Mybatis-Lesson1

http://www.mybatis.cn/

这个网站的内容很有意思，值得收藏！

MyBatis原名iBatis

2010年从Apache迁移到了Google

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原来的JDBC存在的毛病

SET FOREIGN_KEY_CHECKS=0;

-- ----------------------------
-- Table structure for `orders`
-- ----------------------------
DROP TABLE IF EXISTS `orders`;
CREATE TABLE `orders` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `user_id` int(11) NOT NULL COMMENT '下单用户id',
  `number` varchar(32) NOT NULL COMMENT '订单号',
  `createtime` datetime NOT NULL COMMENT '创建订单时间',
  `note` varchar(100) DEFAULT NULL COMMENT '备注',
  PRIMARY KEY (`id`),
  KEY `FK_orders_1` (`user_id`),
  CONSTRAINT `FK_orders_id` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of orders
-- ----------------------------
INSERT INTO `orders` VALUES ('3', '1', '1000010', '2015-02-04 13:22:35', null);
INSERT INTO `orders` VALUES ('4', '1', '1000011', '2015-02-03 13:22:41', null);
INSERT INTO `orders` VALUES ('5', '10', '1000012', '2015-02-12 16:13:23', null);

-- ----------------------------
-- Table structure for `user`
-- ----------------------------
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `username` varchar(32) NOT NULL COMMENT '用户名称',
  `birthday` date DEFAULT NULL COMMENT '生日',
  `sex` char(1) DEFAULT NULL COMMENT '性别',
  `address` varchar(256) DEFAULT NULL COMMENT '地址',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=27 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of user
-- ----------------------------
INSERT INTO `user` VALUES ('1', '王五', null, '2', null);
INSERT INTO `user` VALUES ('10', '张三', '2014-07-10', '1', '北京市');
INSERT INTO `user` VALUES ('16', '张小明', null, '1', '河南郑州');
INSERT INTO `user` VALUES ('22', '陈小明', null, '1', '河南郑州');
INSERT INTO `user` VALUES ('24', '张三丰', null, '1', '河南郑州');
INSERT INTO `user` VALUES ('25', '陈小明', null, '1', '河南郑州');
INSERT INTO `user` VALUES ('26', '王五', null, null, null);

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class JdbcDemo {
    public static void main(String[] args) {
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;

        try {
            // 加载数据库驱动
            Class.forName("com.mysql.jdbc.Driver");
            // 通过驱动管理类获取数据库链接
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mybatis?characterEncoding=utf-8", "root", "root");
            // 定义sql语句 ?表示占位符
            String sql = "select * from user where username = ?";
            // 获取预处理statement
            preparedStatement = connection.prepareStatement(sql);
            // 设置参数，第一个参数为sql语句中参数的序号（从1开始），第二个参数为设置的参数值
            preparedStatement.setString(1, "王五");
            // 向数据库发出sql执行查询，查询出结果集
            resultSet = preparedStatement.executeQuery();
            // 遍历查询结果集
            while (resultSet.next()) {
                System.out.println(resultSet.getString("id") + "  " + resultSet.getString("username"));
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 释放资源
            if (resultSet != null) {
                try {
                    resultSet.close();
                } catch (SQLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            if (preparedStatement != null) {
                try {
                    preparedStatement.close();
                } catch (SQLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            if (connection != null) {
                try {
                    connection.close();
                } catch (SQLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }
    }
}

毛病

①频繁的连接和释放资源
②硬编码问题（要着改SQL）
③返回结果不好包装处理

---

Mybatis架构

 

1、	mybatis配置SqlMapConfig.xml，此文件作为mybatis的全局配置文件，配置了mybatis的运行环境等信息。mapper.xml文件即sql映射文件，文件中配置了操作数据库的sql语句。此文件需要在SqlMapConfig.xml中加载。
2、	通过mybatis环境等配置信息构造SqlSessionFactory即会话工厂
3、	由会话工厂创建sqlSession即会话，操作数据库需要通过sqlSession进行。
4、	mybatis底层自定义了Executor执行器接口操作数据库，Executor接口有两个实现，一个是基本执行器、一个是缓存执行器。
5、	Mapped Statement也是mybatis一个底层封装对象，它包装了mybatis配置信息及sql映射信息等。mapper.xml文件中一个sql对应一个Mapped Statement对象，sql的id即是Mapped statement的id。
6、	Mapped Statement对sql执行输入参数进行定义，包括HashMap、基本类型、pojo，Executor通过Mapped Statement在执行sql前将输入的java对象映射至sql中，输入参数映射就是jdbc编程中对preparedStatement设置参数。
7、	Mapped Statement对sql执行输出结果进行定义，包括HashMap、基本类型、pojo，Executor通过Mapped Statement在执行sql后将输出结果映射至java对象中，输出结果映射过程相当于jdbc编程中对结果的解析处理过程。

