JavaWeb中的分頁技術
阿新 • • 發佈：2018-11-10
前段時間學習SSH框架用到分頁知識，為此還回顧了一下之前JavaWeb中的分頁技術
首先我們先建立一個庫和表用來展示分頁結果
create table Employee(
empId int(11) NOT NULL AUTO_INCREMENT primary key,
empName varchar(20) NOT NULL,
dept_id int(20) NOT NULL
);
insert into Employee(empName,dept_id) values('aa',1);首先我們準備c3p0-config.xml的配置(在ComboPooledDataSource()初始c3p0連線池會載入這裡面的配置資訊，連線具體的資料庫物件)
接下來寫一個連線資料庫的工具類，完成<c3p0-config> <default-config> <property name="jdbcUrl">jdbc:mysql://localhost:3306/jdbc_demo </property> <property name="driverClass">com.mysql.jdbc.Driver</property> <property name="user">root</property> <property name="password">123456</property> <property name="initialPoolSize">3</property> <property name="maxPoolSize">6</property> <property name="maxIdleTime">1000</property> </default-config>
1.初始化資料庫
2.建立DbUtils核心工具類物件QueryRunner
package cn.itcast.utils; import javax.sql.DataSource; import org.apache.commons.dbutils.QueryRunner; import com.mchange.v2.c3p0.ComboPooledDataSource; /** * 工具類 * 1. 初始化C3P0連線池 * 2. 建立DbUtils核心工具類物件 * @author Jie.Yuan * */ public class JdbcUtils { /** * 1. 初始化C3P0連線池 */ private static DataSource dataSource; static { dataSource = new ComboPooledDataSource(); } /** * 2. 建立DbUtils核心工具類物件 */ public static QueryRunner getQueryRuner(){ // 建立QueryRunner物件，傳入連線池物件 // 在建立QueryRunner物件的時候，如果傳入了資料來源物件； // 那麼在使用QueryRunner物件方法的時候，就不需要傳入連線物件； // 會自動從資料來源中獲取連線(不用關閉連線) return new QueryRunner(dataSource); } }
接下來準備實體類，注意由於要用到DbUtils元件，所以實體類中的屬性要與資料庫的欄位一樣
public class Employee {
private int empId; // 員工id
private String empName; // 員工名稱
private int dept_id; // 部門id
public int getEmpId() {
return empId;
}
public void setEmpId(int empId) {
this.empId = empId;
}
public String getEmpName() {
return empName;
}
public void setEmpName(String empName) {
this.empName = empName;
}
public int getDept_id() {
return dept_id;
}
public void setDept_id(int deptId) {
dept_id = deptId;
}
}資料
public class PageBean<T> {
private int currentPage = 1; // 當前頁, 預設顯示第一頁
private int pageCount = 4; // 每頁顯示的行數(查詢返回的行數), 預設每頁顯示4行
private int totalCount; // 總記錄數
private int totalPage; // 總頁數 = 總記錄數 / 每頁顯示的行數 (+ 1)
private List<T> pageData; // 分頁查詢到的資料
public int getCurrentPage() {
return currentPage;
}
public void setCurrentPage(int currentPage) {
this.currentPage = currentPage;
}
public int getPageCount() {
return pageCount;
}
public void setPageCount(int pageCount) {
this.pageCount = pageCount;
}
public int getTotalCount() {
return totalCount;
}
public void setTotalCount(int totalCount) {
this.totalCount = totalCount;
}
public int getTotalPage() {
if(totalCount%pageCount==0){
this.totalCount=totalCount%pageCount;
}else{
this.totalCount=totalCount%pageCount+1;
}
return totalPage;
}
public void setTotalPage(int totalPage) {
this.totalPage = totalPage;
}
public List<T> getPageData() {
return pageData;
}
public void setPageData(List<T> pageData) {
this.pageData = pageData;
}
}public interface UserDao {
public int getTotalCount();
public void getPageData(PageBean<Employee> pb);
}在sql語句中的分頁語句是select * from 表 limt ?,?分別是查詢的起始行和查詢的行數
package cn.itcast.dao.impl;
import java.sql.SQLException;
import java.util.List;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanListHandler;
import org.apache.commons.dbutils.handlers.ScalarHandler;
import cn.itcast.dao.UserDao;
import cn.itcast.entity.Employee;
import cn.itcast.utils.JdbcUtils;
import cn.itcast.utils.PageBean;
public class UserDaoImpl implements UserDao{
@Override
public int getTotalCount() {
