简单分页实现（底层）

目的：实现分页

效果：
实现步骤：

1.搭建mybatis

1.1导入jar包

mybatis-3.4.1.jar
mysql-connector-java-5.1.38.jar
（记得buildPath）

1.2连接数据库

资源文件下建两个配置文件
db.properties存放连接数据库的信息

driverClassName=com.mysql.jdbc.Driver
url=jdbc:mysql:///student?characterEncoding=UTF-8&useSSL=true&serverTimezone=UTC
username=root
password=root

Mybatis-config.xml 为主配置文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration
  PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
  "http://mybatis.org/dtd/mybatis-3-config.dtd">
	<configuration>
	<properties resource="db.properties"></properties>
		<!-- <typeAliases>
			<typeAlias alias="" type="" />
		</typeAliases> -->
		
		<environments default="development">
			<environment id="development">
				<transactionManager type="JDBC"	/>
				<!-- 读取数据库连接的信息 -->
				<dataSource type="POOLED">
					<property name="driver" value="${driverClassName}" />
					<property name="url" value="${url}" />
					<property name="username" value="${username}" />
					<property name="password" value="${password}" />
				</dataSource>
			</environment>
		</environments>
		<!-- 加载XXXMapper.xml配置文件 -->
		<mappers>
			<mapper resource="cn/wolfcode/mapper/StudentMapper.xml" />
		</mappers>
	</configuration>

写一个工具类用于获取数据库连接

/**
 * 
 * @author 红烛
 *
 */
public class MybatisUtil {
	private static SqlSessionFactory factory;
	
	private MybatisUtil(){};
	
	static{
		try {
			factory=new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("Mybatis-config.xml"));
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
	
	public static SqlSession getSession(){
		SqlSession session=factory.openSession();
		return session;
	}
}

2.封装sql查询所需的参数为对象

QueryObject类中存放了sql语句查询所需参数

private int currentPage=PageContant.CURRENT_PAGE;

@Getter
@Setter
public class QueryObject {
  	/**
	 * 默认初始页
	 */	
	private int currentPage=1;
    /**
	 * 每页显示的数据条数
	 */
	private int pageSize=3;
	/**
	*SQL语句中的参数是通过get方法拿到属性的，beginIndex表示当前页第一条数据的索引
	**/
	public int getBeginIndex(){
		return (this.currentPage-1)*this.pageSize;
	}
}

3封装分页相关参数

PageResult类中封装了分页的相关数据

  @Getter
    @Setter
    public class PageResult {
    	private int currentPage=PageContant.CURRENT_PAGE;
    	private int pageSize=PageContant.PAGE_SIZE;
    	private int totalCount;
    	private int totalPage;
    	private int prevPage;
    	private int nextPage;
    	private List<Student> listDate;
    	/**
    	*少参构造器调多参构造器，当没有数据时只需要调这两个参数的构造器就可以没必要调4个参数的
    	*new ArrayList<Student>() 这样写是因为jsp页面使用<c:forEach>遍历的集合不能空，否则会报空指针异常
    	* 这样写可在没有数据时也不报异常
    	**/
    	public PageResult(int currentPage,int pageSize){
    		this(currentPage, pageSize, new ArrayList<Student>(), 0);
    	}
    
    	public PageResult(int currentPage, int pageSize, List<Student> listDate, int totalCount) {
	    	/**
	    	*当前页
	    	**/
    		this.currentPage = currentPage;
    		/**
	    	*每页显示的数据条数
	    	**/
    		this.pageSize = pageSize;
    		/**
	    	*当前页的数据集合
	    	**/
    		this.listDate = listDate;
    		/**
	    	*数据的总条数
	    	**/
    		this.totalCount = totalCount;
    		/**
	    	*总页数
	    	**/
    		this.totalPage=this.totalCount % this.pageSize==0
    				?this.totalCount / this.pageSize
    				:this.totalCount / this.pageSize+1;
    		/**
	    	*前一页
	    	**/
    		this.prevPage=this.currentPage-1>1?this.currentPage-1:1;
    		/**
	    	*下一页
	    	**/
    		this.nextPage=this.currentPage+1<this.totalPage
    				?this.currentPage+1
    				:this.totalPage;
    	}
    }

4.StudentMapper.xml

StudentMapper接口中什么都不用写，将方法写到dao层接口中，当然写没问题

<!-- 得到当前页结果集 -->
<select id="queryForList" resultType="cn.wolfcode.domain.Student">
	select * from student 
	limit #{beginIndex},#{pageSize}
</select>

<!-- 得到数据总个数 -->
<select id="queryForCount" resultType="int">
	select count(*) from student
</select>

5.dao层实现

IStudentDAO

/**
 * 
 * @author 红烛
 *
 */
public interface IStudentDAO {
	/**
	 * 查询结果集
	 * @return
	 */
	List<Student> queryForList(QueryObject qo);
	/**
	 * 查询数据数量
	 * @return
	 */
	int queryForCount(QueryObject qo);	
}

