核心配置文件中的标签必须按照固定的顺序：

properties?,settings?,typeAliases?,typeHandlers?,objectFactory?,

objectWrapperFactory?,reflectorFactory?,plugins?,environments?,

databaseIdProvider?,mappers?

1、environments 标签详

	<environments default="development">
		
		<environment
				id="development">
			
			<transactionManager
					type="JDBC"/>
			
			<dataSource type="POOLED"> 
				<property name="driver" value="${jdbc.driver}"/>
				
				<property name="url" value="${jdbc.url}"/>
				
				<property name="username" value="${jdbc.username}"/>
				
				<property name="password" value="${jdbc.password}"/>
			dataSource>
		environment>
		<environment id="test">
			<transactionManager type="JDBC"/>
			<dataSource type="POOLED">
				<property name="driver" value="com.mysql.cj.jdbc.Driver"/>
				<property name="url" value="jdbc:mysql://localhost:3306/ssm?serverTimezone=UTC"/>
				<property name="username" value="root"/>
				<property name="password" value="root"/>
			dataSource>
		environment>
	environments>

2、properties 标签详解

创建 jdbc.properties 配置文件：

jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/ssm?serverTimezone=UTC
jdbc.username=root
jdbc.password=root

引入 properties 文件：

    
	<properties resource="jdbc.properties" />

访问：

测试：

@Test
    public void selectAllUser() {
        List users = userMapper.selectAllUser();
        for (User user : users) {
            System.out.println(user);
        }
        //User{id=1, username='张三', password='123456', age=19, gender='男', email='123456@qq.com'}
        // User{id=3, username='李四', password='123', age=19, gender='男', email='123456@qq.com'}
        // User{id=4, username='张三', password='123456', age=19, gender='男', email='123456@qq.com'}
    }

 结果：

3、typeAliases 标签详解

	<typeAliases>
		
		
		
		
		
		<package name="com.chenyixin.ssm.pojo"/>
 
	typeAliases>

MyBatis 中为 Java 中常用的类型设置了类型别名(别名不区分大小写):

 

 

4、mappers 标签详解

	<mappers>
		
		
		<package name="com.chenyixin.ssm.mapper"/>
	mappers>

它们在target路径中是一致的：