什么是MyBatis？
MyBatis是支持普通SQL查询，存储过程和高级映射的优秀持久层框架。MyBatis消除了几乎所有的JDBC代码和参数的手工设置以及结果集的检索。MyBatis使用简单的XML或注解用于配置和原始映射，将接口和Java的POJOs（Plan Old Java Objects，普通的Java对象）映射成数据库中的记录。
总体流程
(1)加载配置并初始化
触发条件：加载配置文件
将SQL的配置信息加载成为一个个MappedStatement对象（包括了传入参数映射配置、执行的SQL语句、结果映射配置），存储在内存中。
(2)接收调用请求
触发条件：调用Mybatis提供的API
传入参数：为SQL的ID和传入参数对象
处理过程：将请求传递给下层的请求处理层进行处理。
(3)处理操作请求触发条件：API接口层传递请求过来
传入参数：为SQL的ID和传入参数对象
处理过程：
(A)根据SQL的ID查找对应的MappedStatement对象。
(B)根据传入参数对象解析MappedStatement对象，得到最终要执行的SQL和执行传入参数。
(C)获取数据库连接，根据得到的最终SQL语句和执行传入参数到数据库执行，并得到执行结果。
(D)根据MappedStatement对象中的结果映射配置对得到的执行结果进行转换处理，并得到最终的处理结果。
(E)释放连接资源。
(4)返回处理结果将最终的处理结果返回。
我的第一个Mybatis Demo
1.创建数据库表（User表）
create table Users
(
userId int identity(1,1) primary key,--自动增长
userName varchar(30) NOT NULL ,
password varchar(80) NOT NULL ,
comment varchar(250) NULL DEFAULT NULL
)
select * from Users
2. 创建实体类
package xiangjie.mybatis.model;
/**
* @author 向洁
* 创建实体类User
*/
public class User {
private int userId;
private String userName;
private String password;
private String comment;
public int getUserId() {
return userId;
}
public void setUserId(int userId) {
this.userId = userId;
}
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public String getComment() {
return comment;
}
public void setComment(String comment) {
this.comment = comment;
}
}
3. 定义数据访问接口
package xiangjie.mybatis.interfaces;
import java.util.List;
import xiangjie.mybatis.model.User;
/**
* @author 向洁
* 定义数据访问接口UserDao
*/
public interface UserDao {
public int
insert(User user);
public
int update(User user);
public
int delete(String userName);
public
List<User> selectAll();
public
int countAll();
public
User findByUserName(String userName);
}
4.创建MyBatis映射文件（UserDaoMapper.xml）<?xml version="1.0" encoding="UTF-8" ?>
<mapper namespace="com.mybatis.config.UserDao">
<select id="countAll" resultType="int">
select count(*) c from user;
</select>
<select id="selectAll" resultType="com.mybatis.config.User">
select * from user order by userName asc
</select>
<insert id="insert" parameterType="com.mybatis.config.User">
insert into user(userName,password,comment) values(#{userName},#{password},#{comment})
</insert>
<update id="update" parameterType="com.mybatis.config.User">
update user set userName=#{userName},password=#{password},comment=#{comment}
where userName=#{userName}
</update>
<delete id="delete" parameterType="int">
delete from user where userName=#{userName}
</delete>
<select id="findByUserName" parameterType="String" resultType="com.mybatis.config.User">
select * from user where userName=#{userName}
</select>
</mapper>
5. 创建mybatis配置文件
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
<configuration>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC" />
<dataSource type="POOLED">
<property name="driver" value="com.sql.jdbc.Driver" />
<property name="url" value="jdbc:sql://localhost:8080/hlp?useUnicode=true&characterEncoding=UTF-8&zeroDateTimeBehavior=convertToNull" />
<property name="username" value="sa" />
<property name="password" value="" />
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="com/mybatis/config/UserDaoMapper.xml"/>
</mappers>
</configuration>
6. 编写测试代码
package
org.xiangjie.test;
import java.io.Reader;
import java.util.Iterator;
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 xiangjie.mybatis.interfaces.UserDao;
import xiangjie.mybatis.model.User;
/**
* @author 向洁
* 测试代码类UserDaoTest
*/
public class UserDaoTest {
public void userDaoTest() throws Exception
{
String resource = "MyBatis-Configuration.xml";
Reader reader = Resources.getResourceAsReader(resource);
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build(reader);
SqlSession session = factory.openSession();
UserDao userDao = session.getMapper(UserDao.class);
User user = new User();
user.setUserName("hongye");
user.setPassword("123456");
user.setComment("备注");
userDao.insert(user);
System.out.println("记录条数："+userDao.countAll());
List<User> users = userDao.selectAll();
Iterator<User> iter = users.iterator();
while(iter.hasNext()){
User u = iter.next();
System.out.println("用户名："+u.getUserName()+"密码："+u.getPassword());
}
user.setComment("comment");
userDao.update(user);
User u = userDao.findByUserName("hongye");
System.out.println(u.getComment());
userDao.delete("hongye");
System.out.println("记录条数："+userDao.countAll());
session.commit();
session.close();
}
}
