基础：Dao开发

关于

使用Mybatis开发Dao，通常有两个方法，即原始Dao开发方法和Mapper接口开发方法。

原始Dao开发

原始Dao开发方法需要程序员编写Dao接口和Dao实现类。

User.java

public class User {
	
	//属性名和数据库表的字段对应
	private int id;
	private String username;// 用户姓名
	private String sex;// 性别
	private Date birthday;// 生日
	private String address;// 地址
	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 getSex() {
		return sex;
	}
	public void setSex(String sex) {
		this.sex = sex;
	}
	public Date getBirthday() {
		return birthday;
	}
	public void setBirthday(Date birthday) {
		this.birthday = birthday;
	}
	public String getAddress() {
		return address;
	}
	public void setAddress(String address) {
		this.address = address;
	}
	@Override
	public String toString() {
		return "User [id=" + id + ", username=" + username + ", sex=" + sex
				+ ", birthday=" + birthday + ", address=" + address + "]";
	}
}

User.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 namespace="test">

	<!-- 在 映射文件中配置很多sql语句 -->
	<select id="findUserById" parameterType="int" resultType="cn.itcast.mybatis.po.User">
		SELECT * FROM USER WHERE id=#{value}
	</select>
	
	<!-- 根据用户名称模糊查询用户信息，可能返回多条 -->
	<select id="findUserByName" parameterType="java.lang.String" resultType="cn.itcast.mybatis.po.User">
		SELECT * FROM USER WHERE username LIKE '%${value}%'
	</select>
	
	<!-- 添加用户 -->
	<insert id="insertUser" parameterType="cn.itcast.mybatis.po.User">
		<selectKey keyProperty="id" order="AFTER" resultType="java.lang.Integer">
			SELECT LAST_INSERT_ID()
		</selectKey>
		insert into user(username,birthday,sex,address) value(#{username},#{birthday},#{sex},#{address})	
	</insert>
	
	<!-- 删除 用户 -->
	<delete id="deleteUser" parameterType="java.lang.Integer">
		delete from user where id=#{id}
	</delete>
	
	<!-- 根据id更新用户 -->
	<update id="updateUser" parameterType="cn.itcast.mybatis.po.User">
		update user set username=#{username},birthday=#{birthday},sex=#{sex},address=#{address} 
		 where id=#{id}
	</update>
</mapper>

• 需要在SqlMapConfig.xml中添加映射文件。

UserDao.java

public interface UserDao {
	
	//根据id查询用户信息
	public User findUserById(int id) throws Exception;
	
	//根据用户名列查询用户列表
	public List<User> findUserByName(String name) 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;
}

UserDaoImpl.java

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;
	}

	@Override
	public User findUserById(int id) throws Exception {
		SqlSession sqlSession = sqlSessionFactory.openSession();

		User user = sqlSession.selectOne("test.findUserById", id);

		// 释放资源
		sqlSession.close();

		return user;
	}
	
	@Override
	public List<User> findUserByName(String name) throws Exception {
		SqlSession sqlSession = sqlSessionFactory.openSession();

		List<User> list = sqlSession.selectList("test.findUserByName", name);

		// 释放资源
		sqlSession.close();

		return list;
	}

	@Override
	public void insertUser(User user) throws Exception {
		SqlSession sqlSession = sqlSessionFactory.openSession();

		//执行插入操作
		sqlSession.insert("test.insertUser", user);

		// 提交事务
		sqlSession.commit();

		// 释放资源
		sqlSession.close();
	}

	@Override
	public void deleteUser(int id) throws Exception {
		SqlSession sqlSession = sqlSessionFactory.openSession();

		//执行插入操作
		sqlSession.delete("test.deleteUser", id);

		// 提交事务
		sqlSession.commit();

		// 释放资源
		sqlSession.close();
	}
}

1. 实现UserDao接口方法；
2. 注入sqlSessionFactory（构造方法或其他方法注入）到私有属性sqlSessionFactory；
3. 方法体中，通过sqlSession（线程不安全，方法体内）实现数据交互；
   • （“SqlSession sqlSession = sqlSessionFactory.openSession();”会读取相应配置及映射文件内容；）
4. 资源的关闭与释放（最好添加try-catch块？？？）；

测试 UserDaoImplTest.java

public class UserDaoImplTest {

	private SqlSessionFactory sqlSessionFactory;

	// 此方法是在执行testFindUserById之前执行
	@Before
	public void setUp() throws Exception {
		// 创建sqlSessionFactory

		// mybatis配置文件
		String resource = "SqlMapConfig.xml";
		// 得到配置文件流
		InputStream inputStream = Resources.getResourceAsStream(resource);

		// 创建会话工厂，传入mybatis的配置文件信息
		sqlSessionFactory = new SqlSessionFactoryBuilder()
				.build(inputStream);
	}

	@Test
	public void testFindUserById() throws Exception {
		// 创建UserDao的对象
		UserDao userDao = new UserDaoImpl(sqlSessionFactory);

		// 调用UserDao的方法
		User user = userDao.findUserById(1);
		
		System.out.println(user);
	}
}

1. 业务代码中应该先获取配置文件流，并由sqlSessionFactoryBuilder（一次性，方法局部变量）生成sqlSessionFactory对象（共用，应用运行期内）；
2. 用sqlSessionFactory做为参数，创建接口实现类的对象；

   UserDao userDao = new UserDaoImpl(sqlSessionFactory); 多态，向上转型