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Mybatis学习笔记第一天

文章目录

Mybatis

环境:

  • JDK1.8
  • Mysql5.7
  • maven3.6.1
  • IDEA

1.简介

1.1什么是Mybatis

  • MyBatis 是一款优秀的持久层框架
  • 它支持自定义 SQL、存储过程以及高级映射。
  • MyBatis 免除了几乎所有的 JDBC 代码以及设置参数和获取结果集的工作。
  • MyBatis 可以通过简单的 XML 或注解来配置和映射原始类型、接口和 Java POJO(Plain Old Java Objects,普通老式 Java 对象)为数据库中的记录。
  • MyBatis本是apache的一个开源项目iBatis,2010年这个项目由apache software foundation迁移到了[google code](https://baike.baidu.com/item/google code/2346604),并且改名为MyBatis。
  • 2013年11月迁移到Github。

如何获得Mybatis?

  • maven仓库
  • Github

1.2、持久化

数据持久化

  • 持久化就是将程序的数据在持久状态和瞬间状态转化的过程
  • 持久化:将数据保存到数据库,文档
  • 瞬间状态:数据保存在内存,断电即失

1.3持久层

Dao层、Service层、Controller层。。。。

  • 完成持久化工作的代码块
  • 层界限十分明显。

1.4为什么需要Mybatis?

  • 方便

  • 传统的JDBC代码太复杂了,简化代码,框架、自动化。

  • 帮助将数据存到数据库中

2.第一个Mybatis程序

思路:搭建环境–>导入Mybatis—>编写代码–>测试!

2.1、搭建环境

搭建数据库

CREATE DATABASE `Mybatis`

CREATE TABLE `user`

INSERT INTO `user`(id ,`name`,pwd) VALUES
(1001,'曹久平','123456'),
(1002,'张三','1234'),
(1003,'李四','12345')

新建项目

1、新建一个普通的maven项目

2、删除src目录

3、导入maven依赖

<dependencies>
<!--    mysql驱动-->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.47</version>
    </dependency>
<!--    mybatis-->
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.2</version>
    </dependency>
<!--    junit-->
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
        <scope>test</scope>
    </dependency>
</dependencies>

2.2、创建一个模块

  • 新建一个mybatis核心配置文件
<?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">
<!--核心配置文件-->
<configuration>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
</configuration>
  • 编写mybatis工具类
public class MybatisUtil {
    private static SqlSessionFactory sqlSessionFactory;
    static {
        try {
            //使用Mybatis的第一步,获取SqlSessionFactory对象
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }
}

2.3、编写代码

  • 实体类
package com.cjp.pojo;

//实体类
public class User {
    private int id;
    private  String name;
    private String pwd;

    public User() {
    }

    public User(int id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }

    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 String getPwd() {
        return pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", pwd='" + pwd + '\'' +
                '}';
    }
}
 
  • Dao接口
package com.cjp.dao;

import com.cjp.pojo.User;

import java.util.List;

public interface UserDao {
    List<User> getUserList();
}

  • 接口实现类(由于原来的一个实现类转化为一个Mapper配置文件)
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--namespace=绑定一个对应的Dao、Mapper接口-->
<mapper namespace="com.cjp.dao.UserDao">
    <!--查询语句-->
    <select id="getUserList" resultType="com.cjp.pojo.User">
        select * from mybatis.user
    </select>
</mapper>

2.3、测试

注意:maven导出资源问题:

 <build>
        <resources>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>false</filtering>
            </resource>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>false</filtering>
            </resource>
        </resources>
    </build>
package com.cjp.dao;

import com.cjp.pojo.User;
import com.cjp.utils.MybatisUtil;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class UserDaoTest {
    @Test
    public void test() {
        //第一步,获得SqlSession对象
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        try {
            //第二步,执行sql
            //方式一:
            UserDao mapper = sqlSession.getMapper(UserDao.class);
            List<User> userList = mapper.getUserList();
            for (User user : userList) {
                System.out.println(user);
            }
            /*//方式二:(不推荐使用)
        List<User> users = sqlSession.selectList("com.cjp.dao.UserDao.getUserList");
        for (User user : users) {
            System.out.println(user);
        }*/
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            //关闭SqlSession
            sqlSession.close();
        }
    }
}

3.CRUD

1.namespace

namespace中的包名要和Dao/Mapper接口的包名一致

2.select

查询语句

  • id:就是对应的namespace中的方法名;
  • resultType:sql语句执行返回值;
  • parameterType:参数

3.增删改查实现

在之前基础上,增删改查只需要更新UserMapper接口中的方法、UserMapper.xml中的配置、以及测试代码即可。

注意:增删改需要提交事务

UserMapper:

package com.cjp.dao;

import com.cjp.pojo.User;

import java.util.List;

public interface UserMapper {
    //获取全部用户
    List<User> getUserList();
    //根据id查询用户
    User getUserById(int id);
    //添加一个用户
    int insertUser(User user);
    //修改用户
    int updateUser(User user);
    //删除用户
    int deleteUser(int id);
}

UserMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--namespace=绑定一个对应的Dao、Mapper接口-->
<mapper namespace="com.cjp.dao.UserMapper">
    <!--查询语句-->
    <select id="getUserList" resultType="com.cjp.pojo.User">
        select * from mybatis.user
    </select>

    <select id="getUserById" resultType="com.cjp.pojo.User" parameterType="int">
        select * from mybatis.user where id = #{id}
    </select>
    
    <insert id="insertUser" parameterType="com.cjp.pojo.User" >
      insert into mybatis.user (id,name,pwd)value (#{id},#{name},#{pwd})
    </insert>

    <update id="updateUser" parameterType="com.cjp.pojo.User">
        update mybatis.user set name=#{name},pwd=#{pwd}  where id=#{id} ;
    </update>

    <delete id="deleteUser" parameterType="int" >
        delete from mybatis.user where id=#{id};
    </delete>
</mapper>

测试代码:

package com.cjp.dao;

import com.cjp.pojo.User;
import com.cjp.utils.MybatisUtil;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class UserDaoTest {
    @Test
    public void test() {
        //第一步,获得SqlSession对象
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        try {
            //第二步,执行sql
            //方式一:
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            List<User> userList = mapper.getUserList();
            for (User user : userList) {
                System.out.println(user);
            }
            /*//方式二:(不推荐使用)
        List<User> users = sqlSession.selectList("com.cjp.dao.UserDao.getUserList");
        for (User user : users) {
            System.out.println(user);
        }*/
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            //关闭SqlSession
            sqlSession.close();
        }
    }

    @Test
    public void getUserByIdTest(){
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User user = mapper.getUserById(1004);
        System.out.println(user);
        sqlSession.close();
    }

    @Test
//    增删改查需要提交事务
    public void insertTest(){
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User user = new User(1004, "王五", "1234567");
        int i = mapper.insertUser(user);
        if (i>=1){
            System.out.println("插入成功!");
        }else {
            System.out.println("插入失败!");
        }
        //提交事务
        sqlSession.commit();
        sqlSession.close();
    }

    @Test
    public void updateUserTest(){
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        int i = mapper.updateUser(new User(1004, "元歌", "1433223"));
        if (i>0){
            System.out.println("修改成功!");
        }else {
            System.out.println("修改失败!");
        }
        sqlSession.commit();
        sqlSession.close();
    }

    @Test
    public void deleteUser(){
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        int i = mapper.deleteUser(1003);
        if (i>0){
            System.out.println("删除成功!");
        }else {
            System.out.println("删除失败!");
        }
        sqlSession.commit();
        sqlSession.close();
    }
}
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