MyBatis3系列__01HelloWorld

# MyBatis作为一个ORM框架，其重要程度不用过多介绍。
下面开始一起学习吧：
本博客的编程方法与MyBatis官方文档基本一致：
## 1.创建一个数据库mybatis_learn以及对应的表tbl_employee：
`CREATE DATABASE mybatis_learn;`
```
CREATE TABLE `tbl_employee` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`last_name` varchar(255) DEFAULT NULL,
`gender` char(1) DEFAULT NULL,
`email` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;
```
## 2.创建一个JavaBean(使用了lombok)：
```
package com.mybatis.learn.bean;
import lombok.*;
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class Employee {
private Integer id;
private String lastName;
private String gender;
private String email;
}
```
## 3.正式开始玩Mybatis：
### 3.1 引入依赖或者jar包
```
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>x.x.x</version>
</dependency>
```
### 3.2创建SqlSessionFactory（不/使用xml方式）
使用xml方式：
```
String resource = "mybatis-config.xml";
InputStream inputStream = null;
try {
inputStream = Resources.getResourceAsStream(resource);
} catch (IOException e) {
e.printStackTrace();
}
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
```
使用这种方式时，需要你写一个配置文件mybatis-config.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>
<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://192.168.1.61:3306/mybatis_learn" />
<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="EmployeeMapper.xml" />
</mappers>
</configuration>
```

当然， 你也可以告别繁琐的xml文件配置：
```
DataSource dataSource = BlogDataSourceFactory.getBlogDataSource();
TransactionFactory transactionFactory = new JdbcTransactionFactory();
Environment environment = new Environment("development", transactionFactory, dataSource);
Configuration configuration = new Configuration(environment);
configuration.addMapper(BlogMapper.class);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);
```

###3.3从 SqlSessionFactory 中获取 SqlSession
```
SqlSession session = sqlSessionFactory.openSession();
try {
Employee employee = (Employee) session.selectOne("org.mybatis.example.BlogMapper.selectEmployee", 1);
System.out.println(employee);
} finally {
session.close();
}
```
同时别忘了写具体的sql映射文件：
```
<?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="org.mybatis.example.BlogMapper">
<select id="selectEmployee" resultType="com.mybatis.learn.bean.Employee">
select * from tbl_employee where id = #{id}
</select>
</mapper>
```
这样子就可以正常查询了(lastName 需要在配置文件中使用别名)