1. 有了hibernate为什么要使用mybatis
Hibernate: 是一个标准的 ORM 框架（对象关系映射）。学习成本较高，不需要编写sql语句，SQL语句自动生成。对于sql语句的优化，修改比较困难。
应用场景：
适合用于sql语句简单的，效率要求不是特别高的项目。
Mybatis: 专注于sql语句，对象映射和输入输出，都由框架帮你完成，所以属于半 ORM系统，
适用场景：
sql语句逻辑复杂，效率要求特别高的应用。
2. mybatis结构图
Snip20180910_14.png
3. helloMybatis
3.1下载mybatis包
https://github.com/mybatis/mybatis-3/releases
然后导包
3.2书写pojo的User
User
/**
*
*/
private static final long serialVersionUID = 1L;
private Integer id;
private String username;// 用户姓名
private String sex;// 性别
private String address;// 地址
@Override
public String toString() {
return "User{" +
"id=" + id +
", username='" + username + '\'' +
", sex='" + sex + '\'' +
", address='" + address + '\'' +
'}';
}
public static long getSerialVersionUID() {
return serialVersionUID;
}
public Integer getId() {
return id;
}
public void setId(Integer 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 String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
}
3.3 书写mapper接口，接口方法需要遵循四个原则
public interface UserMapper {
//遵循四个原则
//1.接口 方法名 == User.xml 中 id 名
//2.返回值类型 与 Mapper.xml文件中返回值类型要一致
//3.方法的入参类型 与Mapper.xml中入参的类型要一致
//4.命名空间 绑定此接口
public User findUserById(Integer id);
public User findUserByUsername(String username);
public Integer insertUser(User user);
public void updateUser(User user);
public void deleteUserById(int i);
}
3.4 书写UserMapper.xml配置文件
<?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="mapper.UserMapper">
<!-- 通过ID查询一个用户 -->
<select id="findUserById" parameterType="Integer" resultType="pojo.User">
select * from user where id = #{v};
</select>
<!-- //根据用户名称模糊查询用户列表
#{} select * from user where id = ？ 占位符 ? == '五'
${} select * from user where username like '%五%' 字符串拼接
-->
<select id="findUserByUsername" parameterType="String" resultType="pojo.User">
select * from user WHERE username LIKE "%"#{v}"%";
</select>
<insert id="insertUser" parameterType="pojo.User">
// 返回插入数据的id
<selectKey keyProperty="id" resultType="Integer" order="AFTER">
SELECT LAST_INSERT_ID();
</selectKey>
INSERT INTO user (username, address, sex) VALUES (#{username}, #{address}, #{sex});
</insert>
<update id="updateUser" parameterType="pojo.User">
UPDATE user
SET username = #{username}, address = #{address}, sex = #{sex} WHERE id = #{id};
</update>
<delete id="deleteUserById" parameterType="Integer">
DELETE FROM user WHERE id = #{id}
</delete>
</mapper>
3.5 测试UserMapperTest
public class UserMapperTest {
@Test
public void findUserById() throws IOException {
//加载核心配置文件
String resource = "sqlMapConfig.xml";
InputStream in = Resources.getResourceAsStream(resource);
//创建SqlSessionFactory
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
//创建SqlSession
SqlSession sqlSession = sqlSessionFactory.openSession();
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
User user = userMapper.findUserById(1);
System.out.println(user);
}
@Test
public void testFindUserByUsername() throws IOException {
//加载核心配置文件
String resource = "sqlMapConfig.xml";
InputStream in = Resources.getResourceAsStream(resource);
//创建SqlSessionFactory
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
//创建SqlSession
SqlSession sqlSession = sqlSessionFactory.openSession();
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
System.out.println(userMapper.findUserByUsername("张污"));
}
@Test
public void insertUser() throws IOException {
//加载核心配置文件
String resource = "sqlMapConfig.xml";
InputStream in = Resources.getResourceAsStream(resource);
//创建SqlSessionFactory
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
//创建SqlSession
SqlSession sqlSession = sqlSessionFactory.openSession();
User user = new User();
user.setUsername("阿珍");
user.setAddress("北京");
user.setSex("男");
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
userMapper.insertUser(user);
sqlSession.commit();
// 用户保存好之后，获取到用户的id进行其他的后续操作
System.out.println(user.getId());
}
@Test
public void updateUserById() throws IOException {
//加载核心配置文件
String resource = "sqlMapConfig.xml";
InputStream in = Resources.getResourceAsStream(resource);
//创建SqlSessionFactory
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
//创建SqlSession
SqlSession sqlSession = sqlSessionFactory.openSession();
User user = new User();
user.setId(1);
user.setUsername("张三");
user.setAddress("北京33");
user.setSex("男33");
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
userMapper.updateUser(user);
sqlSession.commit();
}
@Test
public void deleteUserById() throws IOException {
//加载核心配置文件
String resource = "sqlMapConfig.xml";
InputStream in = Resources.getResourceAsStream(resource);
//创建SqlSessionFactory
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
//创建SqlSession
SqlSession sqlSession = sqlSessionFactory.openSession();
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
userMapper.deleteUserById(3);
sqlSession.commit();
}
}
4.问题
4.1 关于模糊查询时，中文查不到结果的问题
要将数据库设置成UTF-8的编码
<property name="driver" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://123.206.7.239/xiaobang?characterEncoding=UTF-8" />
