快速入门理解Mybatis——自定义框架实现数据库查询操作（一）

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

package domain;
import java.io.Serializable;
import java.util.Date;
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;
    }
}

package dao;
import domain.User;
import java.util.List;
public interface UserDao {
    /**
     * 查询所有用户
     * @return
     */
    List<User> findAll();
}

<?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="dao.UserDao">
    <!-- 配置查询所有操作，查询结果封装在User类里 -->
    <select id="findAll" resultType="domain.User">
        select * from user;
    </select>
</mapper>

<?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">
<!--mybatis的主配置文件-->
<configuration>
    <!--配置环境-->
    <environments default="mysql">
        <!--配置mysql的环境-->
        <environment id="mysql">
            <!--配置事务类型-->
            <transactionManager type="JDBC"></transactionManager>
            <!--配置数据源（连接池）-->
            <dataSource type="POOLED">
                <!--配置连接数据库的4个基本信息-->
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/eesy_mybatis"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
    <!-- 告知mybatis映射配置的位置 -->
    <mappers>
        <mapper resource="dao/UserDao.xml"/>
    </mappers>
</configuration>

package test;
import dao.UserDao;
import domain.User;
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 java.io.IOException;
import java.io.InputStream;
import java.util.List;
public class MybatisTest {
    public static void main(String[] args) throws IOException {
        // 读取配置文件
        InputStream in = Resources.getResourceAsStream("sqlMapConfig.xml");
        // 创建SqlSessionFactory工厂
        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
        SqlSessionFactory factory = builder.build(in);
        // 使用工厂生产SqlSession
        SqlSession session = factory.openSession();
        // 使用SqlSession创建Dao接口的代理对象
        UserDao userDao = session.getMapper(UserDao.class);
        // 使用代理对象执行dao中的方法
        List<User> users = userDao.findAll();
        for (User user : users) {
            System.out.println(user);
        }
        // 释放资源
        session.close();
        in.close();
    }
}

package dao;
import domain.User;
import org.apache.ibatis.annotations.Select;
import java.util.List;
public interface UserDao {
    /**
     * 查询所有用户
     * @return
     */
    @Select("select * from user")
    List<User> findAll();
}

<mappers>
    <mapper class="dao.UserDao"/>
</mappers>

SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build(in);

SqlSession session = factory.openSession();

UserDao userDao = session.getMapper(UserDao.class);