不跟spring整合时需要配置

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>
    <properties resource="jdbc.properties"/>
    <!-- 别名 包以其子包下所有类   头字母大小都行-->
    <typeAliases>
<!--         <typeAlias type="com.itheima.mybatis.pojo.User" alias="User"/> -->
        <package name="com.itheima.mybatis.pojo"/>
    </typeAliases>
    <!-- 和spring整合后 environments配置将废除    -->
    <environments default="development">
        <environment id="development">
            <!-- 使用jdbc事务管理 -->
            <transactionManager type="JDBC" />
            <!-- 数据库连接池 -->
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}" />
                <property name="url"
                    value="jdbc:mysql://localhost:3306/mybatis?characterEncoding=utf-8" />
                <property name="username" value="root" />
                <property name="password" value="root" />
            </dataSource>
        </environment>
    </environments>
    <!-- Mapper的位置  Mapper.xml 写Sql语句的文件的位置 -->
    <mappers>
<!--         <mapper resource="sqlmap/User.xml" class="" url=""/> -->
<!--         <mapper resource="sqlmap/User.xml" class="" url=""/> -->
<!--         <mapper class="com.itheima.mybatis.mapper.UserMapper" /> -->
<!--         <mapper url="" /> -->
        <package name="com.itheima.mybatis.mapper"/>
    </mappers>
</configuration>

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">
<!-- 写Sql语句   -->
<mapper namespace="com.itheima.mybatis.mapper.UserMapper">
    <!-- 通过ID查询一个用户 -->
    <select id="findUserById" parameterType="Integer" resultType="User">
        select * from user where id = #{v}
    </select>
    <!-- //根据用户名称模糊查询用户列表
    #{}    select * from user where id = ？    占位符  ? ==  '五'
    ${}    select * from user where username like '%五%'  字符串拼接
     -->
    <select id="findUserByUsername" parameterType="String" resultType="com.itheima.mybatis.pojo.User">
        select * from user where username like "%"#{haha}"%"
    </select>
    <!-- 添加用户 -->
    <insert id="insertUser" parameterType="com.itheima.mybatis.pojo.User">
        <selectKey keyProperty="id" resultType="Integer" order="AFTER">
            select LAST_INSERT_ID()
        </selectKey>
        insert into user (username,birthday,address,sex) 
        values (#{username},#{birthday},#{address},#{sex})
    </insert>
    <!-- 更新 -->
    <update id="updateUserById" parameterType="com.itheima.mybatis.pojo.User">
        update user 
        set username = #{username},sex = #{sex},birthday = #{birthday},address = #{address}
        where id = #{id}
    </update>
    <!-- 删除 -->
    <delete id="deleteUserById" parameterType="Integer">
        delete from user 
        where id = #{vvvvv}
    </delete>
</mapper>

安照图示内容，需要搞一个session工厂了

import java.io.InputStream;
import java.util.Date;
import java.util.List;

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 org.junit.Test;

import com.itheima.mybatis.pojo.User;

public class MybatisFirstTest {

    //成员变量
    @Test
    public void testMybatis() throws Exception {
        //加载核心配置文件
        String resource = "sqlMapConfig.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        
        //执行Sql语句 命名空间com.itheima.mybatis.mapper.UserMapper
        User user = sqlSession.selectOne("test.findUserById", 10);
        
        System.out.println(user);
    }
    //根据用户名称模糊查询用户列表
    @Test
    public void testfindUserByUsername() throws Exception {
        //加载核心配置文件
        String resource = "sqlMapConfig.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        
        //执行Sql语句 
        List<User> users = sqlSession.selectList("test.findUserByUsername", "五");
        for (User user2 : users) {
            System.out.println(user2);
        }
    }
    //添加用户
    @Test
    public void testInsertUser() throws Exception {
        //加载核心配置文件
        String resource = "sqlMapConfig.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        
        //执行Sql语句 
        User user = new User();
        user.setUsername("何炅");
        user.setBirthday(new Date());
        user.setAddress("sadfsafsafs");
        user.setSex("男");
        int i = sqlSession.insert("test.insertUser", user);
        sqlSession.commit();
        
