实际项目过程中&＃xff0c;我们的工程往往是多个模块组合在一起&＃xff0c;甚至相互之间也会有依赖关系&＃xff0c;如何管理好这些依赖是一个很重要的技能。
举个简单的场景&＃xff0c;web工程mavenWeb与java工程mavenJava都属于一个项目里的模块&＃xff0c;而且mavenWeb依赖于mavenJava&＃xff0c;通常&＃xff0c;我们会建立一个父pom来管理这样的工程。
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绝大多数时候我都会直接用eclipse插件所提供的快速建maven工程来选择新建web或者java&＃xff0c;但命令还是很重要的。创建过程中遇到了问题&＃xff1a;
mvn archetype:create -DgroupId&＃61;com.changjiang.test -DartifactId&＃61;mavenJava -DpackageName&＃61;com.changjiang.test
但出现报错&＃xff1a;
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-archetype-plugin:2.4:create (default-cli) on project standalone-pom: Unable to pars
e configuration of mojo org.apache.maven.plugins:maven-archetype-plugin:2.4:create for parameter #: Abstract class or interface &＃39;org.apache.maven
.artifact.repository.ArtifactRepository&＃39; cannot be instantiated -> [Help 1]
参照了网上的解决方案&＃xff1a;
* JAVA_HOME没有设置或者设置有误、m2_home设置有误
* 删除/org/apache/maven/plugins/下的maven-archetype-plugin
* archetype:create命令已经过期&＃xff0c;需要使用 archetype:generate 来进行代替&＃xff08;方案可行&＃xff09;
* maven-archetype-plugin 2.3版本的插件有问题&＃xff0c;换其它版本进行创建&＃xff08;方案可行&＃xff09;
于是改用generate替代create(maven版本3.0.5)&＃xff0c;命令行交互mode出现&＃xff0c;选择一些基本信息后&＃xff0c;创建成功&＃xff1a;
mvn archetype:generate -DgroupId&＃61;com.changjiang.test -DartifactId&＃61;mavenJava -DpackageName&＃61;com.changjiang.test
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接着用命令创建一个mavenWeb工程&＃xff1a;
mvn archetype:generate -DgroupId&＃61;com.changjiang.web -DartifactId&＃61;mavenWeb -DpackageName&＃61;com.changjiang.web -DarchetypeArtifactId&＃61;maven-archetype-webapp
其过程与mavenJava类似&＃xff1b;
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接下来&＃xff0c;我们将工程修改符合eclipse要求的结构&＃xff1a;
mvn eclipse:eclipse
&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;
mvn eclipse:eclipse -DwtpVersion&＃61;2.0
导入eclipse。结构如下&＃xff1a;
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如果我们不用一个父pom来管理这两个模块&＃xff0c;那么当mavenWeb需要依赖mavenJava时&＃xff0c;就必须在打包多次&＃xff0c;如果有多个模块&＃xff0c;这个操作就会非常复杂。这里引入pom对这两个模块进行管理。
...
子项目里&＃xff1a;
...
...
这样&＃xff0c;只要在mavenParent中进行mvn install的操作&＃xff0c;它就会对所有的模块进行自动打包处理。
除了子模块的统一入口&＃xff0c;父pom另一个作用就是依赖的遗传&＃xff0c;设置统一的
...
...
子pom中也可以像在父pom中确定依赖的版本。
如果各个子模块之间也有依赖关系&＃xff0c;比如我们提到的这个场景&＃xff0c;mavenWeb依赖于mavenJava&＃xff0c;那么也可以在父pom中用
需要特别注意的是&＃xff0c;父pom中所定义的各种参数&＃xff0c;子pom可以用${}来引用&＃xff0c;但是
---------------------------->
当然&＃xff0c;父pom中的
另外&＃xff0c;对于maven依赖冲突时&＃xff0c;maven有自己的规则来进行排序&＃xff0c;比如同级的相同依赖&＃xff0c;按在pom中出现的先后排序&＃xff1b;不同级的依赖&＃xff0c;就近原则。
如果在继承的过程中&＃xff0c;发现有依赖中部分的依赖不想被继承&＃xff0c;就要用到
...
---------------------------->
在添加诸如spring等的依赖时&＃xff0c;往往会用到一些依赖所依赖的jar包&＃xff0c;这个时候最好能够将已经引用到&＃xff0c;但是没有放到pom中的依赖放到pom中去。可以用mvn dependency:resolve来查询已经依赖的jar包和文件&＃xff1a;
E:\Users\BruceChan\workspace\dev01\mavenParent>mvn dependency:resolve
[INFO] Scanning for projects...
