context:component-scan base-package 通配符写法

<context:component-scan base-package="com.*" />

<context:component-scan base-package="com.*.dao" />

<context:component-scan base-package="com.**.dao" />  // “**”标示不确定层包通配

<context:component-scan base-package="com.*dao" /> // “*dao”以dao结尾的包通配