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

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
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

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
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/
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