * recordsPerPage,
            recordsPerPage);
        int noOfRecords = dao.getNoOfRecords();
        int noOfPages = (int)Math.ceil(noOfRecords * 1.0
                                       / recordsPerPage);
        request.setAttribute("employeeList", list);
        request.setAttribute("noOfPages", noOfPages);
        request.setAttribute("currentPage", page);
        RequestDispatcher view
            = request.getRequestDispatcher("display.jsp");
        view.forward(request, response);
    }
}

第 6 步：配置 web.xml 文件

XML

  
   
       EmployeeServlet
       a2.EmployeeServlet
   
  
   
       EmployeeServlet
       /employee.do
   
  
   
       30
   
  

第 7 步：创建display.jsp文件以显示 5 到 5 条记录的记录

HTML

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
  
  pageEncoding="ISO-8859-1"%>
  
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
  

  

  




  

  
      
          
          
          
          
      
  
      
          
              
              
              
              
          
      
  
  
Emp ID
Emp Name
Salary
Dept Name
${employee.employeeId}
${employee.employeeName}
${employee.salary}
${employee.deptName}
  
  <%--For displaying Previous link except for the 1st page --%>
  
      Previous
  
  
  <%--For displaying Page numbers. The when condition does not display
              a link for the current page--%>
  
  
      
          
              
                  
                      
                  
                  
                      
                  
              
          
      
  
${i}
${i}
  
  <%--For displaying Next link --%>
  
  
      Next
  
  

  

输出：

Emp Id	Emp Name	Salary	Dp Name
101	Raj	5000	Bca
102	Karan	7000	mca
103	Amit	4000	bcom
104	Manisha	8000	Mba
105	Sakshi	3000	BA

从数据库中获取数百万条记录几乎消耗了机器的所有 CPU 功率和内存。因此，我们将数百万条记录分成小块，每页显示有限数量的记录（比如 5 或 10 条）。