二、MyBatis-HelloWorld

create table tbl_employee (
    id int(11) primary key AUTO_INCREMENT comment "ID",
    last_name varchar(20) default null comment "姓名",
    email varchar(20) default null comment "邮件",
    gender varchar(1) default null comment "性别"
)

<!-- 1.mybatis必须依赖包 -->
<dependency>
  <groupId>org.mybatis</groupId>
  <artifactId>mybatis</artifactId>
  <version>3.4.1</version>
</dependency>
<!-- 2.mysql数据库连接驱动 -->
<dependency>
  <groupId>mysql</groupId>
  <artifactId>mysql-connector-java</artifactId>
  <version>5.1.26</version>
</dependency>
<!-- 3.日志-->
<dependency>
  <groupId>log4j</groupId>
  <artifactId>log4j</artifactId>
  <version>1.2.17</version>
</dependency>

package com.atguigu.mybatis.bean;

public class Employee {
    private Integer id;
    private String lastName;
    private String email;
    private String gender;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    @Override
    public String toString() {
        return "Employee [id=" + id + ", lastName=" + lastName + ", email="
                + email + ", gender=" + gender + "]";
    }

}

package com.atguigu.mybatis.dao;
import com.atguigu.mybatis.bean.Employee;

/**
 * mybatis接口式編程
 * @author kancy
 */
public interface EmployeeMapper {
    public Employee getEmpById(Integer id);
}

<?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>
    <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" />
                <property name="username" value="root" />
                <property name="password" value="123456" />
            </dataSource>
        </environment>
    </environments>
    <!-- 将我们写好的sql映射文件（EmployeeMapper.xml）一定要注册到全局配置文件（mybatis-config.xml）中 -->
    <mappers>
        <mapper resource="mappers/EmployeeMapper.xml" />
    </mappers>
</configuration>

<?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.atguigu.mybatis.dao.EmployeeMapper">
<!-- 
namespace:名称空间;指定为接口的全类名
id：唯一标识
resultType：返回值类型
#{id}：从传递过来的参数中取出id值
 -->
    <select id="getEmpById" resultType="com.atguigu.mybatis.bean.Employee">
        select id,last_name lastName,email,gender from tbl_employee where id = #{id}
    </select>
</mapper>

<?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>

public SqlSessionFactory getSqlSessionFactory() throws IOException {
    String resource = "mybatis-config.xml";
    InputStream inputStream = Resources.getResourceAsStream(resource);
    return new SqlSessionFactoryBuilder().build(inputStream);
}

/**
 * 1、根据xml配置文件（全局配置文件）创建一个SqlSessionFactory对象 有数据源一些运行环境信息
 * 2、sql映射文件；配置了每一个sql，以及sql的封装规则等。 
 * 3、将sql映射文件注册在全局配置文件中
 * 4、写代码：
 *         1）、根据全局配置文件得到SqlSessionFactory；
 *         2）、使用sqlSession工厂，获取到sqlSession对象使用他来执行增删改查
 *             一个sqlSession就是代表和数据库的一次会话，用完关闭
 *         3）、使用sql的唯一标志来告诉MyBatis执行哪个sql。sql都是保存在sql映射文件中的。
 * @throws IOException
 */
@Test
public void test01() throws IOException {
    // 2、获取sqlSession实例，能直接执行已经映射的sql语句
    // sql的唯一标识：statement Unique identifier matching the statement to use.
    // 执行sql要用的参数：parameter A parameter object to pass to the statement.
    SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
    SqlSession openSession = sqlSessionFactory.openSession();
    try {
        Employee employee = openSession.selectOne(
                "com.atguigu.mybatis.dao.EmployeeMapper.getEmpById", 1);
        System.out.println(employee);
    } finally {
        openSession.close();
    }
}

public SqlSessionFactory getSqlSessionFactory() throws IOException {
    String resource = "mybatis-config.xml";
    InputStream inputStream = Resources.getResourceAsStream(resource);
    return new SqlSessionFactoryBuilder().build(inputStream);
}

@Test
public void test02() throws IOException {
    // 1、获取sqlSessionFactory对象
    SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
    // 2、获取sqlSession对象
    SqlSession openSession = sqlSessionFactory.openSession();
    try {
        // 3、获取接口的实现类对象
        //会为接口自动的创建一个代理对象，代理对象去执行增删改查方法
        EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
        Employee employee = mapper.getEmpById(1);
        System.out.println(mapper.getClass());
        System.out.println(employee);
    } finally {
        openSession.close();
    }
}