Build - Maven
What is Maven
Maven is a build automation tool used primarily for Java projects.
Features
- Making the build process easy
- Providing a uniform build system
- Providing quality project information
- Providing guidelines for best practices development
- Allowing transparent migration to new features
Concept
Repository
- Local Repository: a folder location on your machine.
- Central Repository: This repository is managed by Maven community.
- Remote Repository: user defined, see below example.
<project>
<repositories>
<repository>
<id>companyname.lib1</id>
<url>http://download.companyname.org/maven2/lib1</url>
</repository>
</repositories>
</project>
Search sequence: local repository -> central repository -> remote repository
Phase
Build LifeCycle
- validate: validate the project is correct and all necessary information is available
- compile: compile the source code of the project
- test: test the compiled source code using a suitable unit testing framework. These tests should not require the code be packaged or deployed
- package: take the compiled code and package it in its distributable format, such as a JAR.
- verify: run any checks on results of integration tests to ensure quality criteria are met
- install: install the package into the local repository, for use as a dependency in other projects locally
- deploy: done in the build environment, copies the final package to the remote repository for sharing with other developers and projects.
一种实践是，在本地执行package，打好包，手动上传到服务器上，再启动程序。
Build
Add Dependency
in pom.xml, add:
<dependencies>
...
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>4.1.6.RELEASE</version>
</dependency>
</dependencies>
Plugin
作用：在整个build的lifeCycle之间，插入一些job，做一些其它的工作。
以下示例，在package的过程中，加入了一个maven-assembly-plugin，这个插件做的事情是，根据package.xml中的描述，额外地做一些打包工作。
<build>
...
<plugins>
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<version>2.2-beta-4</version>
<executions>
<execution>
<id>make-assembly</id>
<phase>package</phase>
<goals>
<goal>attached</goal>
</goals>
</execution>
</executions>
<configuration>
<descriptors>
<descriptor>src/main/assembly/package.xml</descriptor>
</descriptors>
</configuration>
</plugin>
<plugins>
</build>
- http://maven.apache.org/plugins/maven-assembly-plugin
Cmd
~~~ shell mvn clean install -e -U
-e 详细异常 -U 强制更新
https://blog.csdn.net/yiguoxiaohai/article/details/125708088
## Dependency Conflict
依赖冲突 问题：项目中，A有两个dependency，但是C的version在两个地方配置得不一样，如下。那么，实际生效的C的version是哪个呢？
A -> B -> C (v1) A -> C (v2)
规则
- 短路优先；在上例中，C是v2。
- （相同路径的情况下）先声明优先。
另外，如果想要指定一个version，可以在pom中把其它的exlcude掉。
参考以下：
- [Maven依赖传递、依赖传递排除、依赖冲突](https://www.cnblogs.com/ygj0930/p/6628429.html)
- [Maven依赖版本冲突的分析及解决小结](https://www.cnblogs.com/godtrue/p/6220512.html)
## Cyclic Dependency
依赖循环 问题：项目中，`A -> B -> C -> A`，这时编译会报错。怎么解决呢？
如果都是自己部门的项目，可以修改代码，将共同依赖提取出来。如下：
A -> D B -> D C -> D
如果都是第三方类库，这个情况应该不会出现，因为过不了编译，无法发布到线上。
如果一个是自己部门的项目，其余是第三方类库，这个情况也不成立，因为第三方类库不会依赖于私有的项目。
注：网上有说使用`build-helper-maven-plugin`插件解决，感觉像是第一种情况。
## Settings
一个例子
~~~ xml
<!-- 本地仓库的位置，即Maven将下载的依赖项存储在本地的位置 -->
<localRepository>/path/to/local/repo</localRepository>
<!-- 镜像设置，用于指定中央仓库的镜像，以提高依赖项下载的速度 -->
<mirrors>
<mirror>
<id>mirrorId</id>
<name>mirrorName</name>
<url>http://mirror.example.com/maven2/</url>
<mirrorOf>central</mirrorOf>
</mirror>
</mirrors>
<!-- 代理服务器设置，如果您需要使用代理服务器来访问互联网，则可以在此处进行配置 -->
<proxies>
<proxy>
<id>proxyId</id>
<active>true</active>
<protocol>http</protocol>
<host>proxy.example.com</host>
<port>8080</port>
<username>proxyUsername</username>
<password>proxyPassword</password>
<nonProxyHosts>localhost|*.example.com</nonProxyHosts>
</proxy>
</proxies>
<!-- Profile设置，可根据需要创建多个Profile进行不同的配置 -->
<profiles>
<!-- development Profile，设置为默认Profile -->
<profile>
<id>development</id>
<activation>
<activeByDefault>true</activeByDefault>
</activation>
<properties>
<environment>dev</environment>
</properties>
</profile>
<!-- production Profile -->
<profile>
<id>production</id>
<properties>
<environment>prod</environment>
</properties>
</profile>
</profiles>
https://blog.csdn.net/hlzdbk/article/details/129822239
Cheat Cheet
check version
mvn --version
create a project
mvn archetype:generate
build the project
mvn package
run
java -cp target/***.jar classpath.ClassName
(if you use other packages, you need to set their cp in the cmd)
run Java main from Maven
mvn exec:java -Dexec.mainClass="com.vineetmanohar.module.Main"
mvn exec:java -Dexec.mainClass="com.vineetmanohar.module.Main" -Dexec.args="arg0 arg1 arg2"
