使用PlaceHolder，测试碰见的问题

<?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>
    <!-- 配置分页插件 -->
    <plugins>
        <plugin interceptor="com.github.pagehelper.PageHelper">
            <!-- 设置数据库类型 Oracle,Mysql,MariaDB,SQLite,Hsqldb,PostgreSQL六种数据库-->        
            <property name="dialect" value="mysql"/>
        </plugin>
    </plugins>
</configuration>

    @Test
    public void testPageHelper()
    {    //创建一个spring容器
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:spring/applicationContext-*.xml");
        //从spring容器中获得Mapper的代理对象
        TbItemMapper mapper = applicationContext.getBean(TbItemMapper.class);
        //执行查询，并分页
        TbItemExample example = new TbItemExample();
        //分页处理
        PageHelper.startPage(2, 10);
        List<TbItem> list = mapper.selectByExample(example);
        //取商品列表
        for (TbItem tbItem : list) {
            System.out.println(tbItem.getTitle());
        }
        //取分页信息
        PageInfo<TbItem> pageInfo = new PageInfo<>(list);
        long total = pageInfo.getTotal();
        System.out.println("共有商品："+ total);
    }