        System.out.println(user.getId());
        
    }
    //更新用户
    @Test
    public void testUpdateUserById() throws Exception {
        //加载核心配置文件
        String resource = "sqlMapConfig.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        
        //执行Sql语句 
        User user = new User();
        user.setId(29);
        user.setUsername("何炅292929");
        user.setBirthday(new Date());
        user.setAddress("222222sadfsafsafs");
        user.setSex("女");
        int i = sqlSession.update("test.updateUserById", user);
        sqlSession.commit();
    }
    //删除
    @Test
    public void testDelete() throws Exception {
        //加载核心配置文件
        String resource = "sqlMapConfig.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        
        sqlSession.delete("test.deleteUserById", 29);
        sqlSession.commit();
    }
}

Mybatis与Hibernate的区别

Mybatis不完全是一个ORM框架，因为MyBatis需要程序员自己编写Sql语句。

Mybatis学习门槛低，简单易学。

Mybatis无法做到数据库无关性，如果需要实现支持多种数据库的软件则需要自定义多套sql映射文件，工作量大。

---

dao层开发与测试（反面教材，自己写实现类）

import com.itheima.mybatis.pojo.User;

public interface UserDao {
    //通过用户ID查询一个用户
    public User selectUserById(Integer id);
}

import java.util.List;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import com.itheima.mybatis.pojo.User;

public class UserDaoImpl implements UserDao {

    //注入
    private SqlSessionFactory sqlSessionFactory;
    public UserDaoImpl(SqlSessionFactory sqlSessionFactory) {
        this.sqlSessionFactory = sqlSessionFactory;
    }
    
    //通过用户ID查询一个用户
    public User selectUserById(Integer id){
        SqlSession sqlSession = sqlSessionFactory.openSession();
        return sqlSession.selectOne("test.findUserById", id);
    }
    
    //通过用户名称模糊查询
    public List<User> selectUserByUsername(Integer id){
        SqlSession sqlSession = sqlSessionFactory.openSession();
        return sqlSession.selectList("test.findUserById", id);
    }
    
}

注意这个before方法，用得很好！

import java.io.InputStream;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;
import com.itheima.mybatis.dao.UserDao;
import com.itheima.mybatis.dao.UserDaoImpl;
import com.itheima.mybatis.pojo.User;

public class MybatisDaoTest {

    public SqlSessionFactory sqlSessionFactory;
    @Before
    public void before() throws Exception {
        //加载核心配置文件
        String resource = "sqlMapConfig.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
    }
    @Test
    public void testDao() throws Exception {
        
        UserDao userDao = new UserDaoImpl(sqlSessionFactory);
        
        User user = userDao.selectUserById(10);
        System.out.println(user);
    }
}

---

mapper取代dao

import com.itheima.mybatis.pojo.User;

public interface UserMapper {

    //遵循四个原则
    //接口 方法名  == User.xml 中 id 名
    //返回值类型  与  Mapper.xml文件中返回值类型要一致
    //方法的入参类型 与Mapper.xml中入参的类型要一致
    //命名空间 绑定此接口
    public User findUserById(Integer id);
    
}

注意关注/理解一下接口与实现类

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 org.junit.Test;
import com.itheima.mybatis.mapper.UserMapper;
import com.itheima.mybatis.pojo.User;

public class MybatisMapperTest {

    @Test
    public void testMapper() throws Exception {
        //加载核心配置文件
        String resource = "sqlMapConfig.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        
        //SqlSEssion帮我生成一个实现类  （给接口）
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        
        User user = userMapper.findUserById(10);
        System.out.println(user);
    }
}

---

关于sqlMapConfig.xml文件

properties（属性）
settings（全局配置参数）
typeAliases（类型别名）
typeHandlers（类型处理器）
objectFactory（对象工厂）
plugins（插件）
environments（环境集合属性对象）
environment（环境子属性对象）
transactionManager（事务管理）
dataSource（数据源）
mappers（映射器）

---