MyBatis开发dao方法

一 SqlSession使用范围

• SqlSessionFactoryBuilder
  • 通过SqlSessionFactoryBuilder创建会话工厂SqlSessionFactory
  • 将SqlSessionFactoryBuilder当作一个工具类使用即可，不需要使用单例管理SqlSessionFactoryBuilder。
  • 在需要创建SqlSessionFactory时候，只需要new一次SqlSessionFactoryBuilder 即可
• SqlSessionFactory
  • 通过SqlSessionFactory创建SqlSession使用单例模式管理SqlSessionFactory(工厂一旦创建，使用一个实例)
  • 将来mybatis和spring整合后使用单例模式管理sqlSessionFactory
• SqlSession
  • SqlSession是一个面向用户（程序员）的接口
  • SqlSession中提供了很多操作数据库的方法，例如：selectOne/selectList
  • sqlSession是线程不安全的，在SqlSession实现类中除了有接口中的方法（操作数据库的方法）还有ukulel域属性
  • SqlSession最佳应用场合在方法体内，定义成局部变量使用

二 mybatis开发dao方法-原始dao开发方法-程序员需要写dao接口和dao实现类

1 UserDao.java

package dao;

import entity.User;

public interface UserDao {
    //根据id查询信息
    public User findUserById(int id) throws Exception;
    //添加用户信息
    public void insertUser(User user) throws Exception;
    //删除用户信息
    public void deleteUser(int id) throws Exception;
}

2 UserDaoImpl.java

package dao.impl;

import dao.UserDao;
import entity.User;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;

import java.util.Date;

public class UserDaoImpl implements UserDao {
    //需要向dao实现类中注入SqlSessionFactory
        //这里通过构造方法注入
    private SqlSessionFactory sqlSessionFactory;
    public UserDaoImpl(SqlSessionFactory sqlSessionFactory){
        this.sqlSessionFactory = sqlSessionFactory;
    }


    public User findUserById(int id) throws Exception {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        User user = sqlSession.selectOne("test.findUserById",id);
        sqlSession.close();
        return user;
    }
    public void insertUser(User user) throws Exception {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        sqlSession.insert("test.insertUser",user);
        sqlSession.commit();
        sqlSession.close();
    }
    public void deleteUser(int id) throws Exception {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        sqlSession.delete("test.deleteUser",id);
        sqlSession.commit();
        sqlSession.close();
    }
}

3 UserDaoImplTest.java

import dao.UserDao;
import dao.impl.UserDaoImpl;
import entity.User;
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 java.io.IOException;
import java.io.InputStream;
import java.util.Date;

public class UserDaoImplTest {
    private SqlSessionFactory sqlSessionFactory;
    //测试前执行    
@Before
    public void setUp() throws IOException {
        //配置文件
        String resource = "SqlMapConfig.xml";
        //的到配置文件流
        InputStream inputStream =  Resources.getResourceAsStream(resource);
        //创建会话工厂
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    }
    @Test
    public void testFinUserById() throws Exception {
        UserDao userDao = new UserDaoImpl(sqlSessionFactory);
        User user = userDao.findUserById(1);
        System.out.println(user);
    }
    @Test
    public void insertUser() throws Exception{
        UserDao userDao = new UserDaoImpl(sqlSessionFactory);
        User user1 = new User();
        user1.setUsername("王麻子");
        user1.setBirthday(new Date());
        user1.setSex("女");
        user1.setAddress("日本东京");
        userDao.insertUser(user1);
    }
    @Test
    public void deleteUser() throws Exception{
        UserDao userDao = new UserDaoImpl(sqlSessionFactory);
        userDao.deleteUser(13);
    }
}

查询测试结果

三 mybatis开发dao方法-mapper代理开发方法-程序员只需要mapper接口（相当于dao接口）

• 程序员不在需要编写dao接口的实现
• 程序员需要编写mapper.xml映射文件，编写时遵循一些开发规范，mybatis可以自动生成mapper接口类代理对象

1 开发规范

（1）在mapper.xml中namespace等于mapper接口地址

（2）mapper.java接口中的方法名和mapper.xml中statement的id一致

（3）mapper.java接口中的方法输入类型和mapper.xml中statement的parameterType指定的类型一致

（4）mapper.java接口中方法返回值类型和mapper.xml中statement的resultType指定的类型一致

2 UserDaoMapper.java

package dao;

import entity.User;

public interface UserDaoMapper {
    //根据id查询
    public User findUserById(int id) throws Exception;
    //插入用户
    public void insertUser(User user) throws Exception;
    //删除用户
    public void deleteUser(int id) throws Exception;
    //修改用户信息
    public void updateUser(User user) throws Exception;
}

