<span>第一个Mybatis程序</span>
第一个Mybatis程序（狂神）
思路：搭建环境–>导入Mybatis–>编写代码–>测试
2.1 搭建环境
1、搭建数据库
CREATE DATABASE mybatis;
CREATE TABLE USER(
id INT(20) NOT NULL PRIMARY KEY,
NAME VARCHAR(20) DEFAULT NULL,
pwd VARCHAR(20) DEFAULT NULL
)ENGINE=INNODB DEFAULT CHARSET=utf8;
INSERT INTO USER (id,NAME,pwd)VALUES
(1,'张三','123456'),
(2,'李四','123456'),
(3,'王五','123456')
SELECT * FROM USER
2、新建项目
01.新建一个普通的Maven项目
02.删除src目录
03.导入依赖数据库，mybatis junit
<!--import dependencies-->
<dependencies>
<!--mysql driver-->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.47</version>
</dependency>
<!--mybatis-->
<!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.6</version>
</dependency>
<!--junit-->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
</dependency>
</dependencies>
<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>
2.2 创建一个模块
- 编写mybatis的核心配置文件mybatis-config.xml
- 资源过滤改为useSSL=false
- resource绑定mapper，需要使用路径！
<?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 core file-->
<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?useSSL=false&useUnicode=true&characterEncoding=UTF-8"/>
<property name="username" value="root"/>
<property name="password" value="12345"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="com/kuang/dao/UserMapper.xml"/>
</mappers>
</configuration>
编写mybatis工具类
public class MybatisUtils {
//SqlSessionFactory -->SqlSession
private static SqlSessionFactory sqlSessionFactory;
static {
try {
//使用Mybaties第一步：获取sqlSessionFactory对象
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
} catch (Exception 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(){
// SqlSession sqlSession = sqlSessionFactory.openSession();
// return sqlSession;
return sqlSessionFactory.openSession();
}
}
2.3 编写代码
实体类
//实体类
public class User {
private int id;
private String name;
private String pwd;
public User() {
}
public User(int id, String name, String pwd) {
this.id = id;
this.name = name;
this.pwd = pwd;
}
//set.get
@Override
public String toString() {
return "User{" +
"id=" + id +
", name='" + name + '\'' +
", pwd='" + pwd + '\'' +
'}';
}
}
Dao接口
public interface UserDao {
List<User> getUserList();
}
- 接口实现类由原来的UserDaoImpl转变成一个Mapper配置文件。
- namespace绑定一个对应的Dao/Mapper接口
<?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="yu.dao.UserDao">
<!--sql-->
<select id="getUserList" resultType="yu.pojo.User">
select * from mybatis.user
</select>
</mapper>
junit测试
注意点：
- org.apache.ibatis.binding.BindingException: Type interface com.kuang.dao.UserDao is not known to the MapperRegistry.
- 每一个Mapper.xml都需要在Mybatis核心配置文件中注册。配置文件可能会失效，在build中配置resoureces，来防止我们资源导出失效的问题
- getMapper用法：指明一个Dao接口的class，调用他的方法，即可从数据库中返回
SqlSession用途
① 获取对应的Mapper，让映射器通过命名空间和方法名称找到对应的SQL，发送给数据库执行后返回结果。
② 直接使用SqlSession，通过命名信息去执行SQL返回结果，该方式是IBatis版本留下的，SqlSession通过Update、Select、Insert、Delete等方法操作。
@Test
public void test(){
//第一步：获得SqlSession对象
SqlSession sqlSession = MybatisUtils.getSqlSession();
//方式一：getMapper
UserDao userDao = sqlSession.getMapper(UserDao.class);
List<User> userList = userDao.getUserList();
for (User user : userList) {
System.out.println(user);
}
//关闭SqlSession
sqlSession.close();
}
<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>
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