查看“基础：Dao开发”的源代码

[[category:Mybatis]]

__TOC__
== 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。<br/>

== 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。<br/>
[[File:原始Dao开发.png|300px]]

=== User.java ===
<syntaxhighlight lang="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 + "]";
	}
}
</syntaxhighlight>

=== User.xml ===
<syntaxhighlight lang="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>
</syntaxhighlight>
* 需要在SqlMapConfig.xml中添加映射文件。

=== UserDao.java ===
<syntaxhighlight lang="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;
}
</syntaxhighlight>

=== UserDaoImpl.java ===
<syntaxhighlight lang="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();
		try {
			User user = sqlSession.selectOne("test.findUserById", id);
		} finally{
			session.close();
		}

		return user;
	}
	
	@Override
	public List<User> findUserByName(String name) throws Exception {
		
		SqlSession sqlSession = sqlSessionFactory.openSession();
		try {
			List<User> list = sqlSession.selectList("test.findUserByName", name);
		} finally{
			session.close();
		}

		return list;
	}

	@Override
	public void insertUser(User user) throws Exception {

		SqlSession sqlSession = sqlSessionFactory.openSession();
		try {
			sqlSession.insert("test.insertUser", user);
		} finally{
			session.close();
		}
	}

	@Override
	public void deleteUser(int id) throws Exception {

		SqlSession sqlSession = sqlSessionFactory.openSession();
		try {
			sqlSession.delete("test.deleteUser", id);
			sqlSession.commit();
		} finally{
			session.close();
		}
	}
}
</syntaxhighlight>
# 实现UserDao接口方法；
# 注入sqlSessionFactory（构造方法或其他方法注入）到私有属性sqlSessionFactory；
# 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；）
# 资源的关闭与释放（最好添加try-catch块？？？）；

=== 测试：UserDaoImplTest.java ===
<syntaxhighlight lang="java" line highlight="3,7,23,26">
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);
	}
}
</syntaxhighlight>
# 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）；
# 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

=== 问题 ===
原始Dao开发中存在以下问题：
# 代码重复：Dao实现类的方法体存在重复代码：通过SqlSessionFactory创建SqlSession，调用SqlSession的数据库操作方法
#: <syntaxhighlight lang="java">
	SqlSession sqlSession = sqlSessionFactory.openSession();
	try {
		sqlSession.insert("insertUser", user);
		sqlSession.commit();
	} finally{
		session.close();
	}
</syntaxhighlight>
# 硬编码：调用sqlSession的数据库操作方法需要指定statement的id，这里存在硬编码，不得于开发维护。
#: <syntaxhighlight lang="java">
	sqlSession.insert("insertUser", user);
</syntaxhighlight>

== Mapper动态代理 ==
Mapper接口开发方法只需要程序员编写Mapper接口（相当于Dao接口），由Mybatis框架根据接口定义创建接口的动态代理对象，代理对象的方法体同上边Dao接口实现类方法。<br/>
* （省略了接口实现类，通过反射来实现）

=== 使用规范 ===
Mapper接口开发需要遵循以下规范：
# Mapper.xml文件中的'''namespace'''与mapper接口的'''类路径'''相同。
# Mapper接口'''方法名'''和Mapper.xml中定义的每个'''statement的id'''相同 
# Mapper接口方法的'''输入参数类型'''和mapper.xml中定义的每个sql的'''parameterType'''的类型相同
# Mapper接口方法的'''输出参数类型'''和mapper.xml中定义的每个sql的'''resultType'''的类型相同

[[File:Mapper动态代理.png|300px]]

=== User.java ===
（同上，略）<br/>
# 路径：“cn.itcast.mybatis.po.User”；

=== UserMapper.xml ===
<syntaxhighlight lang="xml" line highlight="5,7,12,17">
<?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="cn.itcast.mybatis.mapper.UserMapper">
	<!-- 根据id获取用户信息 -->
	<select id="findUserById" parameterType="int" resultType="cn.itcast.mybatis.po.User">
		select * from user where id = #{id}
	</select>

	<!-- 自定义条件查询用户列表 -->
	<select id="findUserByUsername" 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) values(#{username},#{birthday},#{sex},#{address})
	</insert>
</mapper>
</syntaxhighlight>
* （需要在SqlMapConfig.xml中添加映射文件）
# namespace 为 UserMapper.java路径（“cn.itcast.mybatis.mapper.UserMapper”）；
# UserMapper.xml 与 UserMapper.java 同名不同后缀，且位于同一路径下；

=== UserMapper.java ===
<syntaxhighlight lang="java" line highlight="3,5,7">
Public interface UserMapper {
	//根据用户id查询用户信息
	public User findUserById(int id) throws Exception;
	//查询用户列表
	public List<User> findUserByUsername(String username) throws Exception;
	//添加用户信息
	public void insertUser(User user)throws Exception; 
}
</syntaxhighlight>
* 路径：“cn.itcast.mybatis.po.User”；
接口定义有如下特点：
# UserMapper.java 与 UserMapper.xml 同名不同后缀，且位于同一路径下；
# ..方法名 与 ...statement的id相同
# ..方法的输入参数类型 与 ...statement的parameterType的类型相同
# ..方法的输出参数类型 与 ...statement的resultType的类型相同

=== 测试 UserMapperTest.java ===
<syntaxhighlight lang="java" line highlight="16,19,21">
Public class UserMapperTest extends TestCase {

	private SqlSessionFactory sqlSessionFactory;
	
	protected void setUp() throws Exception {
		//mybatis配置文件
		String resource = "sqlMapConfig.xml";
		InputStream inputStream = Resources.getResourceAsStream(resource);
        
		//使用SqlSessionFactoryBuilder创建sessionFactory
		sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
	}

	Public void testFindUserById() throws Exception {
		//获取session
		SqlSession session = sqlSessionFactory.openSession();
        
		//获取mapper接口的代理对象
		UserMapper userMapper = session.getMapper(UserMapper.class);
		//调用代理对象方法
		User user = userMapper.findUserById(1);
        
		System.out.println(user);
		//关闭session
		session.close();
	}
    
	@Test
	public void testFindUserByUsername() throws Exception {
		SqlSession sqlSession = sqlSessionFactory.openSession();
        
		UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
		List<User> list = userMapper.findUserByUsername("张");
        
		System.out.println(list.size());
	}
    
	Public void testInsertUser() throws Exception {
		//获取session
		SqlSession session = sqlSessionFactory.openSession();
        
		//获取mapper接口的代理对象
		UserMapper userMapper = session.getMapper(UserMapper.class);
		//要添加的数据
		User user = new User();
		user.setUsername("张三");
		user.setBirthday(new Date());
		user.setSex("1");
		user.setAddress("北京市");
		//通过mapper接口添加用户
		userMapper.insertUser(user);
		//提交
		session.commit();
        
		//关闭session
		session.close();
	}
}
</syntaxhighlight>
# 利用反射来获取接口实现类：
#: '''<syntaxhighlight lang="java">UserMapper userMapper = session.getMapper(UserMapper.class);</syntaxhighlight>'''