MyBatis 速成手册

入门案例

现有一张数据表：

mysql> use mybatis;
Database changed
mysql> select * from tbl_employee;
+----+-----------+--------+-------------+
| id | last_name | gender | email |
+----+-----------+--------+-------------+
|  1 | tom | 0      | tom@163.com |
+----+-----------+--------+-------------+
1 row in set (0.00 sec)

该如何通过MyBatis对其进行查询？首先创建对应的Java类：

package com.wwj.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 + "]";
 }
}

其次编写MyBatis的全局配置文件(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:///mybatis"/>
          <property name="username" value="root"/>
           <property name="password" value="123456"/>
         </dataSource>
     </environment>
 </environments>
 <mappers>
  <mapper resource="EmployeeMapper.xml"/>
 </mappers>
</configuration>

全局配置文件中主要配置的是数据源信息，然后是最后的mappers标签，该标签配置的是sql语句的映射文件。

所以我们接着创建sql语句的映射文件(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.wwj.mybatis.bean.Employee">
  <select id="selectEmp" resultType="com.wwj.mybatis.bean.Employee">
     select id,last_name lastName,email,gender from tbl_employee where id = #{id}
   </select>
</mapper>

其中mapper标签的namespace属性设置的是需要映射的类全名；select标签表示查询语句，其中的id属性是该sql的唯一标识，resultType表示返回值的类型；然后在select标签中编写需要执行的sql语句。

一切准备就绪后，开始编写测试代码：

@Test
void test() throws IOException {
 String resource = "mybatis-config.xml";
 InputStream inputStream = Resources.getResourceAsStream(resource);
 SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
 SqlSession session = sessionFactory.openSession();
 Employee employee = session.selectOne("com.wwj.mybatis.bean.Employee.selectEmp",1);
 System.out.println(employee);
 session.close();
}

https://mp.weixin.qq.com/s/wmkRTbBjWMd-SDaJm6W-FA