maven 继承关系和聚合

maven继承管理 让版本的管理只在一个地方改变

modules用于聚合，把执行的项目都放到同一的地方用module包括，可以省去一个个项目去mvn install,这样可以所有项目一次聚合 mvn install

传递性依赖原则：

A-->B
A-->C

1.路径最近者优先
2.路径相同，第一声明者优先

注意：
1.dependencyManagement中定义的依赖子module不会共享
2.dependencies中定义的依赖子module可以共享

dependencyManagement的使用 就是方便管理版本,子项目中要引入group id和atifact id

在parent项目的pom.xml配置

 <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
   <modelVersion>4.0.0</modelVersion>

   <groupId>cn.itcast.maven</groupId>
   <artifactId>Parent</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <packaging>pom</packaging>

   <name>Parent</name>
   <url>http://maven.apache.org</url>
 <!--聚合-->
   <modules>
       <module>../Hello</module>
       <module>../HelloFriend</module>
       <module>../MakeFriends</module>
       <module>../Web</module>
 </modules>

   <properties>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
   </properties>

 <!--定义了依赖的关系，让其他项目继承这些包，不用写版本，同一控制了-->
   <dependencyManagement>

   <dependencies>
     <dependency>
       <groupId>junit</groupId>
       <artifactId>junit</artifactId>
       <version>4.9</version>
       <scope>test</scope>
     </dependency>
     <dependency>
             <groupId>cn.itcast.maven</groupId>
             <artifactId>Hello</artifactId>
             <version>0.0.1-SNAPSHOT</version>
             <scope>compile</scope>
         </dependency>
     <dependency>
       <groupId>cn.itcast.maven</groupId>
       <artifactId>HelloFriend</artifactId>
       <version>0.0.1-SNAPSHOT</version>
     </dependency>
     <dependency>
       <groupId>cn.itcast.maven</groupId>
       <artifactId>MakeFriends</artifactId>
       <version>0.0.1-SNAPSHOT</version>
     </dependency>
   </dependencies>
   </dependencyManagement>

  <distributionManagement>
     <repository>
         <id>releases</id>
         <name>Internal Releases</name>
         <url>http://localhost:8080/nexus-2.1.2/content/repositories/releases/</url>
     </repository>
     <snapshotRepository>
         <id>snapshots</id>
         <name>Internal Snapshots</name>
         <url>http://localhost:8080/nexus-2.1.2/content/repositories/snapshots/</url>
     </snapshotRepository>
   </distributionManagement>

 </project>

Hello.pom

 <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
   <modelVersion>4.0.0</modelVersion>

   <artifactId>Hello</artifactId>

   <parent>
           <groupId>cn.itcast.maven</groupId>
      <artifactId>Parent</artifactId>
       <version>0.0.1-SNAPSHOT</version>
         <relativePath>../Parent/pom.xml</relativePath>
 </parent>
 <dependencies>
 <!--不用写版本了  parent那里同一控制了-->
     <dependency>
             <groupId>junit</groupId>
             <artifactId>junit</artifactId>
         </dependency>
 </dependencies>

 </project>

HelloFriend  pom.xml

 <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
   <modelVersion>4.0.0</modelVersion>

   <artifactId>HelloFriend</artifactId>

   <name>HelloFriend</name>

     <parent>
           <groupId>cn.itcast.maven</groupId>
      <artifactId>Parent</artifactId>
       <version>0.0.1-SNAPSHOT</version>
         <relativePath>../Parent/pom.xml</relativePath>
   </parent>
   <dependencies>
     <dependency>
       <groupId>junit</groupId>
       <artifactId>junit</artifactId>
     </dependency>
     <dependency>
             <groupId>cn.itcast.maven</groupId>
             <artifactId>Hello</artifactId>
     </dependency>
     </dependencies>
 </project>