Mybatis学习之路01环境搭建及第一个测试程序
From 狂神说https://www.bilibili.com/video/BV1NE411Q7Nx
1、创建普通Maven项目,可以删去src目录创建maven父子项目,重复利用依赖,提高练习效率(子项目可以使用父项目的依赖)
2、导入需要的依赖
<dependencies>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.25</version>
</dependency>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.7</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<scope>test</scope>
</dependency>
</dependencies>
3、编写mybatis核心配置文件(查看官方中文文档)
<?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="${driver}"/>
<property name="url" value="${url}"/>
<property name="username" value="${username}"/>
<property name="password" value="${password}"/>
</dataSource>
</environment>
</environments>
<!-- 注意点:每一个Mapper.xml都需要在Mybatis核心配置文件中注册-->
<mappers>
<mapper resource="org/mybatis/example/BlogMapper.xml"/>
</mappers>
</configuration>
4、编写mybatis工具类(减少反复调用factory类次数)
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.IOException;
import java.io.InputStream;
public class MybatisUtil {
private static SqlSessionFactory sqlSessionFactory;
static{
try {
//使用Mybatis第一步:获取sqlSessionFactory对象
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
} catch (IOException e) {
e.printStackTrace();
}
}
//既然有了 SqlSessionFactory,顾名思义,我们可以从中获得 SqlSession 的实例。SqlSession 提供了在数据库执行 SQL 命令所需的所有方法。你可以通过 SqlSession 实例来直接执行已映射的 SQL 语句。
public static SqlSession getSqlSession(){
return sqlSessionFactory.openSession();
}
}
5、编写代码
- 实体类
public class User {
private Integer id;
private String name;
private String pwd;
public User() {
}
public User(Integer id, String name, String pwd) {
this.id = id;
this.name = name;
this.pwd = pwd;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPwd() {
return pwd;
}
public void setPwd(String pwd) {
this.pwd = pwd;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", name='" + name + '\'' +
", pwd='" + pwd + '\'' +
'}';
}
}
- Dao接口
import com.smxy.entity.User;
import java.util.List;
interface UserDao {
List<User> getUserList();
}
- 接口实现类,由原来的UserImpl转换为一个Mapper配置文件(.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.smxy.dao.UserDao">
<!-- select查询语句-->
<select id="getUserList" resultType="com.smxy.entity.User">
select * from mybatis.user;
</select>
</mapper>
6、测试
public class UserMapperTest {
@Test
public void test(){
SqlSession sqlSession = MybatisUtil.getSqlSession();
//方式一:getMapper
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
List<User> userList = userMapper.getUserList();
//面向接口编程
for (User user : userList) {
System.out.println(user);
}
//关闭sqlSession
sqlSession.close();
}
}
7、Maven资源导出问题
.xml文件未放置在resources文件夹内时就会遇到
maven由于他的约定大于配置,我们之后可以遇到我们写的配置文件,无法被导出或者生效的问题,解决方案:(在pom.xml内添加如下代码)
<build>
<resources>
<resource>
<directory>src/main/resources</directory>
<includes>
<include>**/*.properties</include>
<include>**/*.xml</include>
</includes>
<filtering>true</filtering>
</resource>
<resource>
<directory>src/main/java</directory>
<includes>
<include>**/*.properties</include>
<include>**/*.xml</include>
</includes>
<filtering>true</filtering>
</resource>
</resources>
</build>