分页查询在我们生活中非常常见,当我们做一个内容很多,数据量很大的项目的时候,在一个页面显示不过来,我们便会采取分页的思想,在每个页面上显示固定数量的内容,分多个页面显示。那它是怎么实现的呢?今天我们来讲讲如何用MyBatis来实现分页查询。
假设我们要查找的是学生信息,然后将信息分页显示到jsp页面上,首先我们要做的是写实体类,创建一个名为pojo的包,在包下写一个People类,定义属性和对应的set/get方法。
package edu.swpu.pojo;
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 + "]";
}
}
其次写MyBatis的全局配置文件,在src下创建mybatis.xml文件,定义别名,写数据库连接的配置信息以及要扫描的对应的Mapper.xml文件的路径。
<?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>
<typeAliases>
<package name="edu.swpu.pojo"/>
</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="1234"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="edu/swpu/mapper/PeopleMapper.xml"/>
</mappers>
</configuration>
然后创建一个名为mapper的包,在包下创建PeopleMapper.xml文件,先写用于查询的sql语句,resultType属性定义范围值类型为people,使用parameterType属性来传递分页查询需要的两个参数。
<?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">
<mapper namespace="edu.swpu.mapper.PeopleMapper">
<select id="selByPage" resultType="people" parameterType="map">
select * from people limit #{pageStart},#{pageSize}
</select>
<select id="selCount" resultType="long">
select count(*) from people
</select>
</mapper>
然后封装一个专门分页的类PageInfo,封装页面的尺寸pageSize,当前第几页pageNumber,总页数total和当前页显示的数据list。
package edu.swpu.pojo;
import java.util.List;
public class PageInfo {
//每页显示个数
private int pageSize;
//当前第几页
private int pageNumber;
//总页数
private long total;
//当前页显示的数据
private List<?> list;
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;
}
}
接下来就可以写service了,先创建service包,定义PeopleService接口,定义用来显示数据的showPage(int pageSize,int pageNumber)方法。
package edu.swpu.service;
import java.io.IOException;
import edu.swpu.pojo.PageInfo;
public interface PeopleService {
/**
* 分页显示
* @param pageSize
* @param pageNumber
* @return
*/
PageInfo showPage(int pageSize,int pageNumber) throws IOException;
}
再在service包下创建impl包,编写PeopleService的实现类PeopleServiceImpl,实现showPage(int pageSize,int pageNumber)方法。先根据MyBatis的语法规则创建用于查询的SqlSession对象,再创建一个pageInfo对象,将传来的参数值传递给pageInfo对象对应的属性,再定义一个HashMap,将查询需要的参数封装到map中,传给写好的sql语句,此处sql语句需要的两个参数是pageStart和pageSize,pageSize就是showPage方法的参数,但是pageStart需要我们运算一下,pageStart=pageSize*(pageNumber-1),最后,session打点调selectList方法并将查到的数据放到pageInfo对象的list属性中,返回pageInfo对象。
package edu.swpu.service.impl;
import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.Map;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import edu.swpu.pojo.PageInfo;
import edu.swpu.service.PeopleService;
public class PeopleServiceImpl implements PeopleService {
@Override
public PageInfo showPage(int pageSize, int pageNumber) throws IOException {
InputStream is = Resources.getResourceAsStream("mybatis.xml");
SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(is);
SqlSession session = factory.openSession();
PageInfo pi = new PageInfo();
pi.setPageNumber(pageNumber);
pi.setPageSize(pageSize);
Map<String,Object> map =new HashMap<>();
map.put("pageStart",pageSize*(pageNumber-1));
map.put("pageSize", pageSize);
pi.setList(session.selectList("edu.swpu.mapper.PeopleMapper.selByPage",map));
//总条数
long count = session.selectOne("edu.swpu.mapper.PeopleMapper.selCount");
pi.setTotal(count%pageSize==0?count/pageSize:count/pageSize+1);
return pi;
}
}
接下来该写servlet了,创建一个servlet包,在servlet包下创建showPageServlet类,继承HttpServlet类,重写service方法,先创建PeopleService对象。因为你无法知道用户是不是第一访问这个页面,所以我们应该在service中加入/第一次访问的验证,如果没有传递参数,设置默认值,再调用showPage()方法,将返回的pageInfo对象放入request对象中,调用getRequestDispatcher()方法将请求转发到jsp页面。
package edu.swpu.servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import edu.swpu.pojo.PageInfo;
import edu.swpu.service.PeopleService;
import edu.swpu.service.impl.PeopleServiceImpl;
@WebServlet("/page")
public class ShowPageServlet extends HttpServlet{
private PeopleService peopleService = new 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;
if(pageSizeStr!=null&&!pageSizeStr.equals("")){
pageSize = Integer.parseInt(pageSizeStr);
}
String pageNumberStr = req.getParameter("pageNumber");
int pageNumber = 1;
if(pageNumberStr!=null&&!pageNumberStr.equals("")){
pageNumber = Integer.parseInt(pageNumberStr);
}
PageInfo pi = peopleService.showPage(pageSize, pageNumber);
req.setAttribute("PageInfo", pi);
req.getRequestDispatcher("index.jsp").forward(req, resp);
}
}
最后创建jsp页面来显示数据。
<%@ 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>
<a href="page?pageNumber=${PageInfo.pageNumber-1 }&pageSize=${PageInfo.pageSize}" <c:if test="${PageInfo.pageNumber<=1 }"> οnclick="javascript:return false;" </c:if> >上一页</a>
<a href="page?pageNumber=${PageInfo.pageNumber+1 }&pageSize=${PageInfo.pageSize}" <c:if test="${PageInfo.pageNumber>=PageInfo.total }"> οnclick="javascript:return false;" </c:if> >下一页</a>
</body>
</html>