1、第一个Mybatis程序
思路:搭建环境-->导入Mybatis-->编写代码-->测试!
2、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, 'allen','123456'), (2, '张三', '123456'), (3, '李四', '123890');
搭建项目：
1、新建一个普通的maven项目
2、删除src目录
3、导入Maven依赖
<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java --> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>8.0.19</version> </dependency> <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis --> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.5.4</version> </dependency> <!-- https://mvnrepository.com/artifact/junit/junit --> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.13</version> <scope>test</scope> </dependency>
4、创建一个maven的子模块，mybatis-01
编写mybatis核心配置文件，mybatis-config.xml：
<?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="com.mysql.cj.jdbc.Driver"/> <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useUnicode=true&characterEncoding=utf-8"/> <property name="username" value="root"/> <property name="password" value="li980314"/> </dataSource> </environment> </environments> </configuration>
编写mybatis工具类，MybatisUtils：
package com.allen.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 = null;
static{
try {
//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();
}
}
public static SqlSession getSqlSession(){
return sqlSessionFactory.openSession();
}
}5、编写代码
实体类，User.java:
package com.allen.pojo;
//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;
}
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，UserDao.java:
package com.allen.dao;
import com.allen.pojo.User;
import java.util.List;
public interface UserDao {
List<User> getUserList();
}Mapper映射文件，UserMapper.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"> <!-- namespace="绑定一个dao/mapper接口" --> <mapper namespace="com.allen.dao.UserDao"> <!-- select查询语句 --> <select id="getUserList" resultType = "com.allen.pojo.User"> select * from mybatis.user; </select> </mapper>
在Mybatis核心配置文件mybatis-config.xml的configuration节点下，增加mapper注册配置：
<!-- 每一个Mapper.xml都需要在Mybatis核心配置文件中注册 --> <mappers> <mapper resource="com/allen/dao/UserMapper.xml" /> </mappers>
编写jUnit测试类：
package com.allen.dao;
import com.allen.pojo.User;
import com.allen.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.List;
public class UserDaoTest {
@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();
//方式二：
//List<User> userList = sqlSession.selectList("com.allen.dao.UserDao.getUserList");
for (User user : userList) {
System.out.println(user);
}
//关闭sqlSession
sqlSession.close();
}
}6、测试
可能会遇到的问题java.lang.ExceptionInInitializerError
是因为我们在java文件夹下写了xml文件，maven没法导出，需要在pom.xml文件下配置：
<!-- 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/java</directory> <includes> <include>**/*.properties</include> <include>**/*.xml</include> </includes> <filtering>false</filtering> </resource> </resources> </build>
再次运行项目，查出数据：
