1. When you have a set of projects that inherits a common parent it's possible to put all information about the dependency in the common POM and have simpler references to the artifacts in the child POMs.
把子module中共用部分的jar包都考虑放在parent的dependencyManagement中
2. control the versions of artifacts used in transitive dependencies
优先级：当前dependencyManagement>当前dependency>父dependencyManagement>当前dependency的dependency
3. denpendencyManagement 与 depencencies区别
depencencies 即使在子项目中不写该依赖，仍然会从父项目中继承
denpendencyManagement是偏自由的，子项目要想使用必须自己声明，不然不会引入。denpendencyManagement的好处就是子项目在引入的时候可以不写version使用默认的，当然也可以选择用新的version从而覆盖父项目定义的。