第一个Mybatis程序
流程思路：搭建环境 > 导入依赖 > 编写代码 > 单元测试
1.搭建环境
搭建数据库
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, '凡尘', '123456'),
(2, '张三', '123456'),
(3, '李四', '134343'),
(4, '王五', '1234343'),
(5, '赵六', '044456');
新建项目
-
新建一个普通的maven项目
-
删除src目录
-
导入maven依赖
<dependencies> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>8.0.18</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> </dependency> </dependencies>
2.创建模块
创建Mybatis核心配置文件
<configuration>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.cj.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&useUnicode=true&characterEncoding=UTF-8&serverTimezone=GMT"/>
<property name="username" value="root"/>
<property name="password" value="123456"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="com/haojing/dao/UserMapper.xml" />
</mappers>
</configuration>
编写Mybatis工具类
package com.haojing.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;
public class MybatisUtils {
private static SqlSessionFactory sqlSessionFactory;
static {
try {
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
}catch (IOException e) {
e.printStackTrace();
}
}
public static SqlSession getSqlSession() {
return sqlSessionFactory.openSession();
}
}
3.编写代码
实体类
package com.haojing.pojo;
public class User {
public int id;
public String name;
public 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 + ''' +
'}';
}
}
DAO接口
package com.haojing.dao;
import com.haojing.pojo.User;
import java.util.List;
public interface UserDao {
List<User> getUserList();
}
接口实现类由原来的UserDaoImpl转为一个Mapper配置文件
<?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.haojing.dao.UserDao">
<!-- id接口方法， resultType 返回类型 -->
<select id="getUserList" resultType="com.haojing.pojo.User">
select * from mybatis.user
</select>
</mapper>
4.单元测试
注意点
报错类型1
org.apache.ibatis.binding.BindingException: Type interface com.haojing.dao.UserDao is not known to the MapperRegistry.
检查mybatis-config文件是否注册了mapper
<mappers>
<mapper resource="com/haojing/dao/UserMapper.xml" />
</mappers>
报错类型2
java.lang.ExceptionInInitializerError
maven配置文件在build中添加resources，防止资源导出失败(最好父项目和module都添加)
<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>
Junit测试
@Test
public void test(){
//获取SqlSession对象
SqlSession sqlSession = MybatisUtils.getSqlSession();
//执行SQL
UserDao userDao = sqlSession.getMapper(UserDao.class);
List<User> list = userDao.getUserList();
for (User user : list) {
System.out.println(user);
}
//关闭获取SqlSession
sqlSession.close();
}
结果
User{id=1, name='张三', pwd='123456'}
User{id=2, name='张三', pwd='123456'}
User{id=3, name='王五', pwd='123456'}
User{id=4, name='赵六', pwd='123456'}
User{id=5, name='李四', pwd='123456'}
总结可能遇到的问题
- 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
- 工具类版本和MySQL版本不对应