String sql="select count(*) from Employee";
try {
QueryRunner qr = JdbcUtils.getQueryRuner();
Long count=qr.query(sql, new ScalarHandler<Long>());
return count.intValue();
} catch (SQLException e) {
throw new RuntimeException(e);
}
}
@Override
public void getPageData(PageBean<Employee> pb) {
int totalCount=getTotalCount();
pb.setTotalCount(totalCount);
if(pb.getCurrentPage()<1){
pb.setCurrentPage(1);
}else if(pb.getCurrentPage()>pb.getTotalPage()){
pb.setCurrentPage(pb.getTotalPage());
}
try {
int first=(pb.getCurrentPage()-1)*pb.getPageCount();
int count=pb.getPageCount();
String sql="select * from Employee limit ?,?";
QueryRunner qr = JdbcUtils.getQueryRuner();
List<Employee> list=qr.query(sql, new BeanListHandler<Employee>(Employee.class),first,count);
pb.setPageData(list);
} catch (SQLException e) {
// TODO Auto-generated catch block
throw new RuntimeException(e);
}
}
}
package cn.itcast.service;
import cn.itcast.entity.Employee;
import cn.itcast.utils.PageBean;
public interface IEmployeeService {
public void getAll(PageBean<Employee> pb);
}
public class UserDaoService implements IEmployeeService{
private UserDao userDao = new UserDaoImpl();
public void getAll(PageBean<Employee> pb) {
userDao.getPageData(pb);
}
}public class IndexServlet extends HttpServlet {
// 建立Service例項
private IEmployeeService employeeService = new EmployeeService();
// 跳轉資源
private String uri;
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
try {
//1. 獲取“當前頁”引數； (第一次訪問當前頁為null)
String currPage = request.getParameter("currentPage");
// 判斷
if (currPage == null || "".equals(currPage.trim())){
currPage = "1"; // 第一次訪問，設定當前頁為1;
}
// 轉換
int currentPage = Integer.parseInt(currPage);
//2. 建立PageBean物件，設定當前頁引數； 傳入service方法引數
PageBean<Employee> pageBean = new PageBean<Employee>();
pageBean.setCurrentPage(currentPage);
//3. 呼叫service
employeeService.getAll(pageBean); // 【pageBean已經被dao填充了資料】
//4. 儲存pageBean物件，到request域中
request.setAttribute("pageBean", pageBean);
//5. 跳轉
uri = "/WEB-INF/list.jsp";
} catch (Exception e) {
e.printStackTrace(); // 測試使用
// 出現錯誤，跳轉到錯誤頁面；給使用者友好提示
uri = "/error/error.jsp";
}
request.getRequestDispatcher(uri).forward(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
this.doGet(request, response);
}
}<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!-- 引入jstl核心標籤庫 -->
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>分頁查詢資料</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
</head>
<body>
<table border="1" width="80%" align="center" cellpadding="5" cellspacing="0">
<tr>
<td>序號</td>
<td>員工編號</td>
<td>員工姓名</td>
</tr>
<!-- 迭代資料 -->
<c:choose>
<c:when test="${not empty requestScope.pageBean.pageData}">
<c:forEach var="emp" items="${requestScope.pageBean.pageData}" varStatus="vs">
<tr>
<td>${vs.count }</td>
<td>${emp.empId }</td>
<td>${emp.empName }</td>
</tr>
</c:forEach>
</c:when>
<c:otherwise>
<tr>
<td colspan="3">對不起，沒有你要找的資料</td>
</tr>
</c:otherwise>
</c:choose>
<tr>
<td colspan="3" align="center">
當前${requestScope.pageBean.currentPage }/${requestScope.pageBean.totalPage }頁
<a href="${pageContext.request.contextPath }/index?currentPage=1">首頁</a>
<a href="${pageContext.request.contextPath }/index?currentPage=${requestScope.pageBean.currentPage-1}">上一頁 </a>
<a href="${pageContext.request.contextPath }/index?currentPage=${requestScope.pageBean.currentPage+1}">下一頁 </a>
<a href="${pageContext.request.contextPath }/index?currentPage=${requestScope.pageBean.totalPage}">末頁</a>
</td>
</tr>
</table>
</body>
</html>