2020-03-25

Mybatis实现分页功能（完整流程）

Mybatis实现分页功能

准备数据库

实体类 People

public class People {
	private int id;
	private String name;
	private int age;
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	@Override
	public String toString() {
		return "People [id=" + id + ", name=" + name + ", age=" + age + "]";
	}
}

导入相关jar包

全局配置文件mybatis.xml

<?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">   <!--dtd文件  约束(chm文件可以找到)-->

<configuration>

	<typeAliases>
		<package name="com.bjsxt.pojo"/>   <!-- 起别名  方便在配置的xml里面直接返回值就可以只写类名-->
	</typeAliases>
	
	<environments default="default">
		<environment id="default">
			<transactionManager type="JDBC"></transactionManager>
			<dataSource type="POOLED">
				<property name="driver" value="com.mysql.jdbc.Driver"/>
				<property name="url" value="jdbc:mysql://localhost:3306/ssm"/>
				<property name="username" value="root"/>
				<property name="password" value="njdxrjgc7777777."/>
			</dataSource>
		</environment>
	</environments>
	
	<mappers>
		<mapper resource="com/bjsxt/mapper/PeopleMapper.xml"/>  <!-- 直接调用配置文件  执行sql语句 -->
	</mappers>
	
</configuration>

配置PeopleMapper.xml

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE mapper
  PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  "http://mybatis.org/dtd/mybatis-3-mapper.dtd">   <!--dtd文件  约束(chm文件可以找到)-->

  <mapper namespace="com.bjsxt.mapper.PeopleMapper" >     <!-- 确定这个mapper名字： 包.类名 -->
	<select id="selByPage" resultType="People" parameterType="map">     <!-- 确定方法叫selByPage 返回值给people实体类 传入参数的类型是map -->
			select * from people limit #{pageStart},#{pageSize};        <!-- limit 后面通过#{}方式传入两个map参数-->
	</select>
  </mapper>

构建实体类pageInfo用于传递分层相关的参数


public class PageInfo {

	private int pageSize;  //一页分布几个
	private int pageNumber;  //第几页
	private long total;   //一共总页数 分多少页
	private List<?> list;   //当前页显示哪些数据 
		
	public int getPageSize() {
		return pageSize;
	}
	public void setPageSize(int pageSize) {
		this.pageSize = pageSize;
	}
	public int getPageNumber() {
		return pageNumber;
	}
	public void setPageNumber(int pageNumber) {
		this.pageNumber = pageNumber;
	}
	public long getTotal() {
		return total;
	}
	public void setTotal(long total) {
		this.total = total;
	}
	public List<?> getList() {
		return list;
	}
	public void setList(List<?> list) {
		this.list = list;
	}
	
}

service和实现层

service层实现代码:

public interface PeopleService {
	//实现分页展示  传入两个参数
	PageInfo showPage(int pageSize,int pageNumber) throws IOException;
}

serviceimpl层实现代码:

public class PeopleServiceImpl implements PeopleService {
	
	@Override
	public PageInfo showPage(int pageSize, int pageNumber) throws IOException {
		
		//获取配置资源
			InputStream is = Resources.getResourceAsStream("mybatis.xml");
		
		//使用构建者模式(加快工厂实例化)和工厂模式生产session
			SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(is);
				SqlSession session = factory.openSession();
	
		//创建对象
		    PageInfo pi=new PageInfo(); 
				pi.setPageNumber(pageNumber);
				pi.setPageSize(pageSize);
		
		//新建map对象  
		Map<String,Object> map=new HashMap<>();
			map.put("pageStart",pageSize*(pageNumber-1));  //设置好每一页开始的那个数字
			map.put("pageSize",pageSize);  //设置好每一页有几个
			pi.setList(session.selectList("com.bjsxt.mapper.PeopleMapper.selByPage",map));  //要设置返回结果  第二个参数是传入两个key值
		 
		//总条数
			long count=session.selectOne("com.bjsxt.mapper.PeopleMapper.selCount");  //获取查询总条数
			
			pi.setTotal(count%pageSize==0?count/pageSize:count/pageSize+1);  //要设置总共几页  总数/每一页  
		
		return pi;
	}

}

因为要获得所有数count 要在xml配一个查询所有的select标签

1
2
3

<select id="selCount" resultType="Long">
	select count(*) from people
</select>

Servlet类

@WebServlet("/page")  //使用注解的方式 最后要在web里面写/page才可以

public class ShowPageServlet extends HttpServlet{
		
	//面向接口编程
	private	PeopleService peopleService=new com.bjsxt.serviceimpl.PeopleServiceImpl();
	
	@Override
	protected void service(HttpServletRequest req,HttpServletResponse resp)throws ServletException,IOException{
		
		//第一次访问的验证 如果没有传递参数 设置默认值
		String  pageSizeStr = req.getParameter("pageSize");
		int pageSize=2;  //一页显示几个
		if(pageSizeStr!=null&&!pageSizeStr.equals(""))
		{
			pageSize = Integer.parseInt(pageSizeStr);     //获取两个参数
		}
		
		String pageNumberStr = req.getParameter("pageNumber");
		int pageNumber = 1; //显示第几页
		if(pageNumberStr!=null&&!pageNumberStr.equals(""))
		{
			pageNumber = Integer.parseInt(pageNumberStr);  //获取两个参数
		}
		
		PageInfo pi=peopleService.showPage(pageSize, pageNumber);   //分页展示效果给了pageinfo实体类
		
		//  传过去
			req.setAttribute("PageInfo", pi);
		
		//  请求转发
			req.getRequestDispatcher("index.jsp").forward(req, resp);
	
	}
	
}

index.jsp页面

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
 <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
	<table border="1">
		<tr>
			<th>编号</th>
			<th>姓名</th>
			<th>年龄</th>
		</tr>
		<c:forEach items="${PageInfo.list }" var="pi">    
			<tr>
				<td>${pi.id }</td>
				<td>${pi.name }</td>
				<td>${pi.age }</td>
			</tr>
		</c:forEach>
	</table>
	
	<!-- 跳转通过onclick点击事件 然后js的行内表达方式 取消跳转等功能 c:if进行判断 -->
		<a href="page?pageNumber=${PageInfo.pageNumber-1 }&pageSize=${PageInfo.pageSize}" <c:if test="${PageInfo.pageNumber<=1 }">  onclick="javascript:return false;" </c:if> >上一页</a>
		<a href="page?pageNumber=${PageInfo.pageNumber+1 }&pageSize=${PageInfo.pageSize}" <c:if test="${PageInfo.pageNumber>=PageInfo.total }">  onclick="javascript:return false;" </c:if> >下一页</a>

</body>
</html>