[INFO] ------------------------------------------------------------------------
[INFO] Reactor Build Order:
[INFO]
[INFO] mavenParent
[INFO] mavenJava
[INFO] mavenWeb Maven Webapp
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building mavenParent 1.0
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-dependency-plugin:2.1:resolve (default-cli) &＃64; mavenParent ---
[INFO]
[INFO] The following files have been resolved:
[INFO] antlr:antlr:jar:2.7.7:compile
[INFO] com.fasterxml:classmate:jar:1.3.0:compile
[INFO] dom4j:dom4j:jar:1.6.1:compile
[INFO] junit:junit:jar:4.11:test
[INFO] org.apache.geronimo.specs:geronimo-jta_1.1_spec:jar:1.1.1:compile
[INFO] org.hamcrest:hamcrest-core:jar:1.3:test
[INFO] org.hibernate:hibernate-core:jar:5.1.0.Final:compile
[INFO] org.hibernate.common:hibernate-commons-annotations:jar:5.0.1.Final:compile
[INFO] org.hibernate.javax.persistence:hibernate-jpa-2.1-api:jar:1.0.0.Final:compile
[INFO] org.javassist:javassist:jar:3.20.0-GA:compile
[INFO] org.jboss:jandex:jar:2.0.0.Final:compile
[INFO] org.jboss.logging:jboss-logging:jar:3.3.0.Final:compile
[INFO] xml-apis:xml-apis:jar:1.0.b2:compile
[INFO]
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building mavenJava 1.0
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-dependency-plugin:2.1:resolve (default-cli) &＃64; mavenJava ---
[INFO]
[INFO] The following files have been resolved:
[INFO] antlr:antlr:jar:2.7.7:compile
[INFO] com.fasterxml:classmate:jar:1.3.0:compile
[INFO] dom4j:dom4j:jar:1.6.1:compile
[INFO] junit:junit:jar:4.11:test
[INFO] org.apache.geronimo.specs:geronimo-jta_1.1_spec:jar:1.1.1:compile
[INFO] org.hamcrest:hamcrest-core:jar:1.3:test
[INFO] org.hibernate:hibernate-core:jar:5.1.0.Final:compile
[INFO] org.hibernate.common:hibernate-commons-annotations:jar:5.0.1.Final:compile
[INFO] org.hibernate.javax.persistence:hibernate-jpa-2.1-api:jar:1.0.0.Final:compile
[INFO] org.javassist:javassist:jar:3.20.0-GA:compile
[INFO] org.jboss:jandex:jar:2.0.0.Final:compile
[INFO] org.jboss.logging:jboss-logging:jar:3.3.0.Final:compile
[INFO] xml-apis:xml-apis:jar:1.0.b2:compile
[INFO]
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building mavenWeb Maven Webapp 1.0
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-dependency-plugin:2.1:resolve (default-cli) &＃64; mavenWeb ---
[INFO]
[INFO] The following files have been resolved:
[INFO] antlr:antlr:jar:2.7.7:compile
[INFO] com.changjiang.test:mavenJava:jar:1.0:compile
[INFO] com.fasterxml:classmate:jar:1.3.0:compile
[INFO] dom4j:dom4j:jar:1.6.1:compile
[INFO] javax.servlet:javax.servlet-api:jar:3.1.0:provided
[INFO] junit:junit:jar:4.11:test
[INFO] org.apache.geronimo.specs:geronimo-jta_1.1_spec:jar:1.1.1:compile
[INFO] org.hamcrest:hamcrest-core:jar:1.3:test
[INFO] org.hibernate:hibernate-core:jar:5.1.0.Final:compile
[INFO] org.hibernate.common:hibernate-commons-annotations:jar:5.0.1.Final:compile
[INFO] org.hibernate.javax.persistence:hibernate-jpa-2.1-api:jar:1.0.0.Final:compile
[INFO] org.javassist:javassist:jar:3.20.0-GA:compile
[INFO] org.jboss:jandex:jar:2.0.0.Final:compile
[INFO] org.jboss.logging:jboss-logging:jar:3.3.0.Final:compile
[INFO] xml-apis:xml-apis:jar:1.0.b2:compile
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Reactor Summary:
[INFO]
[INFO] mavenParent ....................................... SUCCESS [1.148s]
[INFO] mavenJava ......................................... SUCCESS [0.216s]
[INFO] mavenWeb Maven Webapp ............................. SUCCESS [0.220s]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.210s
[INFO] Finished at: Thu Aug 25 15:18:28 CST 2016
[INFO] Final Memory: 9M/244M
[INFO] ------------------------------------------------------------------------
---------------------------->
对于平时用到比较多的依赖&＃xff0c;可以整理一个专门的pom来存放这些依赖&＃xff0c;在使用的时候&＃xff0c;直接引用这个pom就可以了。
不过采用这种方式存在依赖性的问题。
这种依赖性的问题&＃xff0c;总体来说就是有共享的信息&＃xff0c;多用依赖&＃xff0c;没有共享的信息&＃xff0c;就用多模块处理。
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