Mybatis框架(一)mybatis入门
mybatis的使用
mybatis中文文档：https://mybatis.org/mybatis-3/zh/index.html
如果使用 Maven 来构建项目，则需将下面的依赖代码置于 pom.xml 文件中：
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>x.x.x</version>
</dependency>
一、数据库环境：
CREATE DATABASE `mybatis`;
USE `mybatis`;
CREATE TABLE `user`(
`id` INT(20) NOT NULL PRIMARY KEY,
`name` VARCHAR(30) DEFAULT NULL,
`pwd` VARCHAR(30) DEFAULT NULL
)ENGINE=INNODB DEFAULT CHARSET=utf8;
INSERT INTO `user`(`id`,`name`,`pwd`) VALUES
(1,'张三','123456'),
(2,'张三','123456'),
(3,'李四','123890')//加群1025684353一起吹水聊天
二、创建maven项目导入依赖
2.1 IDEA连接数据库：
2.2 导入项目依赖:
maven仓库地址：****https://mvnrepository.com/
<!--导入依赖-->
<dependencies>
<!--mysql驱动-->
<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>3.5.2</version>
</dependency>
<!--junit-->
<dependency>
<groupId>junit</groupId>//加群1025684353一起吹水聊天
<artifactId>junit</artifactId>
<version>4.12</version>
</dependency>
</dependencies>
三、创建mybatis核心配置文件：
在src/main/resources下创建：mybatis-config.xml核心配置文件
官方伪代码：
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<?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}"/>//加群1025684353一起吹水聊天
<property name="username" value="${username}"/>
<property name="password" value="${password}"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="org/mybatis/example/BlogMapper.xml"/>
</mappers>
</configuration>
配置文件代码:
<?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">//加群1025684353一起吹水聊天
<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="123456"/>
</dataSource>
</environment>
</environments>
</configuration>
四、编写mybatis工具类
package com.kuang.utils;
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;
//sqlSessionFactory --> sqlSession
public class MybatisUtils {
private static SqlSessionFactory sqlSessionFactory;
static{
try {//加群1025684353一起吹水聊天
//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，我们就可以从中获得 SqlSession 的实例了。
// SqlSession 完全包含了面向数据库执行 SQL 命令所需的所有方法。
public static SqlSession getSqlSession(){
return sqlSessionFactory.openSession();
}
}
五、编写实体类
字段与字段类型要与数据库一一对应
package com.study.pojo;
//实体类
public class User {
private int id;
private String name;//加群1025684353一起吹水聊天
private String pwd;
public User() {
}
public User(int id, String name, String pwd) {
this.id = id;
this.name = name;
this.pwd = pwd;
}
public int getId() {
return id;
}
public void setId(int 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 + '\'' +
'}';
}
}
六、编写dao接口
package com.study.dao;
public interface UserMapper {
List<User> getUserList();
}
七、在UserMapper接口类同包下编写Mapper文件实现接口
<?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">
<!--namespace=绑定一个对应的Dao/Mapper接口-->
<mapper namespace="com.study.dao.UserMapper">//加群1025684353一起吹水聊天
<!--select查询语句-->
<!--id="方法名" resultType="类型"-->
<select id="getUserList" resultType="com.study.pojo.User">
select * from mybatis.user
</select>
</mapper>
八、编写完毕,需要在mybatis-config.xml中注册Mapper.xml
<mappers>
<mapper resource="com/study/dao/UserMapper.xml"/>
</mappers>
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如：
注意：检查文件目录结构是否正确
九、测试
在test/java/com/study/dao下创建UserMapperTest.java测试类
如图：
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编写测试代码:
public class UserMapperTest {
@Test
public void test(){
//第一步：获得SqlSession对象
SqlSession sqlSession = MybatisUtils.getSqlSession();
//方式一：getMapper
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
List<User> userList = userMapper.getUserList();
for (User user : userList) {
System.out.println(user);
}
//关闭SqlSession
sqlSession.close();//加群1025684353一起吹水聊天
}
运行结果
你们可以能会遇到的问题：
- 配置文件没有注册
- 绑定接口错误。
- 方法名不对
- 返回类型不对
- Maven导出资源问题 #### 特别注意：mybatis配置文件中不能出现中文注释！
资源导出问题解决：在pom.xml中添加
建议每次创建项目都提前添加资源过滤配置
<!--在build中配置resources，来防止我们资源导出失败的问题-->
<build>
<resources>
<resource>
<directory>src/main/resources</directory>
<includes>
<include>**/*.properties</include>
<include>**/*.xml</include>
</includes>
<filtering>true</filtering>//加群1025684353一起吹水聊天
</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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如图：
最后，祝大家早日学有所成，拿到满意offer，快速升职加薪，走上人生巅峰。 可以的话请给我一个三连支持一下我哟，我们下期再见
