前言
MyBatis是一个优秀的持久层框架。原生的jdbc操作存在大量的重复性代码（如注册驱动，创建连接，创建statement，结果集检测等）。框架的作用就是把这些繁琐的代码封装。
MyBatis通过XML或者注解的方式将要执行的sql语句配置起来，并通过java对象和sql语句映射成最终执行的sql语句。最终由MyBatis框架执行sql，并将结果映射成java对象并返回。
正文
准备jar包
- mybatis-3.4.6.jar
- mysql-connector-java-5.1.47.jar
mysql数据库为firstdb，表名为xtb,表结构如下
1.新建java project MybatisPro ，项目结构图：
一共五个文件
在src下新建com.domain包，在新建User.java
package com.domain;public class User {private Integer user_id;private String user_name;private String user_sex;private String user_phone;public String toString() {return "User [user_id=" + user_id + ", user_name=" + user_name + ", user_sex=" + user_sex + ", user_phone="+ user_phone + "]";}public String getUser_phone() {return user_phone;}public void setUser_phone(String user_phone) {this.user_phone = user_phone;}public String getUser_sex() {return user_sex;}public void setUser_sex(String user_sex) {this.user_sex = user_sex;}public String getUser_name() {return user_name;}public void setUser_name(String user_name) {this.user_name = user_name;}public Integer getUser_id() {return user_id;}public void setUser_id(Integer user_id) {this.user_id = user_id;}
}在src下新建com.Dao包，然后新建Interface文件，UserMapper.java
package com.Dao;import com.domain.*;public interface UserMapper {public User findUserById(int id) throws Exception;public void insertUser(User user) throws Exception;
}
在src下新建全局配置文件SqlMapConfig.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.jdbc.Driver"/><property name="url" value="jdbc:mysql://localhost:3306/firstdb"/><!--用自己的数据库名字 --><property name="username" value="root"/> <!-- 用自己的用户名密码 --><property name="password" value=""/></dataSource></environment></environments><mappers><mapper resource="UserMapper.xml"/> <!-- 这里配置映射文件 --></mappers>
</configuration>
新建映射配置文件UserMpper.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标签要指定namespace属性，不然会报错，可看做包名-->
<mapper namespace="com.Dao.UserMapper"><select id="findUserById" parameterType="int" resultType="com.domain.User">select * from xtb where user_id = #{id}</select><insert id="insertUser" parameterType="com.domain.User">insert into xtb(user_name,user_sex,user_phone) values(#{user_name},#{user_sex},#{user_phone})</insert>
</mapper>
最后，新建测试类Test.java
package com.test;import java.io.InputStream;
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 com.Dao.UserMapper;
import com.domain.User;public class Test{public static void main(String[] args) throws Exception {testInsertUser();SelectByid();}public static void SelectByid() throws Exception{String resource = "SqlMapConfig.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(inputStream);SqlSession session = factory.openSession();//---------------UserMapper userMapper = session.getMapper(UserMapper.class);User user = userMapper.findUserById(2);System.out.println(user);//--------------session.close();}public static void testInsertUser() throws Exception{String resource = "SqlMapConfig.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(inputStream);SqlSession session = factory.openSession();//---------------------User user = new User();user.setUser_name("lalala");user.setUser_sex("women");user.setUser_phone("0123345");UserMapper mapper = session.getMapper(UserMapper.class);mapper.insertUser(user);session.commit();//----------------------session.close();}
}
运行程序，查看结果：
常见错误解决：
基本上都是UserMapper.xml和接口UserMap.java的对应关系没有配置好，我把UserMapper.xml和UserMap.java拼在一起可以看下自己的配置是否正确：
简单来说就是：接口的包名，类名，参数，返回值分别对应着映射文件的namespace，id，parameterType，resultType。
总结原理：
mybais运用了代理技术，实例化出接口UserMapper的实例，然后通过根据配置文件调用sql.
具体流程：
1.读取配置文件SqlMapConfig.xml 获取连数据库的相关信息
2.有了这些信息就能创建SqlSessionFactory
3.SqlSessionFactory建立SqlSession
4.SqlSession 通过代理创建出UserMapper接口的实例，并从userMapper.xml中读取信息
5.通过userMapper.xml中的信息，执行sql语句
6.返回结果，关闭session
