1. Reasons for learning Mybatis
SSM框架：Spring+Springmvc+Mybatis
The code used by Java to manipulate the database through JDBC was too redundant and not concise. Every time you need to create a link, get data, and encapsulate objects...
The Mybatis framework provides automatic encapsulation of objects (detected data) or persistent objects (stored in the database, etc.)
Framework: Code written by others that can achieve some functions
ORMFramework: Object Relation MappingObject Relational Mapping Table-Mapping-Object
- Full mapping: No need to write Sql execution statement, directly manipulate java code, for example: Hibernate
- Semi-mapping: Mybatis needs to write Sql, but Sql is written separately in xml, separated from java code, convenient for maintenance
2、Hello Mybatis
1. Import the jar package first
- Mybatis and dependent packages link MySql database package
2. Configure resource files
- Establish the main configuration file: Configration.xml, responsible for configuring the database and mapping files
<?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>
<!-- 读取配置文件jdbc.properties -->
<properties resource="jdbc.properties"></properties>
<!-- 可以配置多个环境 -->
<environments default="development">
<!-- 具体的数据库环境 -->
<environment id="development">
<transactionManager type="JDBC" />
<!-- 数据连接池 -->
<dataSource type="POOLED">
<!-- value的值要注意，不要写错！ -->
<property name="driver" value="${driverClassName}" />
<property name="url" value="${url}" />
<property name="username" value="${username}" />
<property name="password" value="${password}" />
</dataSource>
</environment>
</environments>
<mappers>
<!-- 需要配置映射文件 -->
<mapper resource="cn\xxxx\domain\ProductMapper.xml" />
</mappers>
</configuration>
-
Establish jdbc.properties: configure database related information
-
Establish the mapping file ProductMapper.xml: configure the relevant information namespace (the fully qualified name of the interface)
id (required to be consistent with the method name)
<?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">
<!--
namespace: 命名空间：要求为接口的完全限定名
id: 要求与方法名字一致
parameterType： 接口中定义方法，参数类型传入
resultType : 表中每一行的结果类型
#{id} 接收方法的参数
-->
<mapper namespace="cn.xxxx.dao.IProductDao">
<select id="findOne" parameterType="long" resultType="cn.xxxx.domain.Product">
select * from Blog where id = #{id}
</select>
</mapper>
3. Supplement the code of the interface implementation class in dao
Write only one method for testing
@Override
public Product findOne(Long id) {
String resource = "Configration.xml";
Reader reader;
try {
//读取配置文件
reader = Resources.getResourceAsReader(resource);
//SqlSession的工厂
SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(reader);
//session： 连接对象
SqlSession session = factory.openSession();
/**
* 映射文件ProductMapper.xml
* 参数1：namespace+id
* 参数2：方法传入的id
* 该方法查询用的是ProductMapper.xml映射关系
*/
Product product = session.selectOne("cn.xxxx.dao.IProductDao.findOne", id);
return product;
} catch (IOException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
4. Write unit tests
3、MybatisUtil
Extract the repetitive part of the above code and use the singleton pattern enumeration to construct MybatisUtil
/**
* @author 53187
* 对重复代码进行抽取
*/
public enum MybatisUtil {
//定义一个枚举的对象
INSTANCE;
//声明一个工厂，只需要一个工厂，在每次加载的时候创建一次
private static SqlSessionFactory factory = null;
static {
try {
factory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("Configration.xml"));
} catch (IOException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
}
//获到SqlSession对象
public SqlSession session(){
return factory.openSession();
}
}
Supplementary CRUD
4. Mapper mapping manager
1. Create a new Mapper package
2. Create a new ProductMapper.java interface under the package
3. Configure the ProductMapper.xml mapping file
5. Configure aliases and set logs
1. Configure alias: It is too troublesome to simplify the fully qualified name in the main configuration file
<typeAliases>xxx
<!-- 单个配置：测试时使用 -->
<typeAlias type="cn.xxxx.domain.Dept" alias="Dept" />
<!-- 包的配置：项目中使用，添加了包之后，类名或类名首字母小写就是别名 -->
<package name="cn.xxxx.domain" />
</typeAliases>
2. Set the log
Some content printed during the execution of the program