Mybatis的基本使用

MyBatis与Hibernate的区别是前者相对来说更加的灵活，对dba友好，相比来说，hibernate就比较自动化，完美的实现了ORM的思想，但是这里必然是要付出一定的代价的，而且越来越多的公司开始更多的实用mybatis了，所以完全有必要把他学习一下。

首先一切都应当以一个简单的实例开始，那么可以有进行如下简单的几步。

1：建立数据库（数据库名：test）

mysql执行如下的脚本：

DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `username` varchar(255) DEFAULT NULL,
  `password` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of user
-- ----------------------------
INSERT INTO `user` VALUES ('1', 'xuning', 'toor');
INSERT INTO `user` VALUES ('2', '徐宁', 'mmm');

3：写配置文件，这里为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.jdbc.Driver"/>
            <property name="url" value="jdbc:mysql://localhost:3306/test" />
            <property name="username" value="root"/>
            <property name="password" value="********"/>
      </dataSource>
    </environment>
  </environments>
  
  <mappers>
    <mapper resource="com/xuning/mapper/UserMapper.xml"/>
  </mappers>
</configuration>

public class User {
	private int id;
	private String username;
	private String password;
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getUsername() {
		return username;
	}
	public void setUsername(String username) {
		this.username = username;
	}
	public String getPassword() {
		return password;
	}
	public void setPassword(String password) {
		this.password = password;
	}
}

<?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 namespace="com.xuning.mapper.UserMapper">
    <select id="selectUserByID" parameterType="int" resultType="com.xuning.domain.User">
        select * from user where id = #{id}
    </select>
</mapper>

package com.xuning.start;
import java.io.InputStream;
import org.apache.ibatis.io.ResolverUtil.Test;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import com.xuning.domain.User;
public class demon_1 {
	    public static void main(String[] args) {
	    	String resource = "mybatis-config.xml";
		    //使用类加载器加载mybatis的配置文件（它也加载关联的映射文件）
		    InputStream is = Test.class.getClassLoader().getResourceAsStream(resource);
		    //构建sqlSession的工厂
		    SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is);
		    //使用MyBatis提供的Resources类加载mybatis的配置文件（它也加载关联的映射文件）
		    //Reader reader = Resources.getResourceAsReader(resource); 
		    //构建sqlSession的工厂
		    //SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
		    //创建能执行映射文件中sql的sqlSession
		    SqlSession session = sessionFactory.openSession();
		    /**
		     * 映射sql的标识字符串，
		     * me.gacl.mapping.userMapper是userMapper.xml文件中mapper标签的namespace属性的值，
		     * getUser是select标签的id属性值，通过select标签的id属性值就可以找到要执行的SQL
		     */
		    String statement = "com.xuning.mapper.UserMapper.selectUserByID";//映射sql的标识字符串
		    //执行查询返回一个唯一user对象的sql
		    User user = session.selectOne(statement, 1);
		    System.out.println(user.getUsername());
		}
}