Mybatis 框架搭建实例

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