mybatis的config文件配置

<?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核心配置文件-->
<configuration>
    <!--引入数据库属性文件-->
    <properties resource="db.properties"/>
    <settings>
        <!--配置log4j日志输出-->
        <setting name="logImpl" value="LOG4J"/>
        <!--使用驼峰命名法转换字段-->
        <setting name= "mapUnderscoreToCamelCase" value="true"/>
    </settings>
    <!--environments配置环境组-->
    <!--default默认环境-->
    <environments default="development">
        <!--environment单个环境-->
        <environment id="development">
            <!--transactionManager配置事务管理器-->
            <transactionManager type="JDBC"/>
            <!--配置连接池-->
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
    <!--每一个Mapper.XML都需要在mybatis核心配置文件中注册-->
    <mappers>
<!--        <mapper resource="com/rui/dao/UserMapper.xml"/>-->
        <package name="com.chen.dao"/>
    </mappers>
</configuration>