Java学习-MyBatis学习(一)

MyBatis

MyBatis历史

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，并且改名为MyBatis。2013年11月迁移到Github。
iBATIS一词来源于“internet”和“abatis”的组合，是一个基于Java的持久层框架。iBATIS提供的持久层框架包括SQL Maps和Data Access Objects（DAOs）

MyBatis特性

支持定制化SQL，存储过程及高级映射的优秀持久层框架
避免了几乎所有的JDBC代码和手动设置参数以及获取结果集
使用简单的XML和注解用于配置和原始映射，将接口和Java的POJO映射到数据库中记录
是一个半自动化的ORM(Object Relation Mapping)框架

MyBatis-Maven配置

<dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.7</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.23</version>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
    </dependencies>

在这里插入图片描述

MyBatis的核心配置文件

建议名称mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <!-- 配置连接数据库环境 -->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>        <!-- 使用原始JDBC的方式管理事务，代码提交时需要手动提交-->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://192.168.29.201:3306/mybatis"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <!-- 引入映射文件 -->
    <mappers>
        <mapper resource="mappers/UserMapper.xml"/>
    </mappers>
</configuration>

<!-- log4j.xml配置文件-- >
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
    <appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">
        <param name="Encoding" value="UTF-8"/>
        <layout class="org.apache.log4j.PatternLayout">
            <param name="ConversionPattern" value="%-5p %d{MM-dd HH:mm:ss,SSS}
%m (%F:%L) \n"/>
        </layout>
    </appender>
    <logger name="java.sql">
        <level value="debug"/>
    </logger>
    <logger name="org.apache.ibatis">
        <level value="info"/>
    </logger>
    <root>
        <level value="debug"/>
        <appender-ref ref="STDOUT"/>
    </root>
</log4j:configuration>

创建mapper接口

# 创建数据库和表
mysql> create database mybatis;
Query OK, 1 row affected (0.00 sec)
mysql> use mybatis;
Database changed
mysql> create table t_user(id int primary key auto_increment,username varchar(20),password varchar(20),age int,sex char,email varchar(20));
Query OK, 0 rows affected (0.01 sec)

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.lotus.mybatis.mapper.UserMapper">
	<!--int insertUser();-->
    <insert id="insertUser">
        insert into t_user values(null,'edison','123456',23,'男','edison@qq.com')
    </insert>
    <!--int updateUser();-->
    <update id="updateUser">
        update t_user set username = 'dizzy' where id = 3
    </update>
    <!--int deleteUser();-->
    <delete id="deleteUser">
        delete from t_user where id = 3
    </delete>
    <!-- getUserById -->
    <!--
    查询功能标签必须设置resultType或resultMap
    resultType：设置默认的映射关系
    resultMap：设置自定义的映射关系
    -->
    <select id="getUserById" resultType="com.lotus.mybatis.pojo.User">
        select * from t_user where id = 4
    </select>
    <!-- List<User> getAllUser(); -->
    <select id="getAllUser" resultType="com.lotus.mybatis.pojo.User">
        select * from t_user
    </select>
</mapper>

package com.lotus.mybatis.mapper;

/**
 * MyBatis面向接口编程的两个一致
 * ①映射文件的namespace要和Mapper接口全类名一致
 * ②映射文件中SQL语句的id要和mapper中的方法名一致
 */
public interface UserMapper {
     /**
     * 添加用户信息
     */
    int insertUser();
    /**
     * 删除用户
     */
    int deleteUser();
    /**
     * 修改用户
     */
    int updateUser();

    /**
     * 查询数据
     */
    User getUserById();
    /**
     * 查询所有用户信息
     */
    List<User> getAllUser();
}
package com.lotus.mybatis.pojo;
public class User {
    private Integer id;
    private String username;
    private String password;
    private Integer age;
    private String sex;
    private String email;
    public User() {
    }
    public User(Integer id, String username, String password, Integer age, String sex, String email) {
        this.id = id;
        this.username = username;
        this.password = password;
        this.age = age;
        this.sex = sex;
        this.email = email;
    }
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
    public String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }
    public String getEmail() {
        return email;
    }
    public void setEmail(String email) {
        this.email = email;
    }
    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                ", age=" + age +
                ", sex='" + sex + '\'' +
                ", email='" + email + '\'' +
                '}';
    }
}

创建MyBatis映射文件

ORM对象映射关系
- 对象：Java实体类对象
- 关系：关系型数据库
- 映射：二者之间的对应关系
映射文件命名规则
- 表所对应的实体类名+Mapper.xml-----如表t_user,映射的实体类为User,
MyBatis可以面向接口操作数据，要保证两个一致
SqlSession：代表Java程序和数据库之前的会话
SqlSessionFactory：生产SqlSession的工厂
工厂模式：创建某一个对象，使用的过程基本固定，那么我们就可以创建这个对象的相关代码封装到一个“工厂类”中，以后使用这个工厂类生产我们需要的对象

//SqlSession默认不自动提交事务，需要自动提交事务,使用openSession(true)自动提交事务

public class MyBatisTest {
   @Test
    public void testMyBatis() throws IOException {
        //加载核心配置文件
        InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
        //获取SqlSessionFactoryBuilder
        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
        //SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(is);
        //获取SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //获取Mapper接口对象
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        //测试功能
        int res = mapper.insertUser();
        //提交事务
        sqlSession.commit();
        System.out.println(res);
    }
    @Test
    public void testCRUD() throws IOException {
        //加载核心配置文件
        InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
        //获取SqlSessionFactoryBuilder
        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
        //SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(is);
        //获取SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession(true);
        //获取Mapper接口对象
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        //int res = mapper.updateUser();
        //int res = mapper.deleteUser();
        /*User user = mapper.getUserById();
        System.out.println(user);*/
        //System.out.println(res);
        List<User> users = mapper.getAllUser();
        users.forEach(user-> System.out.println(user));
    }
}