StudentDAOImpl 接口实现

@Override
	public List<Student> queryForList(QueryObject qo) {
		SqlSession session=MybatisUtil.getSession();
		List<Student> list=session.selectList("cn.wolfcode.mapper.StudentMapper.queryForList",qo);
		session.commit();
		session.close();
		return list;
	}

	@Override
	public int queryForCount(QueryObject qo) {
		SqlSession session=MybatisUtil.getSession();
		int  totalCount=session.selectOne("cn.wolfcode.mapper.StudentMapper.queryForCount",qo);
		session.commit();
		session.close();
		return totalCount;
	}

6.service层实现

IStudentService 接口

/**
 * 
 * @author 红烛
 *
 */
public interface IStudentService {
	/**
	 * 分页所有结果
	 * @param qo
	 * @return
	 */
	PageResult query(QueryObject qo);
}

IStudentService 接口实现

/**
 * 
 * @author 红烛
 *
 */
public class StudentServiceImpl implements IStudentService {
	private IStudentDAO dao = new StudentDAOImpl();

	@Override
	public PageResult query(StudentQueryObject qo) {
		int totalCount = dao.queryForCount(qo);
		if (totalCount == 0) {
		//如果没有数据调用两个参数的构造器
			return new PageResult(qo.getCurrentPage(), qo.getPageSize());
		}
		List<Student> listDate = dao.queryForList(qo);
		return new PageResult(qo.getCurrentPage(), qo.getPageSize(), listDate, totalCount);
	}
}

7.servlet实现

/**
 * 
 * @author 红烛
 *
 */
@WebServlet("/student")
public class StudentServlet extends HttpServlet{
	
	private IStudentService studentService=new StudentServiceImpl();

	private static final long serialVersionUID = 1L;

	@Override
	protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
	    QueryObject qo=new QueryObject();
		req2stu(request, qo);
		PageResult result=studentService.query(qo);
		request.setAttribute("result", result);
		//跳转到主页·list.jsp
		request.getRequestDispatcher("/WEB-INF/view/list.jsp").forward(request, response);
	}
	
	//接收jsp页面数据封装成对象	
	protected void req2stu(HttpServletRequest request, QueryObject qo) {
		String currentPage=request.getParameter("currentPage");
		String pageSize=request.getParameter("pageSize");
		if(StringUtil.hasLength(currentPage)){
			qo.setCurrentPage(Integer.valueOf(currentPage));
		}
		if(StringUtil.hasLength(pageSize)){
			qo.setPageSize(Integer.valueOf(pageSize));
		}
	}
}

8.jsp页面

  <%@ page language="java" contentType="text/html; charset=UTF-8"
    	pageEncoding="UTF-8"%>
    <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
    <%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt"%>
    <html>
    <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>学生信息页</title>
    <!--点击上一页下一页首页尾页时实现表单的提交，不然没有翻页效果-->
    <script type="text/javascript">
	funtion submitForm(pageNum){
		document.getElementById("currentPage").value=pageNum;
		//forms[0]表示提交的是本页面的第一个表单
		document.forms[0].submit();
	}
</script>
    </head>
    <body>
    	<div>
    		<table border="1" cellspacing="0" cellpadding="0">
    			<thead>
    				<tr>
    					<td>编号</td>
    					<td>姓名</td>
    					<td>年龄</td>
    					<td>生日</td>
    					<td>地址</td>
    					<td>电话</td>
    					<td>邮箱</td>
    				</tr>
    			</thead>
    			<tbody>
    				<c:forEach var="stu" items="${result.listDate}">
    					<tr>
    						<td>${stu.id}</td>
    						<td>${stu.name}</td>
    						<td>${stu.age}</td>
    					<!-- type="date"或是 type="both" 都可以实现日期格式化--> 
    						<td><fmt:formatDate pattern="yyyy-MM-dd"
    								value="${stu.birthday}" type="date" /></td>
    						<td>${stu.address}</td>
    						<td>${stu.phone}</td>
    						<td>${stu.email}</td>
    					</tr>
    				</c:forEach>
    			</tbody>
    				<tfoot>
    				<tr>
    					<td colspan="8">
    						<a href="javaScript:submitForm(1)">首页</a>
    						<a href="javaScript:submitForm(${result.prevPage})">上一页</a>
    						<a href="javaScript:submitForm(${result.nextPage})">下一页</a>
    						<a href="javaScript:submitForm(${result.totalPage})">尾页</a>
    					      共${result.totalCount}条数据
    					      页码${result.currentPage}/${result.totalPage}页 
    					      每页显示
    					      <select name="pageSize">
    					      	<option ${result.pageSize==3 ? 'selected' : ''}>3</option>
    					      	<option ${result.pageSize==5 ? 'selected' : ''}>5</option>
    					      	<option ${result.pageSize==7 ? 'selected' : ''}>7</option>
    					      </select>
    					      条数据  
    					      跳转至
    					   <input type="text" name="currentPage" id="currentPage" value="${result.currentPage}"/>页
    					   <input type="submit" value="GO"/>
    					</td>
    				</tr>
    			</tfoot>
    		</table>
    	</div>
    </body>
    </html>

9.启动服务器测试一下