helloworld（入门）
建表语句
CREATE TABLE `tbl_employee` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`last_name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
`gender` char(1) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
`email` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 2 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci ROW_FORMAT = Dynamic;
INSERT INTO `tbl_employee` VALUES (1, 'tom', '0', 'tom@qq.com');
实体类：
@Data
@ToString
public class Employee {
private Integer id;
private String lastName;
private String email;
private String gender;
}
pom.xml
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.4.1</version>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.18.16</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.47</version>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.13</version>
</dependency>
log4j.xml放在类路径下：
<?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)
" />
</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>
sql映射文件EmployeeMapper.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.wj.EmployeeMapper">
<!--
namespace:命名空间
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="selectEmp" resultType="com.wj.bean.Employee">
select
id
,last_name as lastName
,email
,gender
from
tbl_employee
where id = #{id}
</select>
</mapper>
全局配置文件：
<?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="1234"/>
</dataSource>
</environment>
</environments>
<!--将我们写好的sql映射文件一定要注册在全局配置文件中-->
<mappers>
<mapper resource="EmployeeMapper.xml"/>
</mappers>
</configuration>
编写测试类：
@Test
public void test() throws IOException {
//1.根据xml配置文件（全局配置文件）创建一个SqlSessionFactory对象
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
//2.获取sqlSession实例，直接执行已经映射的sql语句
SqlSession session = sqlSessionFactory.openSession();
try {
// sql的唯一标识 (namespace + id) 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.
Employee employee = session.selectOne("com.wj.EmployeeMapper.selectEmp", 1);
System.out.println(employee);
} finally {
session.close();
}
}
执行结果：
总结：
-
根据xml配置文件（全局配置文件）创建一个SqlSessionFactory对象（包含数据源相关信息）
-
编写sql映射文件，配置了每一个sql和sql的封装规则等
-
将SQL的映射文件注册在全局配置文件中
-
写代码
-
根据全局配置文件获取SqlSessionFactory
-
使用SqlSession工厂，获取sqlSession（一个sqlSession就是和数据库的一次会话，用完关闭）
-
使用sql的唯一标识告诉Mybatis执行哪个sql。sql都是保存在Sql映射文件中的。
-
项目结构：
面向接口编程
官方文档中：
大意是说上一种方法是旧版本的写法，新版本中，可以使用接口的方式，使代码更加简介，可以避免类型转换等出错。
创建一个接口:EmployeeMapper.java
public interface EmployeeMapper {
public Employee getEmpById(Integer id);
}
修改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="com.wj.dao.EmployeeMapper">
<!--
namespace:命名空间 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.wj.bean.Employee">
select
id
,last_name as lastName
,email
,gender
from
tbl_employee
where id = #{id}
</select>
</mapper>
测试：
@Test
public void test01() throws IOException {
//1.根据xml配置文件（全局配置文件）创建一个SqlSessionFactory对象
SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
SqlSession session = sqlSessionFactory.openSession();
try {
EmployeeMapper employeeMapper= session.getMapper(EmployeeMapper.class);
Employee emp = employeeMapper.getEmpById(1);
System.out.println(emp);
} finally {
session.close();
}
}
private SqlSessionFactory getSqlSessionFactory() throws IOException {
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
return new SqlSessionFactoryBuilder().build(inputStream);
}
执行结果：
此时，我们发现，并没有为EmployeeMapper编写实现类，竟然也执行了方法，打断点，发现用的是代理类实现
