Ideas: Original development approach requires programmers to write Dao Dao Dao interfaces and implementation classes
From the first blog of architecture diagram:
SqlSession中封装了对数据库的操作，如：查询、插入、更新、删除等。
通过SqlSessionFactory创建SqlSession，而SqlSessionFactory是通过SqlSessionFactoryBuilder进行创建。
SqlSessionFactoryBuilder用于创建SqlSessionFacoty，SqlSessionFacoty一旦创建完成就不需要SqlSessionFactoryBuilder了，因为SqlSession是通过SqlSessionFactory生产，所以可以将SqlSessionFactoryBuilder当成一个工具类使用，最佳使用范围是方法范围即方法体内局部变量。
SqlSessionFactory是一个接口，接口中定义了openSession的不同重载方法，SqlSessionFactory的最佳使用范围是整个应用运行期间，一旦创建后可以重复使用，通常以单例模式管理SqlSessionFactory。
SqlSession是一个面向用户的接口， sqlSession中定义了数据库操作方法。
每个线程都应该有它自己的SqlSession实例。SqlSession的实例不能共享使用，它也是线程不安全的（因为SqlSession底层对应的是Connection连接）。因此最佳的范围是请求或方法范围。
**
UserDao Interface
**
public interface UserDao {
/**
* 查全部
* @return
*/
public List<User> findAll();
/**
* 保存用户
* @param user
*/
public void save(User user);
/**
* 更新用户
* @param user
*/
public void update(User user);
/**
* 根据id删除用户
* @param id
*/
public void del(Integer id);
}
UserDaoImpl implementation class
Sql statement execution, the query from the database data encapsulated into the User object returning the result set.
Implementation class injection SqlSessionFactory, temporarily injected through the constructor.
SqlSession create a query, update, and other methods, because SqlSession thread-safe.
Perform CRUD methods, SqlSession need to commit and then close.
public class UserDaoImpl implements UserDao {
//所有的方法共用的factory对象,应该是属于应用级别
private SqlSessionFactory sessionFactory;
public UserDaoImpl(SqlSessionFactory sessionFactory) {
this.sessionFactory = sessionFactory;
}
@Override
public List<User> findAll() {
//每一个方法应该获取一个SqlSession对象,用完应该立即关闭,因为线程不安全
SqlSession sqlSession = sessionFactory.openSession();
List<User> userList = sqlSession.selectList("userMapper.findAll");
sqlSession.close();
return userList;
}
//执行增删改，sqlSession需要comnit操作
@Override
public void save(User user) {
SqlSession sqlSession = sessionFactory.openSession();
sqlSession.insert("userMapper.save",user);
sqlSession.commit();
sqlSession.close();
}
@Override
public void update(User user) {
SqlSession sqlSession = sessionFactory.openSession();
sqlSession.update("userMapper.update" , user);
sqlSession.commit();
sqlSession.close();
}
@Override
public void del(Integer id) {
SqlSession sqlSession = sessionFactory.openSession();
sqlSession.delete("userMapper.del",id);
sqlSession.commit();
sqlSession.close();
}
}
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">
<mapper namespace="userMapper">
<select id="findAll" resultType="com.itheima.domain.User">
select * from user
</select>
<insert id="save" parameterType="com.itheima.domain.User">
insert into user values(null ,"${username}",#{password},#{sex},#{address},#{birthday})
</insert>
<update id="update" parameterType="com.itheima.domain.User">
update user set username=#{username},password=#{password},sex=#{sex},address=#{address}
where id = #{id}
</update>
<delete id="del" parameterType="java.lang.Integer">
delete from user where id = #{value}
</delete>
</mapper>
Seen from the architecture of FIG first blog, the total profile SqlMapConfig.xml by <mapper resource = ... /> incorporated XXXMapper.xml mapping file, the program UserMapper.xml namespace + id of the class as a bottom Configuration Map <String, Mapper> sql statement to locate the key, with the object Mapper (which contains sql, resultType, parameterType) as the value stored sql.
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>
<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/mybatisdb_331"/>
<property name="username" value="root"/>
<property name="password" value="root"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="com/itheima/mapper/UserMapper.xml"/>
</mappers>
</configuration>
Test program TestMybatisDao.java
public class TestMybatisDao {
SqlSessionFactory sqlSessionFactory = null;
@Before
public void init(){
InputStream inputStream = this.getClass().getClassLoader().getResourceAsStream("SqlMapConfig.xml");
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
}
@Test
public void testFindAll(){
UserDao userDao = new UserDaoImpl(sqlSessionFactory);
List<User> userList = userDao.findAll();
for (User user : userList) {
System.out.println(user);
}
}
@Test
public void testSave(){
UserDao userDao = new UserDaoImpl(sqlSessionFactory);
User user = new User();
user.setUsername("小明");
user.setPassword("xiaoming");
user.setSex("男");
user.setAddress("北京房山");
user.setBirthday("2018-08-08");
userDao.save(user);
}
}
Dao of traditional development issues:
- Dao implementation class there are a lot of duplicate code
- When you call SqlSession method, the statement of the id ( ie namespace.id , such as userMapper.findAll) hardcoded
- SqlSession method requires incoming parameter is of type Object, that is to say, if the wrong pass parameters, run-time error will not conducive to development