以前在日常工作中，使用Maven隻是機械的執行Maven clean、Maven install,對其中的原理與過程并無了解，近期閱讀了《Maven實戰》，對Maven有了更深入的了解。
本篇就針對讀書後的了解，對Maven的日常使用相關的知識進行總結與歸納。
如果想要了解更多内容參考：《Maven實戰》
1 什麼是Maven？
如果沒有Maven,你可能不得不經曆下面的過程：
1 如果使用了spring，去spring的官網下載下傳jar包；如果使用hibernate，去hibernate的官網下載下傳Jar包；如果使用Log4j，去log4j的官網下載下傳jar包.....
2 當某些jar包有依賴的時候，還要去下載下傳對應的依賴jar包
3 當jar包依賴有沖突時，不得不一個一個的排查
4 執行建構時，需要使用ant寫出很多重複的任務代碼
5 當新人加入開發時，需要拷貝大量的jar包，然後重複進行建構
6 當進行測試時，需要一個一個的運作....檢查
有了Maven，它提供了三種功能：
1 依賴的管理：僅僅通過jar包的幾個屬性，就能确定唯一的jar包，在指定的檔案pom.xml中，隻要寫入這些依賴屬性，就會自動下載下傳并管理jar包。
2 項目的建構：内置很多的插件與生命周期，支援多種任務，比如校驗、編譯、測試、打包、部署、釋出...
3 項目的知識管理：管理項目相關的其他内容，比如開發者資訊，版本等等
2 Maven如何管理jar包
關于jar包的坐标，有過使用經驗的都應該有所了解，maven是通過groupId，artifactId，以及version确定一個唯一的jar包。
這部分的内容可以參考前一篇：建構過程
例如,最常使用的Junit的聲明就是如下：
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<scope>test</scope> 這是聲明的範圍，不同的生命周期所要求的範圍是不一樣的，詳情參考《Maven實戰》
</dependency> 首先先來說說Maven下載下傳jar包的過程：
在Maven中會涉及到幾種倉庫：
1 工作空間，即我們的項目工程，這裡面可能會放着pom.xml檔案，這個pom.xml就是maven的配置檔案
2 本地倉庫，本地倉庫用于存放jar包，其實Jar包并不是直接放入工作空間的，它是存放在本地倉庫，然後在執行釋出打包的時候，添加依賴路徑
3 私庫：私庫是使用者自己搭建的maven倉庫，用于緩解頻繁從外網下載下傳jar包資源的壓力。而且使用私庫作為緩存層，也相對安全一些。
4 共享倉庫：書中所說的中央倉庫或者一些常用的鏡像網站都屬于這種，國内比較著名的oschina以及163都是不錯的maven倉庫。
當我們在pom中聲明了依賴關系後，參考上面的圖：
1 Maven在執行相關的任務時，會先去本地倉庫檢視是否有該資源，如果有的話，判斷版本是否正确，如果一切都沒問題則直接使用；否則，執行下一步
2 Maven會去配置的共享倉庫中查找，如果找到就拷貝到本地倉庫中；找不到則會給出相關的提示
3 Maven在本地如果搭建了私庫，則會去私庫中查找，找到就拷貝到本地倉庫；找不到就會去共享倉庫中查找，然後放入私庫和本地庫。有了私庫，區域網路内的開發者可以共享依賴，就不用每個人都去外網下載下傳jar包，浪費帶寬了。
關于本地倉庫和共享倉庫的配置都在settings.xml中，這個檔案位于conf中，如果沒有則拷貝一份即可。
<?xml version="1.0" encoding="UTF-8"?>
<!--
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements. See the NOTICE file
distributed with this work for additional information
regarding copyright ownership. The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied. See the License for the
specific language governing permissions and limitations
under the License.
-->
<!--
| This is the configuration file for Maven. It can be specified at two levels:
|
| 1. User Level. This settings.xml file provides configuration for a single user,
| and is normally provided in ${user.home}/.m2/settings.xml.
|
| NOTE: This location can be overridden with the CLI option:
|
| -s /path/to/user/settings.xml
|
| 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.
|
|-->
<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd">
<!-- localRepository
| The path to the local repository maven will use to store artifacts.
|
| Default: ${user.home}/.m2/repository
<localRepository>/path/to/local/repo</localRepository>
-->
<!-- 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
<interactiveMode>true</interactiveMode>
-->
<!-- 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
<offline>false</offline>
-->
<!-- 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.
|-->
<pluginGroups>
<!-- pluginGroup
| Specifies a further group identifier to use for plugin lookup.
<pluginGroup>com.your.plugins</pluginGroup>
-->
</pluginGroups>
<!-- 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
| 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>
<!-- 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>
-->
<!-- 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
| 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.
|-->
<mirrors>
<!-- mirror
| Specifies a repository mirror site to use instead of a given repository. The repository that
| this mirror serves has an ID that matches the mirrorOf element of this mirror. IDs are used
| for inheritance and direct lookup purposes, and must be unique across the set of mirrors.
|
<mirror>
<id>mirrorId</id>
<mirrorOf>repositoryId</mirrorOf>
<name>Human Readable Name for this Mirror.</name>
<url>http://my.repository.com/repo/path</url>
</mirror>
-->
</mirrors>
<!-- profiles
| This is a list of profiles which can be activated in a variety of ways, and which can modify
| the build process. Profiles provided in the settings.xml are intended to provide local machine-
| specific paths and repository locations which allow the build to work in the local environment.
