MyBatis_6

1.MyBatis的分页
通过分页插件来完成对数据库表记录的分页查询。
在javaWEB的学习过程中，使用JDBC的方式实现过关于数据的分页，主要实现的原理：
在查询的语句后面添加limit关键字，然后实现查询的数据分页功能。但是如果需要在所有的查询中都添加分页的话，那么就需要在所有的select语句后面添加limit关键字，这样的工作量是巨大的。同时也要改动大量的代码。
mybatis中提供的插件（plugin）机制，运行在mybatis的原有的处理逻辑上添加一些额外的逻辑，这样既不需要修改原来的代码，而且还可以非常容易进行实现。
mybatis的插件机制，本质就拦截指定的查询操作，然后在查询的操作添加相关的分页逻辑。
使用PageHelper实现分页
1.创建数据库表

#用户基本信息
create database lianxi;
use lianxi;
create table t_user(
user_id int primary key auto_increment,
user_name varchar(20),
user_age int,
user_address varchar(30)
);

2.创建项目
3.修改项目结构
4.Pom.xml配置依赖

<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
<dependency>
  <groupId>mysql</groupId>
  <artifactId>mysql-connector-java</artifactId>
  <version>5.1.38</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
<dependency>
  <groupId>org.mybatis</groupId>
  <artifactId>mybatis</artifactId>
  <version>3.4.6</version>
</dependency>
<!-- 配置分页依赖 -->
<!-- https://mvnrepository.com/artifact/com.github.pagehelper/pagehelper -->
<dependency>
  <groupId>com.github.pagehelper</groupId>
  <artifactId>pagehelper</artifactId>
  <version>5.1.2</version>
</dependency>

5.创建javabean

package com.wangxing.mybatis.bean;

public class UserBean {
    private int userid;
    private String username;
    private int userage;
    private String useraddress;

    public int getUserid() {
        return userid;
    }

    public void setUserid(int userid) {
        this.userid = userid;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public int getUserage() {
        return userage;
    }

    public void setUserage(int userage) {
        this.userage = userage;
    }

    public String getUseraddress() {
        return useraddress;
    }

    public void setUseraddress(String useraddress) {
        this.useraddress = useraddress;
    }
}

6.创建数据访问接口

package com.wangxing.mybatis.mapper;

import com.wangxing.mybatis.bean.UserBean;

import java.util.List;

public interface UserMapper {
    public void insertUser(List<UserBean>userBeanList);
    public List<UserBean>selectUser();
}

7.SQL映射文件

<?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="com.wangxing.mybatis.mapper.UserMapper">
    <insert id="insertUser" parameterType="java.util.List">
        insert into t_user values
        <foreach collection="list" item="person" separator=",">
         (null,#{person.username},#{person.userage},#{person.useraddress})
        </foreach>

    </insert>
    <resultMap id="userMap" type="com.wangxing.mybatis.bean.UserBean">
        <id column="user_id" property="userid"></id>
        <result column="user_name" property="username"></result>
        <result column="user_age" property="userage"></result>
        <result column="user_address" property="useraddress"></result>
    </resultMap>
    <select id="selectUser" resultMap="userMap">
        select * from t_user
    </select>
</mapper>

8.创建核心配置文件

<!-- 配置分页插件的拦截器 -->
   <plugins>
      <plugin interceptor="com.github.pagehelper.PageInterceptor">
			<!-- 配置方言，使用的是那个库  ，在PageHelper5.0之后 不需要配置-->
			<!--  <property name="dialect" value="mysql"/> -->
		</plugin>
   </plugins>

9.测试代码

package com.wangxing.mybatis.test;
import com.github.pagehelper.Page;
import com.github.pagehelper.PageHelper;
import com.github.pagehelper.PageInfo;
import com.wangxing.mybatis.bean.UserBean;
import com.wangxing.mybatis.mapper.UserMapper;
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 javax.jws.soap.SOAPBinding;
import java.util.ArrayList;
import java.util.List;
public class TestMain {
    //得到Sqlsession对象
    public static SqlSession getSession() throws Exception{
        SqlSession sqlSession = null;
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config.xml"));
        return sqlSessionFactory.openSession();
    }
    //得到添加到数据库表中的数据集合
    public static List<UserBean>getData(){
        List<UserBean>userBeanList=new ArrayList<UserBean>();
        for(int i=1;i<=100;i++){
            UserBean userBean=new UserBean();
            userBean.setUsername("zhangsan-"+i);
            userBean.setUserage(20+i);
            userBean.setUseraddress("xian-"+i);
            userBeanList.add(userBean);
        }
        return userBeanList;
    }
    //批量添加数据
    public static void testInsert(){
        SqlSession sqlSession=null;
        try {
            sqlSession = getSession();
            UserMapper userMapper=sqlSession.getMapper(UserMapper.class);
            userMapper.insertUser(getData());
            sqlSession.commit();
        }catch (Exception e){
            e.printStackTrace();
            sqlSession.rollback();
        }finally {
            sqlSession.close();
        }
    }
    //测试分页查询
    public static  void testSelectPage(){
        SqlSession sqlSession=null;
        try{
            sqlSession=getSession();
            UserMapper userMapper=sqlSession.getMapper(UserMapper.class);
            //设置分页参数
            //设置分页的起始页码和每页的显示数据的行数
            PageHelper.startPage(2,10);
            List<UserBean> userBeanList=userMapper.selectUser();
            PageInfo<UserBean> pageInfo=new PageInfo<UserBean>(userBeanList);
            //Page<UserBean>page=(Page<UserBean>)userBeanList;
            sqlSession.commit();
            System.out.println("当前页=="+pageInfo.getPageNum());
            System.out.println("每页数量=="+pageInfo.getPageSize());
            System.out.println("当前页的数量"+pageInfo.getSize());
            System.out.println("总记录数=="+pageInfo.getTotal());
            System.out.println("总页面=="+pageInfo.getPages());
            //得到当前页的结果集合
            List<UserBean>userlist=pageInfo.getList();
            for(UserBean userBean:userlist){
                System.out.println(userBean.getUserid()+" "+userBean.getUsername());
            }
        }catch(Exception e){
            e.printStackTrace();

        }finally {
            sqlSession.close();
        }
    }
    public static void main(String[] args) {
       // testInsert();
        testSelectPage();
    }
}

运行结果