mybatis中配置中引入properties文件

<?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properties文件  --> <properties resource="db.properties"></properties><!--和Spring整合后 environments 配置将废除 -->  <environments default="development">    <environment id="development">    <!--使用JDBC事务管理  -->      <transactionManager type="JDBC"/>      <!--数据库连接池  -->      <dataSource type="POOLED">        <property name="driver" value="${jdbc.driverClass}"/>        <property name="url" value="${jdbc.url}"/>        <property name="username" value="${jdbc.username}"/>        <property name="password" value="${jdbc.password}"/>      </dataSource>    </environment>  </environments>  <!--加载xml文件  -->  <mappers>    <mapper resource="mapper/UserMapper.xml"/>  </mappers></configuration>