maven使用笔记--在父pom中声明过的jar可以被继承，使子项目不用写版本号由父pom控制

将dependencies放到dependencyManagement中，如下：        

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1. <dependencyManagement>  
2.     <dependencies>  
3.         <dependency>  
4.             <groupId>junit</groupId>  
5.             <artifactId>junit</artifactId>  
6.             <version>4.9</version>  
7.             <scope>test</scope>  
8.         </dependency>  
9.     </dependencies>  
10. </dependencyManagement>  
11.  那么，子模块在使用到junit的时候，只需要声明groupId和artifactId即可，即：
    
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    1. <dependencies>  
    2.     <dependency>  
    3.         <groupId>junit</groupId>  
    4.         <artifactId>junit</artifactId>  
    5.     </dependency>  
    6. </dependencies>