Maven settings.xml配置解读

请确保自己的maven环境安装成功，具体安装流程详见Maven安装

在安装完maven环境后，最重要的就是去配置settings.xml文件，其作为统一的依赖配置管理入口，了解其相关配置有助于我们对maven的理解

settings.xml主配置文件

笔者此处优先查看其注释内容，信息如下

<!--
 | This is the configuration file for Maven. It can be specified at two levels:
 |  #用户级别，面向单个用户配置，即每个用户都可以自定义settings.xml供己方使用
 |  1. User Level. This settings.xml file provides configuration for a single user,
 |                 and is normally provided in ${user.home}/.m2/settings.xml.
 |
 |  #其中的CLI选项指的是mvn操作命令的相关参数比如：mvn -v
 |                 NOTE: This location can be overridden with the CLI option:
 |
 |                 -s /path/to/user/settings.xml
 |  #全局级别，即面向所有用户同一配置
 |  2. Global Level. This settings.xml file provides configuration for all Maven
 |                 users on a machine (assuming they're all using the same Maven
 |                 installation). It's normally provided in
 |                 ${maven.home}/conf/settings.xml.
 |
 |                 NOTE: This location can be overridden with the CLI option:
 |
 |                 -gs /path/to/global/settings.xml
 |
 | The sections in this sample file are intended to give you a running start at
 | getting the most out of your Maven installation. Where appropriate, the default
 | values (values used when the setting is not specified) are provided.
 |
 |-->

由上可得

1. settings.xml具有两个级别：用户级别和全局级别，一般我们只需要去配置用户级别即可
2. settings.xml配置的是所有POM工程项目的全局配置

主要参数配置

笔者罗列出主要的参数配置

	## 此处的构件我们简单的理解为依赖，针对JAVA就是JAR包
	localRepository	本地仓库配置路径
	interactiveMode 是否交互式输入提醒，默认true
	offline	是否每次编译部署时候需要联网，默认false
	pluginGroups 插件组合，供编译时选用
	proxies 代理配置，连接本地无法远程的网络
	servers 服务配置，上传构件/连接仓库所用
	mirrors 替代有网络问题的repository的访问站点
	profiles 应用于不同环境的配置
	activeProfiles 激活指定的配置，与profile搭配使用

对上述的参数分别作下简单的描述，更多的解释可详见官网Maven-Settings Reference

localRepository

本地仓库路径，主要用于存放从远程仓库下载的构件依赖。采用绝对路径，默认存放在${user.home}/.m2/repository路径下

<!-- localRepository
	| The path to the local repository maven will use to store artifacts.
	|
	| Default: ${user.home}/.m2/repository-->

interactiveMode

交互式节点配置，默认为true。设置为false则会在mvn执行中使用默认的参数设置交互性问题

<!-- interactiveMode
   | This will determine whether maven prompts you when it needs input. If set to false,
   | maven will use a sensible default value, perhaps based on some other setting, for
   | the parameter in question.
   |
   | Default: true-->

offline

是否每次的编译部署都需要联网，默认为false。如果构件不需要更新下载则可设置为true，以提高build效率和成功率。

<!-- offline
   | Determines whether maven should attempt to connect to the network when executing a build.
   | This will have an effect on artifact downloads, artifact deployment, and others.
   |
   | Default: false-->

pluginGroups

插件组，默认包含maven插件、mojo插件，用于插件在使用时没有指定groupId时，这个列表就会被搜索。

!-- pluginGroups
   | This is a list of additional group identifiers that will be searched when resolving plugins by their prefix, i.e.
   | when invoking a command line like "mvn prefix:goal". Maven will automatically add the group identifiers
   | "org.apache.maven.plugins" and "org.codehaus.mojo" if these are not already contained in the list.
   |-->

举个例子：

<pluginGroups>
	<pluginGroup>
		org.mortbay.jetty
	</pluginGroup>
</pluginGroups>

上述配置后，可通过mvn jetty run替代长命令org.morbay.jetty:jetty-maven-plugin:run

proxies

网络代理配置

<!-- proxies 
   | This is a list of proxies which can be used on this machine to connect to the network.
   | Unless otherwise specified (by system property or command-line switch), the first proxy
   | specification in this list marked as active will be used.
   |-->
  <proxies>
    <!-- proxy 新增一个代理配置示例
     | Specification for one proxy, to be used in connecting to the network.
     |
    <proxy>
      <id>optional</id>
      <active>true</active>
      <protocol>http</protocol>
      <username>proxyuser</username>
      <password>proxypass</password>
      <host>proxy.host.net</host>
      <port>80</port>
      <nonProxyHosts>local.net|some.host.com</nonProxyHosts>
    </proxy>
    -->
  </proxies>

