The mybatis learning summary series comes from Lonely Wolf Blog: https://www.cnblogs.com/xdp-gacl/p/4261895.html
1. Introduction to Mybatis
MyBatis is an excellent persistence layer framework that supports plain SQL queries , stored procedures and advanced mappings . MyBatis eliminates almost all JDBC code and manual setting of parameters and retrieval encapsulation of result sets. MyBatis can use simple XML or annotations for configuration and primitive mapping to map interfaces and Java POJOs (Plain Old Java Objects, ordinary Java objects) to records in the database.
Second, mybatis quick start
2.1. Prepare the development environment
1. Create a test project, either a normal java project or a JavaWeb project
2. Add the corresponding jar package
【mybatis】
mybatis-3.1.1.jar
[MYSQL driver package]
mysql-connector-java-5.1.7-bin.jar
3. Create databases and tables for MySQL databases
The SQL script is as follows:
1 create database mybatis;
2 use mybatis;
3 CREATE TABLE users(id INT PRIMARY KEY AUTO_INCREMENT, NAME VARCHAR(20), age INT);
4 INSERT INTO users(NAME, age) VALUES('孤傲苍狼', 27);
5 INSERT INTO users(NAME, age) VALUES('White Tiger God Emperor', 27 );
Execute the SQL script in the MySQL database to complete the operation of creating the database and table
At this point, the preparatory work for the development environment has been completed.
2.2. Use MyBatis to query the data in the table
1. Add the configuration file conf.xml of Mybatis
Create a conf.xml file in the src directory
The content in the conf.xml file is as follows:
1 <?xml version="1.0" encoding="UTF-8"?> 2 <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> 3 <configuration> 4 <environments default="development"> 5 <environment id="development"> 6 <transactionManager type="JDBC" /> 7 <!-- Configure database connection information--> 8 <dataSource type="POOLED"> 9 <property name="driver" value="com.mysql.jdbc.Driver" /> 10 <property name="url" value="jdbc:mysql://localhost:3306/mybatis" /> 11 <property name="username" value="root" /> 12 <property name="password" value="XDP" /> 13 </dataSource> 14 </environment> 15 </environments> 16 17 </configuration>
2、定义表所对应的实体类，
User类的代码如下：
1 package me.gacl.domain;
2
3 /**
4 * @author gacl
5 * users表所对应的实体类
6 */
7 public class User {
8
9 //实体类的属性和表的字段名称一一对应
10 private int id;
11 private String name;
12 private int age;
13
14 public int getId() {
15 return id;
16 }
17
18 public void setId(int id) {
19 this.id = id;
20 }
21
22 public String getName() {
23 return name;
24 }
25
26 public void setName(String name) {
27 this.name = name;
28 }
29
30 public int getAge() {
31 return age;
32 }
33
34 public void setAge(int age) {
35 this.age = age;
36 }
37
38 @Override
39 public String toString() {
40 return "User [id=" + id + ", name=" + name + ", age=" + age + "]";
41 }
42 }
3、定义操作users表的sql映射文件userMapper.xml
创建一个me.gacl.mapping包，专门用于存放sql映射文件，在包中创建一个userMapper.xml文件
userMapper.xml文件的内容如下：
1 <?xml version="1.0" encoding="UTF-8" ?>
2 <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
3 <!-- 为这个mapper指定一个唯一的namespace，namespace的值习惯上设置成包名+sql映射文件名，这样就能够保证namespace的值是唯一的
4 例如namespace="me.gacl.mapping.userMapper"就是me.gacl.mapping(包名)+userMapper(userMapper.xml文件去除后缀)
5 -->
6 <mapper namespace="me.gacl.mapping.userMapper">
7 <!-- 在select标签中编写查询的SQL语句， 设置select标签的id属性为getUser，id属性值必须是唯一的，不能够重复
8 使用parameterType属性指明查询时使用的参数类型，resultType属性指明查询返回的结果集类型
9 resultType="me.gacl.domain.User"就表示将查询结果封装成一个User类的对象返回
10 User类就是users表所对应的实体类
11 -->
12 <!--
13 根据id查询得到一个user对象
14 -->
15 <select id="getUser" parameterType="int"
16 resultType="me.gacl.domain.User">
17 select * from users where id=#{id}
18 </select>
19 </mapper>
4、在conf.xml文件中注册userMapper.xml文件
1 <?xml version="1.0" encoding="UTF-8"?> 2 <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> 3 <configuration> 4 <environments default="development"> 5 <environment id="development"> 6 <transactionManager type="JDBC" /> 7 <!-- 配置数据库连接信息 --> 8 <dataSource type="POOLED"> 9 <property name="driver" value="com.mysql.jdbc.Driver" /> 10 <property name="url" value="jdbc:mysql://localhost:3306/mybatis" /> 11 <property name="username" value="root" /> 12 <property name="password" value="XDP" /> 13 </dataSource> 14 </environment> 15 </environments> 16 17 <mappers> 18 <!-- 注册userMapper.xml文件， 19 userMapper.xml位于me.gacl.mapping这个包下，所以resource写成me/gacl/mapping/userMapper.xml--> 20 <mapper resource="me/gacl/mapping/userMapper.xml"/> 21 </mappers> 22 23 </configuration>
5、编写测试代码：执行定义的select语句
创建一个Test1类，编写如下的测试代码：
package me.gacl.test;
import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import me.gacl.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;
public class Test1 {
public static void main(String[] args) throws IOException {
//mybatis的配置文件
String resource = "conf.xml";
//使用类加载器加载mybatis的配置文件（它也加载关联的映射文件）
InputStream is = Test1.class.getClassLoader().getResourceAsStream(resource);
//构建sqlSession的工厂
SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is);
//使用MyBatis提供的Resources类加载mybatis的配置文件（它也加载关联的映射文件）
//Reader reader = Resources.getResourceAsReader(resource);
//构建sqlSession的工厂
//SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
//创建能执行映射文件中sql的sqlSession
SqlSession session = sessionFactory.openSession();
/**
* 映射sql的标识字符串，
* me.gacl.mapping.userMapper是userMapper.xml文件中mapper标签的namespace属性的值，
* getUser是select标签的id属性值，通过select标签的id属性值就可以找到要执行的SQL
*/
String statement = "me.gacl.mapping.userMapper.getUser";//映射sql的标识字符串
//执行查询返回一个唯一user对象的sql
User user = session.selectOne(statement, 1);
System.out.println(user);
}
}