3 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命名空间，作用就是对sql进行分类化管理，区分不同的sql空间
        注意：使用mapper代理方法开发，namespace有特殊重要作用-->
<mapper namespace="dao.UserDaoMapper">
    <!--在映射文件中配置很多sql语句-->
   <!-- 需求：通过id查询用户表的记录-->
 <!--   通过select执行数据库查询
    id：标识映射文件中sql，将sql语句封装到mappedStatement对象中，所以将id称为statement的id
    parameterType：指定输入参数的类型，这里指定int型
    resultType:指定sql输出结果所映射的java对象类型
    #{ }表示一个占位符
    #{id}：其中的id表示接收输入的参数，参数名称就是id-->
    <select id="findUserById" parameterType="int" resultType="entity.User">
    SELECT * FROM user WHERE id = #{id}
</select>
    <!--根据用户名称模糊查询信息-->
    <!--可能返回多条信息
    ${}：表示拼接sql串，将接收到的参数的内容不加任何修饰拼接在sql中
    使用${}拼接sql，引起sql注入
    ${value}：接收输入参数的内容，如果出入类型是简单类型，${}只能使用value-->
    <select id="findUserByName" parameterType="String" resultType="entity.User">
        SELECT * FROM  user WHERE username LIKE "${value}%"
    </select>
    <!--添加用户-->
    <insert id="insertUser" parameterType="entity.User">
        <!--将插入数据的主键返回
        SELECT Last_insert_ID 得到刚插入的主键值 只适用与自增主键

        keyProperty :将查询到主键值设置到parameterType指定的对象的那个属性
        order:SELECT Last_insert_ID执行顺序，相对于insert语句来说它的执行顺序
        resultType:指定SELECT LAST_INSERT_ID()的结果类型
        -->
        <selectKey keyProperty="id" order="AFTER" resultType="int">
            SELECT LAST_INSERT_ID()
        </selectKey>
        INSERT INTO user (username,birthday,sex,address) VALUES(#{username},#{birthday},#{sex},#{address})
    </insert>
    <!--删除用户 通过id-->
    <delete id="deleteUser" parameterType="int">
        DELETE from user where id = #{id}
    </delete>
    <!--修改用户信息 根据id-->
    <update id="updateUser" parameterType="entity.User">
        UPDATE user SET username = #{username},birthday = #{birthday},sex = #{sex},address = #{address} WHERE  id = #{id}
    </update>
</mapper>

4 UserDaoMapperTest

import dao.UserDaoMapper;
        import entity.User;
        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.Before;
        import org.junit.Test;


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

public class UserDaoMapperTest {
    private SqlSessionFactory sqlSessionFactory;
    @Before
    public void setUp() throws IOException{
        String resource = "SqlMapConfig.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    }
    @Test
    public void findUserById() throws Exception{
        SqlSession sqlSession= sqlSessionFactory.openSession();
        //创建UserMapper对象，mybatis自动生成mapper代理对象
        UserDaoMapper userDaoMapper = sqlSession.getMapper(UserDaoMapper.class);
        //调用usermapper对象
        User user = userDaoMapper.findUserById(10);
        System.out.println(user);
    }
    @Test
    public void insertUserd() throws Exception{
        SqlSession sqlSession= sqlSessionFactory.openSession();
        //创建UserMapper对象，mybatis自动生成mapper代理对象
        UserDaoMapper userDaoMapper = sqlSession.getMapper(UserDaoMapper.class);
        //调用usermapper对象
        User user = new User();
        user.setUsername("短毛");
        user.setBirthday(new Date());
        user.setSex("女");
        user.setAddress("德国柏林");
        userDaoMapper.insertUser(user);
        sqlSession.commit();
        sqlSession.close();
    }
    @Test
    public void deleteUser() throws Exception {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        UserDaoMapper userDaoMapper = sqlSession.getMapper(UserDaoMapper.class);
        userDaoMapper.deleteUser(13);
        sqlSession.commit();
        sqlSession.close();
    }
    @Test
    public void updateUser() throws Exception{
    SqlSession sqlSession = sqlSessionFactory.openSession();
    UserDaoMapper userDaoMapper = sqlSession.getMapper(UserDaoMapper.class);
        User user = new User();
        user.setId(12);
        user.setUsername("短毛");
        user.setBirthday(new Date());
        user.setSex("女");
        user.setAddress("德国柏林");
    userDaoMapper.updateUser(user);
    sqlSession.commit();
    sqlSession.close();
    }

}

查询执行结果