默认以第一个配置的代理节点作为网络的通信(正向代理)。主要用于解决构件下载不到的问题

servers

上传或者下载构件时所需要验证的服务器配置。通过id来区分，主要与mirror/repository配置搭配使用

有两种方式的校验，此配置有助于用户可以搭建自己的maven私库。

---

密码方式校验(推荐)

 <!-- servers
   | This is a list of authentication profiles, keyed by the server-id used within the system.
   | Authentication profiles can be used whenever maven must make a connection to a remote server.
   |-->
  <servers>
    <!-- server
     | Specifies the authentication information to use when connecting to a particular server, identified by
     | a unique name within the system (referred to by the 'id' attribute below).
     |
     | NOTE: You should either specify username/password OR privateKey/passphrase, since these pairings are
     |       used together.
     |
    <server>
      <id>deploymentRepo</id>
      <username>repouser</username>
      <password>repopwd</password>
    </server>
    -->

---

privateKey方式校验，更为安全的认证方式

  <servers>
    <!-- Another sample, using keys to authenticate.
    <server>
      <id>siteServer</id>
      <privateKey>/path/to/private/key</privateKey>
      <passphrase>optional; leave empty if not used.</passphrase>
    </server>
    -->
  </servers>

mirrors

构件镜像，替代有网络问题的仓库的访问站点。即当maven构件出现下载问题时便通过此配置替换原有的下载地址去下载

<!-- mirrors
   | This is a list of mirrors to be used in downloading artifacts from remote repositories.
   |
   | It works like this: a POM may declare a repository to use in resolving certain artifacts.
   | However, this repository may have problems with heavy traffic at times, so people have mirrored
   | it to several places.
   |
   | That repository definition will have a unique id, so we can create a mirror reference for that
   | repository, to be used as an alternate download site. The mirror site will be the preferred
   | server for that repository. //central代表maven官网的中央仓库
   |-->

举个例子

	<mirror>
		<!--与server参数配置的id属性一致，登录校验-->
	    <id>${server_id}</id>
		<!--拦截指定的仓库，支持多仓库id，以逗号分隔(*代表拦截所有的仓库,central代表拦截maven官方中央仓库)-->
	    <mirrorOf>${repository_id}/*</mirrorOf>
	    <name>Human Readable Name for this Mirror.</name>
		<!--服务器地址-->
	    <url>http://my.repository.com/repo/path</url>#镜像url
	</mirror>

profiles

多条件集合配置，用于不同条件下可应用不同的配置，其中也可配置自定义的repository/pluginRepository。灵活性很高

	| This profile example uses the JDK version to trigger activation, and provides a JDK-specific repo.
    <profile>
      <id>jdk-1.4</id>
	  <!--在此配置的任何一个节点条件满足则触发此配置-->
      <activation>
        <jdk>1.4</jdk>
      </activation>
	  <!--仓库配置-->
      <repositories>
        <repository>
          <id>jdk14</id>#唯一ID，可与server搭配使用
          <name>Repository for JDK 1.4 builds</name>
          <releases>#发布版本
                <enabled>false</enabled> #不允许在发布版本中寻找构件
                <updatePolicy>always</updatePolicy> #检查构件更新的策略
                <checksumPolicy>warn</checksumPolicy>
          </releases>
          <snapshots>#快照版本
                <enabled>true</enabled>#允许在快照版本中寻找构件
                <updatePolicy>never</updatePolicy>
                <checksumPolicy>fail</checksumPolicy>
          </snapshots>
          <url>http://www.myhost.com/maven/jdk14</url>
          <layout>default</layout>
          <snapshotPolicy>always</snapshotPolicy>
        </repository>
      </repositories>
    </profile>

像上述的例子，用户只需要jdk版本大于1.4，上述的profile便会生效。

activeProfiles

与profile参数搭配使用，用于激活相应的profile配置，可激活多个配置

  <activeProfiles>
    <activeProfile>${profile_id1}</activeProfile>
    <activeProfile>${profile_id2}</activeProfile>
  </activeProfiles>

总结

1. server节点是仓库服务器的配置，有密码校验方式和私钥校验方式。其下的id配置应用于mirror/repository节点用于登录校验

2. mirror节点配置会根据其内部的mirrorOf配置拦截指定的repository。
   如果指定为*则会拦截所有的仓库；
   指定为central则会拦截https://repo.maven.apache.org/maven2/

3. profile节点则可由用户灵活配置，可用于不同条件下的环境配置