|
| For example, if you have an integration testing plugin - like cactus - that needs to know where
| your Tomcat instance is installed, you can provide a variable here such that the variable is
| dereferenced during the build process to configure the cactus plugin.
|
| As noted above, profiles can be activated in a variety of ways. One way - the activeProfiles
| section of this document (settings.xml) - will be discussed later. Another way essentially
| relies on the detection of a system property, either matching a particular value for the property,
| or merely testing its existence. Profiles can also be activated by JDK version prefix, where a
| value of '1.4' might activate a profile when the build is executed on a JDK version of '1.4.2_07'.
| Finally, the list of active profiles can be specified directly from the command line.
|
| NOTE: For profiles defined in the settings.xml, you are restricted to specifying only artifact
| repositories, plugin repositories, and free-form properties to be used as configuration
| variables for plugins in the POM.
|
|-->
<profiles>
<!-- profile
| Specifies a set of introductions to the build process, to be activated using one or more of the
| mechanisms described above. For inheritance purposes, and to activate profiles via <activatedProfiles/>
| or the command line, profiles have to have an ID that is unique.
|
| An encouraged best practice for profile identification is to use a consistent naming convention
| for profiles, such as 'env-dev', 'env-test', 'env-production', 'user-jdcasey', 'user-brett', etc.
| This will make it more intuitive to understand what the set of introduced profiles is attempting
| to accomplish, particularly when you only have a list of profile id's for debug.
|
| This profile example uses the JDK version to trigger activation, and provides a JDK-specific repo.
<profile>
<id>jdk-1.4</id>
<activation>
<jdk>1.4</jdk>
</activation>
<repositories>
<repository>
<id>jdk14</id>
<name>Repository for JDK 1.4 builds</name>
<url>http://www.myhost.com/maven/jdk14</url>
<layout>default</layout>
<snapshotPolicy>always</snapshotPolicy>
</repository>
</repositories>
</profile>
-->
<!--
| Here is another profile, activated by the system property 'target-env' with a value of 'dev',
| which provides a specific path to the Tomcat instance. To use this, your plugin configuration
| might hypothetically look like:
|
| ...
| <plugin>
| <groupId>org.myco.myplugins</groupId>
| <artifactId>myplugin</artifactId>
|
| <configuration>
| <tomcatLocation>${tomcatPath}</tomcatLocation>
| </configuration>
| </plugin>
| ...
|
| NOTE: If you just wanted to inject this configuration whenever someone set 'target-env' to
| anything, you could just leave off the <value/> inside the activation-property.
|
<profile>
<id>env-dev</id>
<activation>
<property>
<name>target-env</name>
<value>dev</value>
</property>
</activation>
<properties>
<tomcatPath>/path/to/tomcat/instance</tomcatPath>
</properties>
</profile>
-->
</profiles>
<!-- activeProfiles
| List of profiles that are active for all builds.
|
<activeProfiles>
<activeProfile>alwaysActiveProfile</activeProfile>
<activeProfile>anotherAlwaysActiveProfile</activeProfile>
</activeProfiles>
-->
</settings> View Code
其中本地倉庫的配置為：
<localRepository>F:\apache-maven-3.3.9\repo</localRepository> 預設是在 使用者的本地目錄/.m2/repository中。
共享倉庫的位址配置為:
<mirrors>
<mirror>
<id>CN</id>
<name>OSChina Central</name>
<url>http://maven.oschina.net/content/groups/public/</url>
<mirrorOf>central</mirrorOf>
</mirror>
</mirrors> 3 Maven的生命周期與階段
Maven中有三大生命周期，他們互相獨立，分别是：
1 clean 清理
2 default 建構
3 site 建站
一般來說，clean和default比較常用。
每個生命周期又有不同的階段，階段按順序執行，并且可以指定執行結束的階段。建構的時候，會依次從最上面的階段執行到指定的那個階段。
比如,clean有3個階段：
1 pre-clean 執行清理前要完成的工作
2 clean 清理上一次建構生成的檔案
3 post-clean 執行清理後需要完成的工作 當我們輸入mvn clean的時候，執行的是pre-clean和clean兩個階段。
default的階段比較多：
1 validate
2 initialize
3 generate-sources
4 process-sources
5 generate-resources
6 process-resources
7 compile
8 process-classes
9 generate-test-sources
10 process-test-sources
11 generate-test-resources
12 process-test-resources
13 test-compile
14 process-test-classes
15 tet
16 prepare-package
17 package
18 pre-integration-test
19 integration-test
20 post-integration-test
21 verify
22 install
23 deploy 看名字大概就能了解，當執行mvn install的時候，實際會執行validate-->initialize-->...-->verify-->install等二十幾個階段。
為了操作友善，不同的聲明周期可以在一起執行，比如mvn clean install，會先執行clean的階段，在執行install的階段。
在IDE開發環境中，當我們Run as的時候，就可以執行maven clean進行清理，或者執行maven install進行建構，也可以執行maven build同時執行clean和install兩個任務。
基本上了解上面兩個知識點，就足夠日常工作使用了。當然Maven可不止這麼一點點的東西，比如它還涉及到自定義建構任務、間接依賴的管理、插件的使用、私庫的搭建等等，如果需要的話，讀者可以參考《Maven實戰》，這本書講述的很全面了。
作者：xingoo
出處：http://www.cnblogs.com/xing901022
本文版權歸作者和部落格園共有。歡迎轉載，但必須保留此段聲明，且在文章頁面明顯位置給出原文連接配接！