SqlMapConfig.xml配置文件约束

<?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>
    <!--引入外部文件-->
    <properties resource="jdbcConfig.properties"></properties>
    <!--开启二级缓存-->
    <settings>
        <setting name="cacheEnabled" value="true"/>
    </settings>
    <!--配置别名-->
    <typeAliases>
        <package name="com.xl.domain"></package>
    </typeAliases>
    <!--配置环境-->
    <environments default="mysql">
        <environment id="mysql">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}"></property>
                <property name="url" value="${jdbc.url}"></property>
                <property name="username" value="${jdbc.username}"></property>
                <property name="password" value="${jdbc.password}"></property>
            </dataSource>
        </environment>
    </environments>
    <!--指定有注解的dao接口所在位置-->
    <mappers>
        <package name="com.xl.dao"></package>
    </mappers>
</configuration>