MyBatis学习（一）

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。

首先按照以往使用JDBC的方式来访问数据库：

JDBC实现数据库操作

   public static void main(String[] args) {
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;

        try {
            //1.加载数据库驱动
            Class.forName("com.mysql.jdbc.Driver");
            //2.获取数据库连接
            DriverManager.getConnection("jdbc:mysql://localhost:3306/mybatis?characterEncoding=utf-8",
                    "root", "root");
            //3.定义sql语句
            String sql = "select * from user where username = ?";
            //4.获取预处理对象
            preparedStatement = connection.prepareStatement(sql);
            //5.设置参数
            preparedStatement.setString(1, "王五");
            //6.查询数据库
            resultSet = preparedStatement.executeQuery();
            //7.遍历查询的结果集
            while (resultSet.next()) {
                System.out.println(resultSet.getString("id") + "--" +
                        resultSet.getString("username"));
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            //8.释放资源
            if (resultSet != null) {
                try {
                    resultSet.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if (preparedStatement != null) {
                try {
                    preparedStatement.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if (connection != null) {
                try {
                    connection.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
    }

虽然上述未经封装的JDBC代码可实现查询数据库记录的操作，但是分析上述代码可发现以下问题：

针对上述存在的问题，可采用下述办法进行解决：

而本次学习的MyBatis即可实现上述操作。

pom.xml

    <dependencies>
        <dependency>
            <groupid>org.mybatis</groupid>
            <artifactid>mybatis</artifactid>
            <version>3.4.5</version>
        </dependency>
        <dependency>
            <groupid>junit</groupid>
            <artifactid>junit</artifactid>
            <version>4.10</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupid>mysql</groupid>
            <artifactid>mysql-connector-java</artifactid>
            <version>5.1.6</version>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupid>log4j</groupid>
            <artifactid>log4j</artifactid>
            <version>1.2.12</version>
        </dependency>
    </dependencies>

User.java

public class User implements Serializable {
    private Integer id;
    private String username;
    private Date birthday;
    private String sex;
    private String address;

    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 Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "User [id=" + id + ", username=" + username + ", birthday=" + birthday + ", " +
                "sex=" + sex + ", address=" + address + "]";
    }
}

UserDao.java

public interface UserDao {
    List<user> findAll();
}
</user>

UserDao.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" >
<mapper namespace="com.dcyl.dao.UserDao">
    <select id="findAll" resulttype="com.dcyl.domain.User">
        select * from user
    </select>
</mapper>

SqlMapConfig.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">
<configuration>
    <!-- 配置mybatis的环境 -->
    <environments default="mysql">
        <!-- 配置mysql的环境 -->
        <environment id="mysql">
            <!-- 配置事务的类型 -->
            <transactionmanager type="JDBC"></transactionmanager>
            <!-- 配置连接数据库的信息：用的是数据源(连接池) -->
            <datasource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver">
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis">
                <property name="username" value="root">
                <property name="password" value="root">
            </property></property></property></property></datasource>
        </environment>
    </environments>
    <!-- 告知mybatis映射配置的位置 -->
    <mappers>
        <mapper resource="com/dcyl/dao/UserDao.xml">
    </mapper></mappers>
</configuration>

MyBatisTest.java

public class MybatisTest {
    public static void main(String[] args) throws Exception {
        //1.读取配置文件
        InputStream in = Resources.getResourceAsStream("SqlMapConfig.xml");
        //2.创建SqlSessionFactory的构建者对象
        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
        //3.使用构建者创建工厂对象SqlSessionFactory
        SqlSessionFactory factory = builder.build(in);
        //4.使用SqlSessionFactory生产SqlSession对象
        SqlSession session = factory.openSession();
        //5.使用SqlSession创建dao接口的代理对象
        UserDao userDao = session.getMapper(UserDao.class);
        //6.使用代理对象执行查询所有方法
        List<user> users = userDao.findAll();
        for (User user : users) {
            System.out.println(user);
        }
        //7.&#x91CA;&#x653E;&#x8D44;&#x6E90;
        session.close();
        in.close();
    }
}
</user>

至此关于MyBatis的入门案例已经完成，接下来就是关于MyBatis的具体细节的讲解。

Original: https://www.cnblogs.com/dcyL/p/16410569.html
Author: dcyL
Title: MyBatis学习（一）